What is Linux?
Linux is the widely used operating system that is used in most security areas like banking across the globe. Many firms use this operating system to enhance security and increase data confidentiality from hackers. Even though many operating systems were available in the market, the importance of this operating system has not decreased in the market. Do you know why? Read the following article to know the details
Let's start our discussion with,
What is an operating system?
An Operating system is software that manages all the hardware resources, associated with a laptop(or) desktop. This operating system is responsible for managing the communication between the software as well as the hardware. Moreover, no software would work without an operating system.
What is Linux?
Similar to Windows and iOS, Linux is an operating system. It is one of the most powerful platforms available on this planet. As an operating system, the Linux software sits below the other software on the computer. This software receives requests from those programs and relays these requests to the computer hardware. This platform was designed similar to the UNIX and is capable of running on a variety of platforms from phones to supercomputers. Since Linux operating system is open-source, the combination of software may vary among the Linux distributions.
Know more on Linux from real-time professionals at Linux Online Training
What is the benefit of the Open Source Operating system?
a)It has the freedom to run the program for any purpose.
b)It has the freedom to study how the program works and allows the user to make the changes
c)It also allows the user to distribute the modified versions to the others.
What does the Linux Operating system consist of?
The Linux operating system comprises of several pieces. They are:
a)Boot loader: This is a software that manages the boot process of the computer. For most users, it might be a splash screen that pops up and eventually goes away to boot an operating system
b)Kernel: This is the core of the system that manages CPU, memory, and peripheral devices. It is the operating system's lower level.
c)Init System: This is a subsystem that bootstraps the user space and is charged with the controlling daemons. Systemd is one of the most widely used init system. This system is responsible for managing the boot process once the initial booting is handed over from the boot loader.
d)Daemons: These are the background services that startup during the boot (or) when you log in to the system.
e)Graphical Server: This is the subsystem that displays graphics on the monitor. It is commonly called the ‘X’ Server (or) X.
f)Desktop Environment: This is a piece that the users interact with. They are many desktop environments to choose from. Each desktop environment includes built-in applications such as file managers, configuration tools, web browsers, and games.
g)Applications: Desktop environments don’t offer a full array of apps. Just like windows and Mac Os, Linux offers thousands of applications that can be easily installed.
How Linux is different from other operating systems?
In many ways, Linux is similar to the other operating system that you have used before. Like another operating system, Linux has a graphical interface and has rich software like word processors, photo editors, video editors, and so on. In the most number of ways, the software creator has made the Linux version of the same program to use on the other systems. On the other hand,
Firstly, Linux is an open-source operating system. The code used to create Linux is free and is available for the users to view, edit for the users with appropriate skills. Even though the core pieces of the Linux operating systems were the same, many Linux distributions include different software operations. Linux users can choose the core components such as display graphics and other user interface components.
What are the Linux distributions?
Many agencies modified the Linux operating system and make their systems. This operating system is available in the different distribution in the market. It provides different flavors of Linux operating systems to the users. Any user can choose any distribution according to the needs. Some of the popular Linux distributions are Ubuntu, Fedora, Linux Mint, Debian, centosos, and many more.
For beginners, ubuntu and Linux mint were extremely useful. And for a proficient developer, Debian and Fedora will be a good choice.
How to use Linux?
We can use Linux as an interactive user interface as well as from the terminal. Different distributions have different distributions but almost all the commands will have the same behavior for all the distributions. You can run Linux from the terminal by pressing “Ctrl + Alt +T ”. And to explore its functionality press the application button given on the left side of your desktop.
What is the difference between Linux and Unix?
Unix is an operating system developed in 1970 at Bell Labs by Ken Thomson. Linux and Unix were similar in many ways. Linux is created to be indistinguishable from Unix. The major differences between Linux and Unix were as follows:
- Linux is an open-source operating system and is freely available to everyone whereas Unix is also an operating system that can be used only by the copyrighters.
- Linux suits best for the home user, developer as well as a student whereas Unix suits best for work stations, mainframes as well as servers.
- Linux is freely distributed and downloaded whereas Unix Copyright vendors decide the different costs for their respective operating systems.
- Linux supports more file system than Unix
- Linux is just a kernel, whereas Unix is a complete system of packages.
- It has higher security that has 60-100 viruses to date whereas Unix has 85-120 viruses to date.
Likewise, there are many differences between Linux and Unix. By reaching the end of this blog, I hope you people have gained enough information regarding Linux. When you interact with the operating system, you people can acquire practical knowledge on this operating system. And you can also get practical exposure to this platform from real-time working professionals at Linux Online Course. In the upcoming post of this blog, I'll be sharing the details on the installation and various commands of the Linux operating system. Meanwhile, have a look at our Linux Interview Questions
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What is Android ?
Gadgets have become a part of life. Today arrival, as well as utilization of gadgets, is increasing exponentially. And we people cannot imagine our life without gadgets. Today even kindergarten people were using these mobile phones. Moreover, in this COVID-19 situation, these gadgets were the common medium for communication. Even the primary standard kids were using these smart gadgets for communication. Among those many gadgets that were available in the market, the smartphone is the most commonly utilized gadget among people. In the last decade, the smartphone is a big thing that is utilized by business people. But, in this decade, this has become the most common gadget among people. In most of these gadgets, android is the most commonly utilized operating system. Even there are many other operating systems like ios, Linux, android stands on the top of those operating systems. Here the surprising thing this platform has arrived after Linux. But this operating system has replaced the Linux. So have your ever think of “ How this operating system has replaced Linux? ” Also “ what makes android so popular? ”. Read the entire article to know the details. Before going to know the in-depth details, let us have an initial look at its definition What is Android? Android is an open-source Linux operating system for mobile devices such as smartphones and tablet computers. It is developed by Open Handset Alliance This platform offers a unified approach to application development for mobile devices. This approach makes the application more capable of running the software on different android devices. This Android platform has been divided into various versions numbers. These versions were nothing but significant changes from one to the other. The initial beta version for this Software development kit (SDK) by released by google in 2007. And the commercial version Android 1.0 was released in Septemeber 2008. From then it has been continuously releasing the updates. The latest version of Android is Android Q that is the 10th version of this operating system. Today most of the gadgets that were released in 2020 works on Android 9 (or)10. And we were going to expect Android 11 in the next year. Utilization: Even though this application, arose into the market in recent times, today it has become the dominant mobile cross-platform across the globe. According to the stat counter, android holds over 74% of the global mobile OS market share as of July 2020. This operating system was designed with mobile in mind. The place, where the phone applications and applications live. Today everything you see on your device is a part of the operating system. Moreover, whenever your device gets a call, text message (or) an email the OS processes that information and puts it in a readable format. Top Android device manufacturers like Samsung, HTC, Motorola usually have a skin on the top of the OS. A skin is a custom design that adds extra features to your phone with different icons and tweaks designed to provide a unique to your gadget. The popular skins include Samsung One UI and One Plus. A phone without major customization is generally referred to as a stock android and the phone with minor changes was known as near stock. The hardware that supports this software is based on the ARM architecture platform. Today this platform contains millions of apps available that help you to manage your life one (or) the other way. Android programming supports full java programming. Do want to know more on this platform, then visit Android Online Training Since we have gotten the basic idea regarding its utilization, let us have a look at its architecture. Architecture: An android is a software operating system. It contains a stack of software components that is divided into 5 sections and four main layers. They are: Linux kernel: Android uses a powerful Linux kernel and supports a wide range of hardware devices. The kernel is the heart of the operating system that manages the input and output requests from the software. It provides basic system functionalities like process management, memory management, and device management like camera, keypad as well as a display to handle all these things. Linux is good at networking and does not require and does require to interface with the peripheral hardware. The kernel itself does not interact directly with the user but interacts with the shell as well as other hardware devices on the system. Libraries: These were on the top of the Linux kernel. There is a set of libraries including open web browsers such as WebKit, library libc. These libraries are used to play the audio as well as the video files. The SQL lite is a database that is useful for storage as well as sharing the application data. These SSL libraries are responsible for internet security etc Runtime: The runtime provides a key virtual environment known as Dalvik Virtual Machine. It is a kind of java virtual machine that is specifically designed and optimized for android. The Dalvik VM is a process Virtual machine in Android systems. It is a software that runs the app on android devices. The Dalvik VM makes use of many Linux core features like memory management, multithreading that is in java language. This Dalvik VM enables every application to run its process. This Dalvik VM executes the files in .dex format. Application Framework: The application framework layer is capable of providing the higher-level services to applications such as windows manager, view system, package manager, resource manager, etc. It allows the application developers to make use of there services in their application Features: This application framework has a rich set of features. Some of them were : a)It is an open-source b)Anyone can customize this application platform c)Availability of a huge number of applications. Hence the customer can choose the best product as per the need d)Capable of providing interesting features like Whether details, Opening screen, RSS feeds, etc e) Has an ability to provide support for the messaging services (SMS and MMS), Web browser, Storage(SQL Lite), Connectivity(GSM, CDMA, Bluetooth, WIFI, media, handset layout. Hence likewise there are many interesting features of this operating application. You people can get hands-on experience on application development on this platform through Android Online Course. I hope you people have got enough idea regarding Android. In the upcoming post of this blog, I'll be sharing the details of the runtime environment and the basic program on the android platform. Meanwhile, have a glance at our Android Interview Questions and get ready to crack the interview.
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What is Linux?
Linux is the widely used operating system that is used in most security areas like banking across the globe. Many firms use this operating system to enhance security and increase data confidentiality from hackers. Even though many operating systems were available in the market, the importance of this operating system has not decreased in the market. Do you know why? Read the following article to know the details Let's start our discussion with, What is an operating system? An Operating system is software that manages all the hardware resources, associated with a laptop(or) desktop. This operating system is responsible for managing the communication between the software as well as the hardware. Moreover, no software would work without an operating system. What is Linux? Similar to Windows and iOS, Linux is an operating system. It is one of the most powerful platforms available on this planet. As an operating system, the Linux software sits below the other software on the computer. This software receives requests from those programs and relays these requests to the computer hardware. This platform was designed similar to the UNIX and is capable of running on a variety of platforms from phones to supercomputers. Since Linux operating system is open-source, the combination of software may vary among the Linux distributions. Know more on Linux from real-time professionals at Linux Online Training What is the benefit of the Open Source Operating system? a)It has the freedom to run the program for any purpose. b)It has the freedom to study how the program works and allows the user to make the changes c)It also allows the user to distribute the modified versions to the others. What does the Linux Operating system consist of? The Linux operating system comprises of several pieces. They are: a)Boot loader: This is a software that manages the boot process of the computer. For most users, it might be a splash screen that pops up and eventually goes away to boot an operating system b)Kernel: This is the core of the system that manages CPU, memory, and peripheral devices. It is the operating system's lower level. c)Init System: This is a subsystem that bootstraps the user space and is charged with the controlling daemons. Systemd is one of the most widely used init system. This system is responsible for managing the boot process once the initial booting is handed over from the boot loader. d)Daemons: These are the background services that startup during the boot (or) when you log in to the system. e)Graphical Server: This is the subsystem that displays graphics on the monitor. It is commonly called the ‘X’ Server (or) X. f)Desktop Environment: This is a piece that the users interact with. They are many desktop environments to choose from. Each desktop environment includes built-in applications such as file managers, configuration tools, web browsers, and games. g)Applications: Desktop environments don’t offer a full array of apps. Just like windows and Mac Os, Linux offers thousands of applications that can be easily installed. How Linux is different from other operating systems? In many ways, Linux is similar to the other operating system that you have used before. Like another operating system, Linux has a graphical interface and has rich software like word processors, photo editors, video editors, and so on. In the most number of ways, the software creator has made the Linux version of the same program to use on the other systems. On the other hand, Firstly, Linux is an open-source operating system. The code used to create Linux is free and is available for the users to view, edit for the users with appropriate skills. Even though the core pieces of the Linux operating systems were the same, many Linux distributions include different software operations. Linux users can choose the core components such as display graphics and other user interface components. What are the Linux distributions? Many agencies modified the Linux operating system and make their systems. This operating system is available in the different distribution in the market. It provides different flavors of Linux operating systems to the users. Any user can choose any distribution according to the needs. Some of the popular Linux distributions are Ubuntu, Fedora, Linux Mint, Debian, centosos, and many more. For beginners, ubuntu and Linux mint were extremely useful. And for a proficient developer, Debian and Fedora will be a good choice. How to use Linux? We can use Linux as an interactive user interface as well as from the terminal. Different distributions have different distributions but almost all the commands will have the same behavior for all the distributions. You can run Linux from the terminal by pressing “Ctrl + Alt +T ”. And to explore its functionality press the application button given on the left side of your desktop. What is the difference between Linux and Unix? Unix is an operating system developed in 1970 at Bell Labs by Ken Thomson. Linux and Unix were similar in many ways. Linux is created to be indistinguishable from Unix. The major differences between Linux and Unix were as follows: Linux is an open-source operating system and is freely available to everyone whereas Unix is also an operating system that can be used only by the copyrighters. Linux suits best for the home user, developer as well as a student whereas Unix suits best for work stations, mainframes as well as servers. Linux is freely distributed and downloaded whereas Unix Copyright vendors decide the different costs for their respective operating systems. Linux supports more file system than Unix Linux is just a kernel, whereas Unix is a complete system of packages. It has higher security that has 60-100 viruses to date whereas Unix has 85-120 viruses to date. Likewise, there are many differences between Linux and Unix. By reaching the end of this blog, I hope you people have gained enough information regarding Linux. When you interact with the operating system, you people can acquire practical knowledge on this operating system. And you can also get practical exposure to this platform from real-time working professionals at Linux Online Course. In the upcoming post of this blog, I'll be sharing the details on the installation and various commands of the Linux operating system. Meanwhile, have a look at our Linux Interview Questions
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Advanced Linux Interview Questions
Q.What Is The Difference Between Ctrl-c And Ctrl-z? Ans: When you have a process in progress which handle your prompt, there are some signals (orders) that we can send to theses process to indicate what we need: Control+C sends SIGINT which will interrupt the application. Usually causing it to abort, but a process is able to intercept this signal and do whatever it likes: for instance, from your Bash prompt, try hitting Ctrl-C. In Bash, it just cancels whatever you've typed and gives you a blank prompt (as opposed to quitting Bash) Control+Z sends SIGTSTP to a foreground application, effectively putting it in the background on suspended mode. This is very useful when you want the application to continue its process while you are doing another job in the current shell. When you finish the job, you can go back into the application by running fg (or %x where x is the job number as shown in jobs). Q.I Want To Troubleshoot My Network But I Don’t Know How Does The Traceroute Command Work Exactly? Ans: Traceroute is a program that shows you the route taken by packets through a network. It traces the route of packets from source to destination. It is commonly used when your network doesn’t work as well and you want to examine where can be the problem. Traceroute sends a UDP packet to the destination taking advantage of ICMP’s messages. ICMP has two types of messages: error-reporting messages and query messages. Query messages are generally used to diagnose network problems (the ping tool uses ICMP’s query messages). The error-reporting messages as the name suggest report errors if any in the IP packet; it uses Destination unreachable and Time exceeded errors message. It works by theses steps: Traceroute creates a UDP packet from the source to destination with a TTL(Time-to-live) = 1 The UDP packet reaches the first router where the router decrements the value of TTL by 1, thus making our UDP packet’s TTL = 0 and hence the packet gets dropped. Noticing that the packet got dropped, it sends an ICMP message (Time exceeded) back to the source. Traceroute makes a note of the router’s address and the time taken for the round-trip. It sends two more packets in the same way to get an average value of the round-trip time. Usually, the first round-trip takes longer than the other two due to the delay in ARP finding the physical address, the address stays in the ARP cache during the second and the third time and hence the process speeds up. The steps that have occurred up til now, occur again and again until the destination has been reached. The only change that happens is that the TTL is incremented by 1 when the UDP packet is to be sent to next router/host. Once the destination is reached, Time exceeded ICMP message is NOT sent back this time because the destination has already been reached. But, the UDP packet used by Traceroute specifies the destination port number to be one that is not usually used for UDP. Hence, when the destination computer verifies the headers of the UDP packet, the packet gets dropped due to the improper port being used and an ICMP message (this time – Destination Unreachable) is sent back to the source. When Traceroute encounters this message, it understands that the destination has been reached. Even the destination is reached 3 times to get the average of the round-trip time. Q.Nscd Sometimes Die Itself And Dns Resolving Doesn't Happen Properly. How Can We Avoid Nscd For Dns And There Is A Disadvantage To Bypass It? Ans: nscd is a daemon that provides a cache for the most common name service requests. When resolving a user, group, host, service..., the process will first try to connect to the nscd socket (something like /var/run/nscd/socket). If nscd has died, the connect will fail, and so nscd won't be used and that should not be a problem. If it's in a hung state, then the connect may hang or succeed. If it succeeds the client will send its request (give IP address for www.google.com, passwd entries...). Now, you can configure nscd to disable caching for any type of database (for instance by having enable-cache hosts no in /etc/nscd.conf for the hosts database). However, if nscd is in a hung state, it may not be able to even give that simple won't do answer, so that won't necessarily help. nscd is a caching daemon, it's meant to improve performance. Disabling it would potentially make those lookups slower. However, that's only true for some kind of databases. For instance, if user/service/group databases are only in small files (/etc/passwd, /etc/group, /etc/services), then using nscd for those will probably bring little benefit if any. nscd will be useful for the hosts database. Q. How Can I Redirect Both Stderr And Stdin At Once? Ans: command > file.log 2>&1 : Redirect stderr to "where stdout is currently going". In this case, that is a file opened in append mode. In other words, the &1 reuses the file descriptor which stdout currently uses. command 2>&1 | tee -a file.txt Q. What Is The Difference Between /dev/random And /dev/urandom To Generate Random Data? Ans: The Random Number Generator gathers environmental noise from device drivers and other sources into entropy pool. It also keeps an estimate of Number of bits of noise in entropy pool. It is from this entropy pool, random numbers are generated. /dev/random will only return Random bytes from entropy pool. If entropy pool is empty, reads to /dev/random will be blocked until additional environmental noise is gathered. This is suited to high-quality randomnesses, such as one-time pad or key generation. /dev/urandom will return as many random bytes as requested. But if the entropy pool is empty, it will generate data using SHA, MD5 or any other algorithm. It never blocks the operation. Due to this, the values are vulnerable to theoretical cryptographic attack, though no known methods exist. For cryptographic purposes, you should really use /dev/random because of nature of data it returns. Possible waiting should be considered as an acceptable tradeoff for the sake of security, IMO. When you need random data fast, you should use /dev/urandom of course. Both /dev/urandom and /dev/random are using the exact same CSPRNG (a cryptographically secure pseudorandom number generator). They only differ in very few ways that have nothing to do with “true” randomness and /dev/urandom is the preferred source of cryptographic randomness on UNIX-like systems. Q. What Is The Difference Between Tar And Zip ? Ans: Sometimes sysadmins Linux need to save data safety and to this, it is recommended to compress the data. We have some methods or commands for compression on Linux. So frequently asked questions could be why should I use this command instead of another one example, why should I use tar instead of zip. To answer this, you should know the difference between the two. tar is only an archiver whereas zip is an archiver and compressor. Tar uses gzip and bzip2 to achieve compression. With using tar command, we preserve metadata information of file and directories like seiuid, setgid and sticky bit information which are very important while zip doesn't preserve theses information. It is very important for criticals information. Other advantages of using tar is the fact that it assembles all the files into a single file to compress directly while zip compress file by file. Q. How To Check Open Ports On A Remote Server Without Netcat Or Nmap Linux Command? Ans: In the work of sysadmin, we can sometimes want to check open ports on our remote server. But if we are on a machine where can not install nmap or we don't have the possibility to install a tool which can help us to check open ports, what could we do? We can check it with bash using /dev/tcp or /dev/udp to open a TCP or UDP connection to the associated socket. The command behavior is: $ echo > /dev/tcp/$host/$port we can associate a message to display if the port is opened $ echo > /etc/tcp/8.8.8.8/53 && echo "OPEN PORT" OPEN PORT $ echo > /dev/tcp/8.8.8.8/80 && echo "GOOD" || echo "NOT OPEN" -bash: connect: Connection timed out -bash: /dev/tcp/8.8.8.8/80: Connection timed out NOT OPEN Q. Systemd Over Init System, What Do You Think? Ans: Systemd is well designed. It was conceived from the top, not just to fix bugs, but to be a correct implementation of the base system services. A systemd, may refer to all the packages, utilities and libraries around daemon. It was designed to overcome the shortcomings of init. It itself is a background process which is designed to start processes in parallel, thus reducing the boot time and computational overhead. It has a lot other features as compared to init while Sysvinit was never designed to cope with the dynamic/event-based architecture of the current Linux kernel. The only reason why we still use it today is the cost of a migration. Systemd ships a growing number of useful, unified command-line interfaces for system settings and control (timedatectl, bootctl, hostnamectl, loginctl, machinectl, kernel-install, localectl). In Debian, they use the existing configuration files without breaking compatibility. Systemd makes the boot process much simpler, entirely removing the need to specify dependencies in many cases thanks to D-Bus activation, socket activation, file/inotify activation and udev integration. Systemd supports SELinux integration while SysV doesn't Systemd can handle the boot process from head to toe, without needing to use any of the existing shell scripts. Systemd extends the logging features of the system in many ways with journald, and can remain integrated with the existing rsyslog daemon. Logs are in a structured format, attributed to filename, line of code, PID and service. They include the early boot (starting from initramfs). They can be quickly filtered and programmatically accessed through an efficient interface. Systemd unit files, unlike SysV scripts, can usually be shipped by upstream, or at least shared with other distributions (already more than 1000 existing unit files in Fedora) without any changes, the Debian specifics being handled by systemd itself. Systemd is incredibly fast (1 second to boot). It was not designed with speed in mind, but doing things correctly avoids all the delays currently incurred by the boot process. The transition plan is easy, since existing init scripts are treated as first-class services: scripts can depend (using LSB headers) on units, units can depend on scripts. More than 99% of init scripts can be used without a modification. It is not just init. It unifies, in fewer lines of code, everything that is related to starting services and managing session groups: user login, cron jobs, network services (inetd), virtual TTY management… Having a single system to handle all of that allows us to remove a lot of cruft, and to use less memory on the system. Q.What Basics Measures Could You Take To Secure An Ssh Connection? Ans: For Linux sysadmins, it is frequent to access servers by ssh. But are we sure the communication established is really good secured? There some additionals very simple steps that can be taken to initially harden the SSH service, such as: Disabling root login, and even password-based logins will further reinforce the security of the server. Disabling password-based logins and allow key based logins which are secured but can be taken further by restricting their use from only certain IP addresses. Changing the standard port to something other significantly decreases random brute force attempts from the internet Forcing the service to use only version 2 of the protocol will introduce both security and feature enhancement. The whitelist approach can be taken, where only the users that belong to a certain list can log in via SSH to the server. Q.What Is Lvm And Does It Required On Linux Servers? Ans : LVM is a logical volume manager. It requires to resize filesystem size. This size can be extended and reduced using lvextend and lvreduce commands respectively. You can think of LVM as dynamic partitions, meaning that you can create/resize/delete LVM partitions from the command line while your Linux system is running: no need to reboot the system to make the kernel aware of the newly-created or resized partitions. LVM also provides: You can extend over more than one disk if you have more than one hard-disk. They are not limited by the size of one single disk, rather by the total aggregate size. You can create a (read-only) snapshot of any LV (Logical Volume). You can revert the original LV to the snapshot at a later time, or delete the snapshot if you no longer need it. This is handy for server backups for instance (you cannot stop all your applications from writing, so you create a snapshot and backup the snapshot LV), but can also be used to provide a "safety net" before a critical system upgrade (clone the root partition, upgrade, revert if something went wrong). you can also set up writeable snapshots too. It allows you to freeze an existing Logical Volume in time, at any moment, even while the system is running. You can continue to use the original volume normally, but the snapshot volume appears to be an image of the original, frozen in time at the moment you created it. You can use this to get a consistent filesystem image to back up, without shutting down the system. You can also use it to save the state of the system, so that you can later return to that state if you mess things up. You can even mount the snapshot volume and make changes to it, without affecting the original. Contact for more on Linux Online Training
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Android Interview Questions
Q.What Is Android? Ans: Android is a stack of software for mobile devices which has Operating System, middleware and some key applications. The application executes within its own process and its own instance of Dalvik Virtual Machine. Many Virtual Machines run efficiently by a DVM device. DVM executes Java languages byte code which later transforms into .dex format files. Q.Explain About The Exceptions Of Android? Ans: The following are the exceptions that are supported by Android * InflateException : When an error conditions are occurred, this exception is thrown * Surface.OutOfResourceException: When a surface is not created or resized, this exception is thrown * SurfaceHolder.BadSurfaceTypeException: This exception is thrown from the lockCanvas() method, when invoked on a Surface whose is SURFACE_TYPE_PUSH_BUFFERS * WindowManager.BadTokenException: This exception is thrown at the time of trying to add view an invalid WindowManager.LayoutParamstoken. Q.Why To Use Android? Ans: Android is useful because: *It is simple and powerful SDK *Licensing, Distribution or Development fee is not required *Easy to Import third party Java library *Supporting platforms are ? Linux, Mac Os, Windows Q.Describe Android Application Architecture? Ans: Android Application Architecture has the following components: * Services - like Network Operation * Intent - To perform inter-communication between activities or services * Resource Externalization - such as strings and graphics * Notification signaling users - light, sound, icon, notification, dialog etc. * Content Providers - They share data between applications Q.What Are The Features Of Android? Ans: *Components can be reused and replaced by the application framework. *Optimized DVM for mobile devices *SQLite enables to store the data in a structured manner. *Supports GSM telephone and Bluetooth, WiFi, 3G and EDGE technologies *The development is a combination of a device emulator, debugging tools, memory profiling and plug-in for Eclipse IDE. Q.Are The Android Releases Available In A Rom? Ans: No, Android is not yet available in a ROM format. Currently Android is installed by using a clean SD Card, and booted from there. It is booted by running a special application called 'Haret.exe' residing on your SD Card which will terminate the Windows kernel and boot into Linux/Android. It can't easily be run from ROM because a) it's too experimental to risk putting in ROM and then killing a device and b) WinMo does some hardware initialisation that isn't documented, but is needed before Android can run. Q.Can You Play Android 2.1 Games On Android 2.2? Ans: no.as i have a 2.2 android phone, its very hard to find games for it. The 2.2 android will not be able to support that type of game. Q.What Is Android Runtime? Ans: Android includes a set of core libraries that provides most of the functionality available in the corelibraries of the Java programming language. Every Android application runs in its own process, with its own instance of the Dalvik virtual machine. Dalvik has been written so that a device can run multiple VMs efficiently. The Dalvik VM executes files in the Dalvik Executable (.dex) format which is optimized for minimal memory footprint. The VM is register-based, and runs classes compiled by a Java language compiler that have been transformed into the .dex format by the included ?dx? tool. Q.Creating An Android Application Using The Eclipse Plugin? Ans: Using the Android Eclipse plugin is the fastest and easiest way to start creating a new Androidapplication. The plugin automatically generates the correct project structure for your application, and keeps the resources compiled for you automatically. It is still a good idea to know what is going on though. Take a look at Overview of an AndroidApplication to understand the basics of how an Android application works. It is also recommended that you take a look at the ApiDemos application and the other sample applications in the samples/ folder in the SDK. Finally, a great way to started with Android development in Eclipse is to follow both the Hello Android and Notepad code tutorials. In particular, the start of the Hello Android tutorial is an excellent introduction to creating a new Android application in Eclipse. Q.Can I Write Code For Android Using C/c++? Ans: Android applications are written using the Java programming language.Android includes a set of core libraries that provides most of the functionality available in the core libraries of the Java programming language.Every Android application runs in its own process, with its own instance of the Dalvik virtual machine. Dalvik has been written so that a device can run multiple VMs efficiently. The Dalvik VM executes files in the Dalvik Executable (.dex) format which is optimized for minimal memory footprint. The VM is register-based, and runs classes compiled by a Java language compiler that have been transformed into the .dex format by the included ?dx? tool.Android only supports applications written using the Java programming language at this time. Q.What Is The Ttl (time To Live)? Why Is It Required? Ans: TTL is a value in data packet of Internet Protocol. It communicates to the network router whether or not the packet should be in the network for too long or discarded. Usually, data packets might not be transmitted to their intended destination within a stipulated period of time. The TTL value is set by a system default value which is an 8-bit binary digit field in the header of the packet. The purpose of TTL is, it would specify certain time limit in seconds, for transmitting the packet header. When the time is exhausted, the packet would be discarded. Each router receives the subtracts count, when the packet is discarded, and when it becomes zero, the router detects the discardedpackets and sends a message, Internet Control Message Protocol message back to the originating host. TTL(time to live) apart from determining the life time of a packet in a network also helps in avoiding the wastage of bandwith Q.How Is Nine-patch Image Different From A Regular Bitmap? Ans: It is a resizable bitmap resource that can be used for backgrounds or other images on the device. The NinePatch class permits drawing a bitmap in nine sections. The four corners are unscaled; the four edges are scaled in one axis, and the middle is scaled in both axes. Q.Explain Ip Datagram, Fragmentation And Mtu ? Ans: IP datagram can be used to describe a portion of IP data. Each IP datagram has set of fields arranged in an order. The order is specific which helps to decode and read the stream easily. IP datagram has fields like Version, header length, Type of service, Total length, checksum, flag, protocol, Time to live, Identification, source and destination ip address, padding, options and payload. MTU:- Maximum Transmission Unit is the size of the largest packet that a communication protocol can pass. The size can be fixed by some standard or decided at the time ofconnection Fragmentation is a process of breaking the IP packets into smaller pieces. Fragmentation is needed when the datagram is larger than the MTU. Each fragment becomes a datagram in itself and transmitted independently from source. When received by destination they are reassembled. Q.What Is Sticky Intent? Ans: Is there anyway to determine if an Intent passed into a BroadcastReceiver's onReceive is the result of a sticky Boradcast Intent, or if it was just sent. Q.User-generated Content: Report Abuse Which Is The Better Phone - The Iphone Or The Droid? Ans: The iphone 4 is better than any other phone. for one it is made out of the same material they use in helicopter and train windows.(atleas from what i haerd)another thing is that the iphone has a better app market. with over 300,000 apps it is far better than the droids 70,000. Also it comes with more accesories and has an antenna to provide better signal while the droid doesn't. People say it has a bad connection but i think not since i have already used it. And last but not leats better resolution. it may have a smaller screen but still its graphics are better.so it all depends on you each one has its ups and its downs but i would go with iphone 4 over any phone especially the "all new droid x" Q.How Long Does It Take To Build An App? Ans: Depending on the complexity and how quickly you respond to us you could have an app built in about a month. Q.How Much Does Mobile Application Development Cost? That Is A Bit Like Asking: How Much Does A Truck Cost? Ans: The answer is that it depends on the truck. Your needs are unique and your app needs to meet only those needs. A small Toyota will cost a lot less than a huge semi tractor trailer. A tractor trailer is great if you want to haul goods across the country but dont try to take it on a Saturday night date. We help you to avoid creating too much - or too little app. This keeps costs low. Having us create a custom smartphone app is surprisingly affordable. Many businesses find their app costs less than even a small radio or newspaper campaign. Unlike a radio campaign, the app?s usefulness does not end with the last commercial. Once it is created an app can add to your bottom line for a very long time. Our goal is to connect your audience with your cash register no matter where they are. With a smartphone app you give your customers access to you at the exact moment their buying decision is the strongest. Q. Describe The Apk Format. Ans: The APK file is compressed the AndroidManifest.xml file, application code (.dex files), resource files, and other files. A project is compiled into a single .apk file. Q.Is Sim Pin Code Working? Ans: It's supposed to be working, yes, but if you have ANY troubles please DISABLE SIM PIN in WinMo (SIM PIN works on the SIM, but you need WinMo UI to disable it) Q.What Is The Future Scope Of Mobile Application Developers? Ans: Future of the mobile application development is bright Q.What Is The Mobile Application Development All About? Ans: In the last two years, a lot of innovation has come in the mobile computing world. Apple has launched very innovative mobile phone, iphone and ipad along with app store. Google launched Android in Nov 2007. Blackberry released SDK and app world. Microsoft has come up with phone 7 framework. Almost every type of mobile can be programmed using J2ME. Making applications for all these devices is Mobile application development. Q.What Is The Demand Of Mobile Application Developers? Ans: Desktop based IT application is present but the mobile is future. All the applications that were madeto work only on desk top are being ported to mobile. In the coming 10 years, desktops will be replaced completely with mobile, and then all the applications will be designed mainly for mobile. The demand for mobile based trained engineers are increasing every year. Now after the launch of ipad by Apple, it will be even more. Therefore; the gextgen technology will be nothing else than mobile. The demand is expected to grow 70 folds in the coming 4 years. Q.What Is The Risk In Blocking The Main Thread When Performing A Lengthyoperation Such As Web Access Or Heavy Computation? Ans: Application_Not_Responding exception will be thrown which will crash and restart the application. Q.What Is A Dalvik ? Ans: The name of Androids virtual machine. The Dalvik VM is an interpreter-only virtual machine that executes files in the Dalvik Executable (.dex) format, a format that is optimized for efficient storage and memory-mappable execution. The virtual machine is register-based, and it can run classes compiled by a Java language compiler that have been transformed into its native format using the included ?dx? tool. The VM runs on top of Posix-compliant operating systems, which it relies on for underlying functionality (such as threading and low level memory management). The Dalvik core class library is intended to provide a familiar development base for those used to programming with Java Standard Edition, but it is geared specifically to the needs of a small mobile device. Q.What Features Are In A Release? Ans: Generally, it's very difficult to detail them, unless there is a significant new feature (in which case, that will be very well advertised!). Usually it's minor speed improvements, bug fixes etc... and sometimes, new bugs are introduced (so bear that in mind) Q.When Will It Be Available In A Rom? Ans: No time soon. Folks are working on it, but you'll need a lot of patience before it (if ever) arrives. Q. I Keep Hearing 'popping/clicking' Sounds From The Speaker? Ans: This is a known annoyance on some devices, believed to be related to power management switching the speaker on and off (not confirmed), it actually seems worse in silent mode (ironically). If you experience this, you're not alone... most users do. When a fix is ready, it will be announced here. Q.How Much Revenue Share Does The Developer Get? Ans: The developer gets 70% revenue generated from each Android application purchase while the rest is used for settlement charges. Google doesn't take a dime out of this. Q.Explain Seapine Software? Ans: Seapine's software development and testing tools streamline your development process, saving you significant time and money. Enjoy feature-rich tools that are flexible enough to work in any software development environment. With Seapine integrated tools, every step in the developmentprocess feeds critical information into the next step, letting you focus on developing high quality software in less time. Q.Why Is List View Not Recommended To Have Active Components? Ans: Clicking on the active text box will pop up the software keyboard but this will resize the list, removing focus from the clicked element. Q.Why Is Open Platform Good For The Mobile Operators? Ans: An open platform would foster faster innovation, multiple software versions, better customisation options, lower costs, which would bring down the overall service and handset costs while boostingsales. Q.Describe A Real Time Scenario Where Android Can Be Used? Ans: Imagine a situation that you are in a country where no one understands the language you speak and you can not read or write. However, you have mobile phone with you. With a mobile phone with android, the Google translator translates the data of one language into another language by using XMPP to transmit data. You can type the message in English and select the language which is understood by the citizens of the country in order to reach the message to the citizens. Q.Why Is Open Platform Good For Developers? Ans: Developers will be able innovate rapidly because they will have comprehensive API access tohandset capabilities that are web-ready. They will experience increased productivity because they will have comprehensive and easy-to-use developer tools. And because open source offers a deeper understanding of the underlying mobile platform, they can better optimise their applications. Finally, the distribution and commercialisation of mobile apps will be less expensive and easier. Q.How Will You Record A Phone Call In Android? How To Get A Handle On Audiostream For A Call In Android? Ans: Permissions.PROCESS_OUTGOING_CALLS: Allows an application to monitor, modify, or abort outgoingcalls. Q.What Is An Ddms? Ans: Dalvik Debug Monitor Service, a GUI debugging application shipped with the SDK. It provides screen capture, log dump, and process examination capabilities. Q.What Are The Advantages Of Android? Ans: The following are the advantages of Android: * The customer will be benefited from wide range of mobile applications to choose, since themonopoly of wireless carriers like AT&T and Orange will be broken by Google Android. * Features like weather details, live RSS feeds, opening screen, icon on the opening screen can be customized * Innovative products like the location-aware services, location of a nearby convenience store etc., are some of the additive facilities in Android. Q.Does Android Support The Bluetooth Serial Port Profile? Ans: Yes. Q.What Is The Android G1 Phone? Ans: The Android T-Mobile G1 phone is the world's first Android-powered mobile phone developed by HTC and T-Mobile. Q.Which Is The Virtual Machine Used To Run The Android Apps? Ans: The VM used is called Dalvik, so named after the ancestral roots of its creator, as the story goes. Q.Are The Android Apps First Scrutinised By Google? Ans: No the Android applications can be directly posted on the Android Market once you are registered as a developer after paying the $25 application fee. Q.What Is An Intent Receiver? Ans: An application class that listens for messages broadcast by calling Context.broadcastIntent Q.What's The Difference Between File, Class And Activity In Android? Ans: File - It is a block of arbitrary information, or resource for storing information. It can be of any type. Class - Its a compiled form of .Java file . Android finally used this .class files to produce an executable apk. Activity - An activity is the equivalent of a Frame/Window in GUI toolkits. It is not a file or a file type it is just a class that can be extended in Android for loading UI elements on vie Q.How To Select More Than One Option From List In Android Xml File? Give An Example. Ans: Specify android id, layout height and width as depicted in the following example. Q.What Languages Does Android Support For Application Development? Ans: Android applications are written using the Java programming language. Q.What Are The Dialog Boxes That Are Supported In Android? Explain. Ans: Android supports 4 dialog boxes: AlertDialog : An alert dialog box supports 0 to 3 buttons and a list of selectable elements, including check boxes and radio buttons. Among the other dialog boxes, the most suggested dialog box is the alert dialog box. ProgressDialog: This dialog box displays a progress wheel or a progress bar. It is an extension of AlertDialog and supports adding buttons. DatePickerDialog: This dialog box is used for selecting a date by the user. TimePickerDialog: This dialog box is used for selecting time by the user. Q.What Virtual Machine Android Runs On? Ans: Dalvik virtual machine Q.What Are The Differences Between A Domain And A Workgroup? Ans: In a domain, one or more computer can be a server to manage the network. On the other hand in aworkgroup all computers are peers having no control on each other. In a domain, user doesn?t needan account to logon on a specific computer if an account is available on the domain. In a work group user needs to have an account for every computer. In a domain, Computers can be on different local networks. In a work group all computers needs to be a part of the same local network. Q.How To Remove Desktop Icons And Widgets? Ans: Press and Hold the icon or widget. The phone will vibrate and on the bottom of the phone you will see anoption to remove. While still holding the icon or widget drag it to the remove button. Once remove turns red drop the item and it is gone. Q.What Is .apk Extension? Ans: The extension for an Android package file, which typically contains all of the files related to a single Android application. The file itself is a compressed collection of an AndroidManifest.xml file,application code (.dex files), resource files, and other files. A project is compiled into a single .apk file. Q.What Is A Layout Resource? Ans: An XML file that describes the layout of an Activity screen. Q.What Is A Manifest ? Ans: An XML file associated with each Application that describes the various activies, intent filters, services, and other items that it exposes. Q.What Is A Theme ? Ans: A set of properties (text size, background color, and so on) bundled together to define various default display settings. Android provides a few standard themes, listed in R.style (starting with ?Theme_?). Q.What Is An Uris? Ans: Android uses URI strings both for requesting data (e.g., a list of contacts) and for requesting actions (e.g., opening a Web page in a browser). Both are valid URI strings, but have different values. All requests for data must start with the string ?content://?. Action strings are valid URIs that can be handled appropriately by applications on the device; for example, a URI starting with ?http://? will be handled by the browser. Q.Can An Application Be Started On Powerup? Ans: Yes. Q.What Is An Action? Ans: A description of something that an Intent sender desires. Q.What Is Activity? Ans: A single screen in an application, with supporting Java code. Q.What Is Intent? Ans: A class (Intent) describes what a caller desires to do. The caller sends this intent to Android's intent resolver, which finds the most suitable activity for the intent. Q.What Is A Resource? Ans: A user-supplied XML, bitmap, or other file, injected into the application build process, which can later be loaded from code. Q.What Is A Sticky Intent? Ans: sendStickyBroadcast() performs a sendBroadcast (Intent) that is "sticky," i.e. the Intent you are sending stays around after the broadcast is complete, so that others can quickly retrieve that data through the return value of registerReceiver (BroadcastReceiver, IntentFilter). In all other ways, this behaves the same as sendBroadcast (Intent). One example of a sticky broadcast sent via the operating system is ACTION_BATTERY_CHANGED. When you call registerReceiver () for that action -- even with a null BroadcastReceiver -- you get the Intent that was last broadcast for that action. Hence, you can use this to find the state of the battery without necessarily registering for all future state changes in the battery. Q.What Is The Open Handset Alliance? Ans: The OHA is a consortium of 30 technology and mobile companies that have joined hands to accelerate innovation in mobile technology and at the same time offer the end users a better, costeffective and richer mobile experience. Q.What Innovations The Oha Members Strive To Achieve? Ans: The OHA members have endeavored to develop Android, the open source mobile platform consisting of an OS, web browser and key applications. Different companies have different contributions to make and roles to play. For instance, the software companies like Google are developing the requisite software, the hardware companies the chipsets and the mobile companies are ensuring compatible handsets for Android. Q.Why An Open Source Platform Would Be Beneficial To Consumers? Ans: Open source platform will ensure cheaper mobile handsets and services coupled with richer user experience in the form of a friendlier interface, cool applications and an enhanced browsing experience. Q.How Will Apps Change With Android 2.2? Ans: The answer is that with Froyo, Google's giving us a bunch of new ways to take advantage of apps from the Android Market and beyond. The highlights:SD card installations: you'll finally be able to install apps on your SD card, smashing the space limitations of Android versions past. You'll be able to select where you want each app to be installed - SD card or internal storage - and even toggle it back and forth with a couple of clicks later. android online training
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Linux Interview Questions
Q.How are devices represented in UNIX? Ans: All devices are represented by files called special files that are located in/dev directory. Thus, device files and other files are named and accessed in the same way. A 'regular file' is just an ordinary data file in the disk. A 'block special file' represents a device with characteristics similar to a disk (data transfer in terms of blocks). A 'character special file' represents a device with characteristics similar to a keyboard (data transfer is by stream of bits in sequential order). Q.What is 'inode'? All UNIX files have its description stored in a structure called 'inode'. The inode contains info about the file-size, its location, time of last access, time of last modification, permission and so on. Directories are also represented as files and have an associated inode. In addition to descriptions about the file, the inode contains pointers to the data blocks of the file. If the file is large, inode has indirect pointer to a block of pointers to additional data blocks (this further aggregates for larger files). A block is typically 8k. Inode consists of the following fields: File owner identifier File type File access permissions File access times Number of links File size Location of the file data Q.Brief about the directory representation in UNIX Ans: A Unix directory is a file containing a correspondence between filenames and inodes. A directory is a special file that the kernel maintains. Only kernel modifies directories, but processes can read directories. The contents of a directory are a list of filename and inode number pairs. When new directories are created, kernel makes two entries named '.' (refers to the directory itself) and '..' (refers to parent directory). System call for creating directory is mkdir (pathname, mode). Q.What are the Unix system calls for I/O? Ans: open(pathname,flag,mode) - open file creat(pathname,mode) - create file close(filedes) - close an open file read(filedes,buffer,bytes) - read data from an open file write(filedes,buffer,bytes) - write data to an open file lseek(filedes,offset,from) - position an open file dup(filedes) - duplicate an existing file descriptor dup2(oldfd,newfd) - duplicate to a desired file descriptor fcntl(filedes,cmd,arg) - change properties of an open file ioctl(filedes,request,arg) - change the behaviour of an open file The difference between fcntl anf ioctl is that the former is intended for any open file, while the latter is for device-specific operations. Q.How do you change File Access Permissions? Ans: Every file has following attributes: owner's user ID ( 16 bit integer ) owner's group ID ( 16 bit integer ) File access mode word 'r w x -r w x- r w x' (user permission-group permission-others permission) r-read, w-write, x-execute To change the access mode, we use chmod(filename,mode). Example 1: To change mode of myfile to 'rw-rw-r–' (ie. read, write permission for user - read,write permission for group - only read permission for others) we give the args as: chmod(myfile,0664) . Each operation is represented by discrete values 'r' is 4 'w' is 2 'x' is 1 Therefore, for 'rw' the value is 6(4+2). Example 2: To change mode of myfile to 'rwxr–r–' we give the args as: chmod(myfile,0744). Q.What are links and symbolic links in UNIX file system? Ans: A link is a second name (not a file) for a file. Links can be used to assign more than one name to a file, but cannot be used to assign a directory more than one name or link filenames on different computers. Symbolic link 'is' a file that only contains the name of another file.Operation on the symbolic link is directed to the file pointed by the it.Both the limitations of links are eliminated in symbolic links. Commands for linking files are: Link ln filename1 filename2 Symbolic link ln -s filename1 filename2 Q.What is a FIFO? Ans: FIFO are otherwise called as 'named pipes'. FIFO (first-in-first-out) is a special file which is said to be data transient. Once data is read from named pipe, it cannot be read again. Also, data can be read only in the order written. It is used in interprocess communication where a process writes to one end of the pipe (producer) and the other reads from the other end (consumer). Q.How do you create special files like named pipes and device files? Ans: The system call mknod creates special files in the following sequence. 1. kernel assigns new inode, 2. sets the file type to indicate that the file is a pipe, directory or special file, 3. If it is a device file, it makes the other entries like major, minor device numbers. For example: If the device is a disk, major device number refers to the disk controller and minor device number is the disk. Q.Discuss the mount and unmount system calls Ans: The privileged mount system call is used to attach a file system to a directory of another file system; the unmount system call detaches a file system. When you mount another file system on to your directory, you are essentially splicing one directory tree onto a branch in another directory tree. The first argument to mount call is the mount point, that is , a directory in the current file naming system. The second argument is the file system to mount to that point. When you insert a cdrom to your unix system's drive, the file system in the cdrom automatically mounts to /dev/cdrom in your system. Q.How does the inode map to data block of a file? Ans: Inode has 13 block addresses. The first 10 are direct block addresses of the first 10 data blocks in the file. The 11th address points to a one-level index block. The 12th address points to a two-level (double in-direction) index block. The 13th address points to a three-level(triple in-direction)index block. This provides a very large maximum file size with efficient access to large files, but also small files are accessed directly in one disk read. Q.What is a shell? Ans: A shell is an interactive user interface to an operating system services that allows an user to enter commands as character strings or through a graphical user interface. The shell converts them to system calls to the OS or forks off a process to execute the command. System call results and other information from the OS are presented to the user through an interactive interface. Commonly used shells are sh,csh,ks etc. Q.Brief about the initial process sequence while the system boots up. While booting, special process called the 'swapper' or 'scheduler' is created with Process-ID 0. The swapper manages memory allocation for processes and influences CPU allocation. The swapper inturn creates 3 children: the process dispatcher, vhand and dbflush with IDs 1,2 and 3 respectively. This is done by executing the file /etc/init. Process dispatcher gives birth to the shell. Unix keeps track of all the processes in an internal data structure called the Process Table (listing command is ps -el). Q.What are various IDs associated with a process? Ans: Unix identifies each process with a unique integer called ProcessID. The process that executes the request for creation of a process is called the 'parent process' whose PID is 'Parent Process ID'. Every process is associated with a particular user called the 'owner' who has privileges over the process. The identification for the user is 'UserID'. Owner is the user who executes the process. Process also has 'Effective User ID' which determines the access privileges for accessing resources like files. getpid() -process id getppid() -parent process id getuid() -user id geteuid() -effective user id Q.Explain fork() system call. Ans: The `fork()' used to create a new process from an existing process. The new process is called the child process, and the existing process is called the parent. We can tell which is which by checking the return value from `fork()'. The parent gets the child's pid returned to him, but the child gets 0 returned to him. Q.Predict the output of the following program code main() { fork(); printf("Hello World!"); } Answer: Hello World!Hello World! Explanation: The fork creates a child that is a duplicate of the parent process. The child begins from the fork().All the statements after the call to fork() will be executed twice.(once by the parent process and other by child). The statement before fork() is executed only by the parent process. Q.Predict the output of the following program code main() { fork(); fork(); fork(); printf("Hello World!"); } Answer: "Hello World" will be printed 8 times. Explanation: 2^n times where n is the number of calls to fork() Q.List the system calls used for process management: Ans: System calls Description fork() To create a new process exec() To execute a new program in a process wait() To wait until a created process completes its execution exit() To exit from a process execution getpid() To get a process identifier of the current process getppid() To get parent process identifier nice() To bias the existing priority of a process brk() To increase/decrease the data segment size of a process. Q.How can you get/set an environment variable from a program? Ans: Getting the value of an environment variable is done by using `getenv()'. Setting the value of an environment variable is done by using `putenv()'. Q.How can a parent and child process communicate? Ans: A parent and child can communicate through any of the normal inter-process communication schemes (pipes, sockets, message queues, shared memory), but also have some special ways to communicate that take advantage of their relationship as a parent and child. One of the most obvious is that the parent can get the exit status of the child. Q.What is a zombie? Ans: When a program forks and the child finishes before the parent, the kernel still keeps some of its information about the child in case the parent might need it - for example, the parent may need to check the child's exit status. To be able to get this information, the parent calls `wait()'; In the interval between the child terminating and the parent calling `wait()', the child is said to be a `zombie' (If you do `ps', the child will have a `Z' in its status field to indicate this.) Q.What are the process states in Unix? Ans: As a process executes it changes state according to its circumstances. Unix processes have the following states: Running : The process is either running or it is ready to run . Waiting : The process is waiting for an event or for a resource. Stopped : The process has been stopped, usually by receiving a signal. Zombie : The process is dead but have not been removed from the process table. Q.What are MySQL transactions? Ans: A set of instructions/queries that should be executed or rolled back as a single atomic unit. Explain multi-version concurrency control in MySQL. Each row has two additional columns associated with it - creation time and deletion time, but instead of storing timestamps, MySQL stores version numbers. Explain MySQL locks. Table-level locks allow the user to lock the entire table, page-level locks allow locking of certain portions of the tables (those portions are referred to as tables), row-level locks are the most granular and allow locking of specific rows. Explain MySQL architecture. The front layer takes care of network connections and security authentications, the middle layer does the SQL query parsing, and then the query is handled off to the storage engine. A storage engine could be either a default one supplied with MySQL (MyISAM) or a commercial one supplied by a third-party vendor (ScaleDB, InnoDB, etc.) Q.List the main applications of 8 bit microprocessors? Ans: 8 bit microprocessors are used in a variety of applications such as appliances , automobiles ,industrial process and control applications. Q.What is NV-RAM? Ans: Nonvolatile Read Write Memory, also called Flash memory. It is also know as shadow RAM Q.Can ROM be used as stack? Ans: ROM cannot be used as stack because it is not possible to write to ROM. Q.What is stack? Ans: Stack is a portion of RAM used for saving the content of Program Counter and general purpose registers. Q.What is flag? Ans: Flag is a flip-flop used to store the information about the status of a processor and the status of the instruction executed most recently Q.Which processor structure is pipelined? Ans: All x86 processors have pipelined structure. Q.What is a compiler? Ans: Compiler is used to translate the high-level language program into machine code at a time. It doesn’t require special instruction to store in a memory, it stores automatically. The Execution time is less compared to Interpreter. Q.Differentiate between RAM and ROM? Ans: RAM: Read / Write memory, High Speed, Volatile Memory. ROM: Read only memory, Low Speed, Non Voliate Memory. Q.Which transistor is used in each cell of EPROM? Ans: Floating .gate Avalanche Injection MOS (FAMOS) transistor is used in each cell of EPROM. Q.What is called .Scratch pad of computer.? Ans: Cache Memory is scratch pad of computer. Q.What is cache memory? Ans: Cache memory is a small high-speed memory. It is used for temporary storage of data & information between the main memory and the CPU (center processing unit). The cache memory is only in RAM. Q.What is interrupt? Ans: Interrupt is a signal send by external device to the processor so as to request the processor to perform a particular work. Q.Difference between static and dynamic RAM? Ans: Static RAM: No refreshing, 6 to 8 MOS transistors are required to form one memory cell, Information stored as voltage level in a flip flop. Dynamic RAM: Refreshed periodically, 3 to 4 transistors are required to form one memory cell, Information is stored as a charge in the gate to substrate capacitance. Q.What is the difference between primary & secondary storage device? Ans: In primary storage device the storage capacity is limited. It has a volatile memory. In secondary storage device the storage capacity is larger. It is a nonvolatile memory. Primary devices are: RAM / ROM. Secondary devices are: Floppy disc / Hard disk. Q.Why does microprocessor contain ROM chips? Ans: Microprocessor contain ROM chip because it contain instructions to execute data. Q.What is meant by LATCH? Ans: Latch is a D- type flip-flop used as a temporary storage device controlled by a timing signal, which can store 0 or 1. The primary function of a Latch is data storage. It is used in output devices such as LED, to hold the data for display. Q.What is the difference between microprocessor and microcontroller? Ans: In Microprocessor more op-codes, few bit handling instructions. But in Microcontroller: fewer op-codes, more bit handling Instructions, and also it is defined as a device that includes micro processor, memory, & input / output signal lines on a single chip. Q.What is the disadvantage of microprocessor? Ans: It has limitations on the size of data. Most Microprocessor does not support floating-point operations. Q.Is the data bus is Bi-directional? Ans: The data bus is Bi-directional because the same bus is used for transfer of data between Micro Processor and memory or input / output devices in both the direction. Q.Is the address bus unidirectional? Ans: The address bus is unidirectional because the address information is always given by the Micro Processor to address a memory location of an input / output devices. Q.Define HCMOS? Ans: High-density n- type Complimentary Metal Oxide Silicon field effect transistor. Q.What is 1st / 2nd / 3rd / 4th generation processor? Ans: The processor made of PMOS / NMOS / HMOS / HCMOS technology is called 1st / 2nd / 3rd / 4th generation processor, and it is made up of 4 / 8 / 16 / 32 bits. Q.Why 8085 processor is called an 8 bit processor? Ans: Because 8085 processor has 8 bit ALU (Arithmetic Logic Review). Similarly 8086 processor has 16 bit ALU. Q.Give examples for 8 / 16 / 32 bit Microprocessor? Ans: 8-bit Processor - 8085 / Z80 / 6800; 16-bit Processor - 8086 / 68000 / Z8000; 32-bit Processor - 80386 / 80486. Q.What is a Microprocessor? Ans: Microprocessor is a program-controlled device, which fetches the instructions from memory, decodes and executes the instructions. Most Micro Processor is single- chip devices. Q.What command would you use to create an empty file without opening it to edit it? Ans: You use the touch command to create an empty file without needing to open it. Answers a and e point to invalid commands, though either of these might actually be aliased to point to a real command. Answers b and c utilize editors, and so do not satisfy the requirements of the question. actually touch is used to change the timestamps of a file if its exits, otherwise a new file with current timestamps will be created Q.Which of the following commands can you use to cleanly restart a Linux machine? Ans: The commands used to restart a Linux box are shutdown -r, reboot, and init 6. Answers c and e are incorrect. Both of these are used to shut down a Linux box, not restart it. init 6 command is used to restart the Linux machine . Q.What do you type to stop a hung process that resists the standard attempts to shut it down? Ans: The kill command by itself tries to allow a process to exit cleanly. You type kill -9 PID, on the other hand, to abruptly stop a process that will not quit by any other means. Also, pressing Ctrl+C works for many programs. Answers b and d are only valid in some contexts, and even in those contexts will not work on a hung process. Q.Which command do you use to change run levels? Ans: The command used to change run levels is init. Answers a, c, and d point to invalid commands. Answer b is a valid command, but does not set the current run level. The run level command displays the current run level, and the one that was used directly before entering this one. Q.Which two commands can you use to delete directories ? Ans: You can use rmdir or rm -rf to delete a directory. Answer a is incorrect, because the rm command without any specific flags will not delete a directory, it will only delete files. Answers d and e point to a non-existent command. Q.What would you type to send the last 20 lines of a text file to STDIN? Ans: Use the command tail -20 filename to see the last 20 lines of a file. The answers for a and d both point to an invalid command. The answer for b points to a valid command. Typing this answer in with a valid file name will even give you some output. However, the last command tells you who is logged in, it does not actually list the contents of any file named in the command. The answer for c, the head command, is used to look at the beginning of a file, not the end. last choice will be correct answer because only tail command is used to see the last content of any file by default it take 10 line Q.Which daemon controls the network service -> POP3 mail service? Ans: The intend super daemon controls the POP3 mail service. The POP3 mail service runs through the super daemon, not on its own. Answers c and e point to nonexistent, or at least nonstandard daemons. Answer d points to the Usenet news daemon. Q.Who owns the data dictionary? Ans: The SYS user owns the data dictionary. The SYS and SYSTEM users are created when the database is created. The SYS user owns the data dictionary. The SYS and SYSTEM users are created when the database is created. how we can configure sata hard derive during redhat 9 installation. Have the data driver on a floppy drive. At the start of installation, when u boot from the CD/DVD, on the prompt, write “dd”. It will ask for the driver floppy later on and will load the sata driver. Then you can configure/partition the drive using disk druid or fdisk Q.What is difference between AT and CRON? Ans: Cron command is used to schedule the task daily at the same time repeatedly ,”at” command is used to schedule the task only once i.e. to run only one time. Q.What is difference between user right and user permission? Ans: user rights:user rights is that user is authorized to used password. if his password/file/dir is expired he is not able to login user permission:permission is user is permitted to use file/directory. that is authentication if he is authentication for particular file or not. it might be true as per my suggestion. Q.What is the real mean of DHCP? Ans: Dynamic addressing simplifies network administration because the s/w keeps track of IP addresses rather than requiring an administrator to manage the task. That means new computer can be added to the network without any risk of manually assigning unique IP address. Describe the boot process of your favorite Linux in as much detail as you can. Boot process takes place in 4 scenes with 4 main characters. Scene 1 when the computer is switched on, it automatically invokes BIOS.The BIOS will start the processor and perform a POST to check whether the connected device are ready to use and are working properly. Once the POST is completes BIOS will jump to a specified location in the RAM and check for the booting device. The boot sector is always the first sector of the hard disk and BIOS will load the MBR into the memory. Scene 2 Here the boot loader takes the control of the booting process.LILO or GRUB is the boot loaders commonly available. It will help the user to select various boot options. Depending on the boot option selected the kernel is loaded. scene 3 After kernel is loaded the kernel will take the control of the booting process and it will initialize all the hardwares including I/O processors etc.kernel then creates a root device and mounts the partitions. Scene 4 INIT is loaded. How to install 8139 realtek drivers in rhel5.0$ Please help me out. Download the driver from internet. then just unzip the tarball using tar -zxvf then for first compile it using make and make install For proper installation of the driver read the INSTALL / README file given in the tarball. Q.You are debugging a new application that is crashing. You want to watch the messages as they are being written to the log. What command should you use? Ans: The tail command allows you to keep a log open and see each new message as it is written to the log. Q.Which of the following tasks cannot be accomplished with the touch command? Ans: The touch command is usually used to modify either a file’s access or modification time. It can also be used to create a new file. Q.You want to copy the user’s home directories to a new location. Which of the following commands will accomplish this? Ans: The -r option tells the cp command to recurs the directories. The -P option retains the original permissions. Q.You read an article that lists the following command: dd if=/dev/fd0 bs=512 of=/new What does this accomplish? Ans: The dd command is a special copy command often used for floppy disks and tapes. The if= option specifies the source; the bs= is the block size; and the of= option is the output. Q.You attempt to delete a file called sales.mem using the rm command but the command fails. What could be the problem? Ans: In order to delete a file, you must have write rights to the directory containing the file. Linux Interview Questions Linux Interview Questions and Answers Q.You want to search for sale and sales. What regular expression should you use? Ans: Use the asterick (*) to match to zero or more characters. The ‘$’ matches to any one character so sale$ would not find sale. Q.You have a file named ‘kickoff’ and would like to find every line beginning with a number. Which of the following commands will accomplish this? Ans: The command grep ^ kickoff will cause grep to search the file kickoff for any line beginning with a digit. Q.You want to know how many lines in the kickoff file contains ‘prize’. Which of the following commands will produce the desired results? Ans: Using the -c option with the grep command will show the total number of lines containing the specified pattern rather than displaying the lines containing the pattern. Q.You want to verify which lines in the file kickoff contain ‘Bob’. Which of the following commands will accomplish this? Ans: The -n option when used with sed prints only the lines containing the pattern. In this case, the pattern is ‘Bob’ and the file to be searched is kickoff. Q.You have a file called docs.Z but do not know what it is. What is the easiest way to look at the contents of the file? Ans: The .Z extension indicates that this is a file that has been compressed using the compress utility. The zcat utility provides the ability to display the contents of a compressed file. Q.You want to make it possible for your users to mount floppy disks. What do you need to do? Ans: If you add the user option to the line in the fstab file that defines how to mount your CD-ROM, then your users will be able to mount it. What is contained in the directory The /proc directory is a virtual file system that contains system information. Q.After copying a file to a floppy disk, what should you do before removing the disk? Ans: If you do not unmount the floppy before removing it, the files on the floppy may become corrupted. Q.You have set quotas for all your users but half of your users are using more space than they have been allotted. Which of the following could be the problem? Ans: Quotas are set on a partition by partition basis. If your users have home directories on different partitions, you will need to configure quotas for each partition. Q.What command should you use to check the number of files and disk space used and each user’s defined quotas? Ans: The repquota command is used to get a report on the status of the quotas you have set including the amount of allocated space and amount of used space. Q.you have a large spreadsheet located in the /data directory that five different people need to be able to change. How can you enable each user to edit the spreadsheet from their individual home directories? Ans: By creating a link to the file in each user’s home directory, each user is able to easily open and edit the spreadsheet. Also, any changes that are made are seen by all the users with access. Q.You have a file called sales data and create symbolic links to it in bob’s home directory. Bob calls you and says that his link no longer works. How can you fix the link? Ans: Because the link in bob’s directory is a symbolic link, if the file sales data in the /data directory is deleted, the symbolic link will no longer work. Q.You have two files in two different directories with the same inode. What type of link is involved? Ans: Hard links all have the same inode number, unlike symbolic links. Q.You need to locate a file called sales data that one of your user’s created in his home directory but you do not know which one. How could you use the find command to locate this file? Ans: When using the find command to locate a file by name you must specify the starting place in the directory hierarchy and the -name option to specify the file to search for. Q.However, when Bob attempts to open the file he is unsuccessful. What command do you need to use to give Bob ownership of the file? Ans: The chown command can be used by root to give ownership of a file to any user. Q.What is meant by sticky bit? Ans: When the sticky bit is set on a world writable directory, only the owner can delete any file contained in that directory. Q.Your default umask is 002. What does this mean? Ans: The digits of your umask represent owner, group and others in that order. The 0 gives read and write for files and the 2 gives read only for files. Q.Which of the following commands will replace all occurrences of the word rate with the word speed in the file racing? Ans: When using sed to do a search and replace, its default action is to only replace the first occurrence in each line. Adding the ‘g’ makes sed replace all occurrences of the search term even when it occurs multiple times on the same line. Q.You have a tab delimited file called phonenos and want to change each tab to four spaces. What command can you use to accomplish this? Ans: By default, expand converts tabs to eight spaces. Use the -t option to change this behavior. Q.You issue the command head *. What would the resulting output be? Ans: If the number of lines to display is not specified, the first ten lines of the specified file are displayed. The asterick tells head to display the content of each file in the present working directory. Q.what text filter can you use to display a binary file in octal numbers? Ans: The od text filter will dumpt the contents of a file and display it in 2-byte octal numbers. Q.What would be the result of the command paste -s dog cat ? Ans: The paste text filter usually joins two files separating the corresponding lines with a tab. The -s option, however, will cause paste to display the first file, dog, then a new line character, and then the file cat. Q.You wish to print the file vacations with 60 lines to a page. Which of the following commands will accomplish this? Ans: The default page length when using pr is 66 lines. The -l option is used to specify a different length. Q.What would be the result of issuing the command cat phonenos? Ans: The tac text filter is a reverse cat. It displays a file starting with the last line and ending with the first line. Q.You need to see the last fifteen lines of the files dog, cat and horse. What command should you use? Ans: The tail utility displays the end of a file. The -15 tells tail to display the last fifteen lines of each specified file. Q.You have the file phonenos that contains telephone numbers and names separated by a comma. You want to change each comma to a semicolon. Which of the following will accomplish this? Ans: The tr utility is used to replace one string by another. Here the input for tr is provided by the cat command and the commas are all replaced by semicolons. Q.If you type the command cat dog > cat what would you see on your display? Ans: When you use > for redirection, it only effects the standard output. Any messages sent to standard error would still appear on your display. Q.Which first-level segment of the file system contains a majority of system and server configuration files within its subdirectories? Ans: The /etc portion of the file system contains a number of system and daemon configuration files. Answers a, c, d, and e are valid first-level directories, but are incorrect. The /var directory contains items that change on a regular basis, such as log files and print and mail spool directories. The /bin directory contains system binaries, whereas the /sbin directory contains binaries that run with SUID privileges or as a specific user. The /lib directory contains system libraries, both shared and non-shared. Q.What command allows you to set a processor-intensive job to use less CPU time? Ans: The nice command is used to change a job’s priority level, so that it runs slower or faster. Answers a, d, and e are valid commands but are not used to change process information. Answer c is an invalid command. Q.Which of the following commands can be used to get information about a package? Ans: The man command pulls up man pages, the info command pulls up texinfo pages which have replaced the man pages for some packages, and the apropos command helps you to find related commands. Answers b and e are not methods of getting information about a package Where is a good place to store shell scripts that are for use by the author It is best to keep scripts meant only for your account under ~/bin. Answers b, c, d, and e are all valid locations, but not the best places to keep user-specific scripts. Which hardware considerations should you keep in mind when putting together this mail server’s list of components$ A mail server benefits from a large amount of RAM, a fast CPU, and large amounts of fast-access hard drive space. The reason it benefits from having a lot of memory is that it can then handle groups of mail messages all at once. A fast CPU helps it move through processes more quickly, especially when it comes to generating postings to large mailing lists. Having a lot of hard drive space ensures that the mail spool will not run out of free room. Answers a and c are unimportant on a machine that is meant to provide mail service. A Linux box serving such a purpose would only be slowed down with a GUI running, and the GUI is the reason to be concerned with both the monitor resolution and video RAM. Q.Of the following technologies, which is considered a client-side script? Ans: JavaScript is the only client-side script listed. Java and C++ are complete programming languages . Active Server Pages are parsed on the server with the results being sent to the client in HTML. Q.What type of server is used to remotely assign IP addresses to machines during the installation process? Ans: You can use a DHCP server to assign IP addresses to individual machines during the installation process. Answers a, b, d, and e list legitimate Linux servers, but these servers do not provide IP addresses. The SMB, or Samba, tool is used for file and print sharing across multi-OS networks . An NFS server is for file sharing across Linux net-works. FTP is a file storage server that allows people to browse and retrieve information by logging in to it, and HTTP is for the Web Q.What type of local file server can you use to provide the distribution installation materials to the new machine during a network installation? Ans: You can use an NFS server to provide the distribution installation materials to the machine on which you are performing the installation. Answers a, b, c, and d are all valid items but none of them are file servers. Inetd is the superdaemon which controls all intermittently used network services. The FSSTND is the Linux File System Standard. DNS provides domain name resolution, and NNTP is the transfer protocol for usenet news. Q.Which password package should you install to ensure that the central password file couldn’t be stolen easily? Ans: The shadow password package moves the central password file to a more secure location. Answers a, b, and e all point to valid packages, but none of these places the password file in a more secure location. Answer d points to an invalid package. Q.Which command works in almost all distributions to create a boot disk ? Ans: The mkbootdisk command creates a boot disk. Answers b and c are incorrect. The make package is used to compile software, not create boot disks. Answers a and d point to invalid commands. Q.What happens to your ipchains settings when you reboot a machine? Ans: They cannot be automatically saved unless you do something like make an alias for the shutdown routine that ensures this happens. Settings for ipchains are lost during a reboot or shutdown and there is no “setting” to ensure they are automatically saved. Answers a, b, and c are completely incorrect. Answer e is incorrect, but you can save them by hand if you choose to. Q.Which package provides secure remote login sessions, such as secure telnet logins? Ans: The ssh package allows you to configure secure telnet sessions and other remote logins. Answer a points to an invalid package. Answer c points to a valid package, but shadow handles passwords, not data encryption. Answers d and e point to firewalling packages, which regulate what passes in and out of a LAN, but do not handle data encryption. Q.Which package can you use to regulate which network traffic is allowed to enter a specific machine, but not on any other machines? Ans: The tcp_wrappers package is used to regulate the TCP/IP network traffic coming in and out of a machine. Answers b and c both point to valid firewalling packages, but these packages are used for an entire LAN, not just one machine. Answer d points to the commun-ications protocol used to transmit data over the Internet. Answer e points to an invalid package. Q.What type of server is used to remotely assign IP addresses to machines during the installation process? Ans: you can use a DHCP server to assign IP addresses to individual machines during the installation process. Answers a, b, d, and e list legitimate Linux servers, but these servers do not provide IP addresses. The SMB, or Samba, tool is used for file and print sharing across multi-OS networks. An NFS server is for file sharing across Linux net-works. FTP is a file storage server that allows people to browse and retrieve information by logging in to it, and HTTP is for the Web Q.Which partitioning tool is available in all distributions? Ans: The fdisk partitioning tool is available in all Linux distributions. Answers a, c, and e all handle partitioning, but do not come with all distributions. Disk Druid is made by Red Hat and used in its distribution along with some derivatives. Partition Magic and System Commander are tools made by third-party companies. Answer d is not a tool, but a file system type. Specifically, FAT32 is the file system type used in Windows 98. Which first-level segment of the file system contains a majority of system The /etc portion of the file system contains a number of system and daemon configuration files. Answers a, c, d, and e are valid first-level directories, but are incorrect. The /var directory contains items that change on a regular basis, such as log files and print and mail spool directories. The /bin directory contains system binaries, whereas the /sbin directory contains binaries that run with SUID privileges or as a specific user. The /lib directory contains system libraries, both shared and non-shared. Q.Which file do you edit to set partitions to mount at boot time? Ans: The file /etc/fstab manages which partitions are automatically mounted onto the file system. Answers b and c refer to valid items, but they are not used to manage the file system. The file /etc/services maps networking services to the ports they utilize, and /etc/smb.conf is the configuration file for the Samba service. Answers d and e point to files that do not exist. Q.Which first-level segment of the file system contains a majority of system and server configuration files within its subdirectories? Ans: The /etc portion of the file system contains a number of system and daemon configuration files. Answers a, c, d, and e are valid first-level directories, but are incorrect. The /var directory contains items that change on a regular basis, such as log files and print and mail spool directories. The /bin directory contains system binaries, whereas the /sbin directory contains binaries that run with SUID privileges or as a specific user. The /lib directory contains system libraries, both shared and non-shared. Q.Which file do you edit to set partitions to mount at boot time? Ans: The file /etc/fstab manages which partitions are automatically mounted onto the file system. Answers b and c refer to valid items, but they are not used to manage the file system. The file /etc/services maps networking services to the ports they utilize, and /etc/smb.conf is the configuration file for the Samba service. Answers d and e point to files that do not exist. Q.Which shell do you assign to a POP3 mail-only account? Ans: You assign a POP3 only account to the /bin/false shell. Answers b and c both point to the same shell, the bash shell. However, assigning this shell to a POP3 only user gives him or her login access, which is what you are trying to avoid. Answers d and e are both invalid options in a standard setup. Q.What command would you use to create an empty file without opening it to edit it? Ans: You use the touch command to create an empty file without needing to open it. Answers a and e point to invalid commands, though either of these might actually be aliased to point to a real command. Answers b and c utilize editors, and so do not satisfy the requirements of the question. actually touch is used to change the timestamps of a file if its exits, otherwise a new file with current timestamps will be created Q.Which command do you use to change run levels? Ans: The command used to change run levels is init. Answers a, c, and d point to invalid commands. Answer b is a valid command, but does not set the current run level. The run level command displays the current run level, and the one that was used directly before entering this one. Q.Which daemon controls the network service -> POP3 mail service? Ans: The inetd superdaemon controls the POP3 mail service. The POP3 mail service runs through the superdaemon, not on its own. Answers c and e point to nonexistent, or at least nonstandard daemons. Answer d points to the Usenet news daemon. Q.Who owns the data dictionary ? Ans: The SYS user owns the data dictionary. The SYS and SYSTEM users are created when the database is created. The SYS user owns the data dictionary. The SYS and SYSTEM users are created when the database is created. how we can configure sata hard derive during redhat 9 installation. Have the data driver on a floppy drive. At the start of installation, when u boot from the CD/DVD, on the prompt, write “dd”. It will ask for the driver floppy later on and will load the sata driver. Then you can configure/partition the drive using disk druid or fdisk. Q.What is difference between AT and CRON? Ans: cron can be set only for a particular time but at is used to schedule and execute Contact Author Contact Author Cron command is used to schedule the task daily at the same time repeatedly ,”at” command is used to schedule the task only once i.e. to run only one time. Q.What is difference between user right and user permission? Ans: user rights:user rights is that user is authorized to used password. if his password/file/dir is expired he is not able to login user permission:permission is user is permitted to use file/directory. that is authentication if he is authentication for particular file or not. it might be true as per my suggestion. Q.What is the real mean of DHCP? Ans: dynamic Host Configuration Protocol(DHCP) is a protocol used by networked devices (clients) to obtain the IP address. Contact Author Contact Author Dynamic addressing simplifies network administration because the s/w keeps track of IP addresses rather than requiring an administrator to manage the task. That means new computer can be added to the network without any risk of manually assigning unique IP address. Describe the boot process of your favorite Linux in as much detail as you can. Booting process : first BIOS loads the boot loaders, then boot loaders loads the kernel ,then kernel mount the file systems and drivers installation will takes place and in it will be loaded. How to install 8139 realtek drivers in rhel5.0$ Please help me out. Download the driver from internet. then just unzip the tarball using tar -zxvf then for first compile it using make and make install For proper installation of the driver read the INSTALL / README file given in the tarball. Q.What is difference between user right and user permission? Ans: user rights:user rights is that user is authorized to used password. if his password/file/dir is expired he is not able to login user permission:permission is user is permitted to use file/directory. that is authentication if he is authentication for particular file or not. it might be true as per my suggestion. Q.What is the real mean of DHCP? Ans: Dynamic addressing simplifies network administration because the s/w keeps track of IP addresses rather than requiring an administrator to manage the task. That means new computer can be added to the network without any risk of manually assigning unique IP address. Q.Describe the boot process of your favorite Linux in as much detail as you can? Ans: Boot process takes place in 4 scenes with 4 main characters. Scene 1 when the computer is switched on, it automatically invokes BIOS.The BIOS will start the processor and perform a POST to check whether the connected device are ready to use and are working properly. Once the POST is completes BIOS will jump to a specified location in the RAM and check for the booting device. The boot sector is always the first sector of the hard disk and BIOS will load the MBR into the memory. Scene 2 Here the boot loader takes the control of the booting process.LILO or GRUB is the boot loaders commonly available. It will help the user to select various boot options. Depending on the boot option selected the kernel is loaded. scene 3 After kernel is loaded the kernel will take the control of the booting process and it will initialize all the hardwares including I/O processors etc.kernel then creates a root device and mounts the partitions. Scene 4 INIT is loaded. Q.What is the minimum number of partitions you need to install Linux? What command can you use to review boot messages? Ans: 1. Three Partition. boot partition, swap partition and root partition, these are the minimum partitions to install the Linux. dmesg or /var/log/messages What command you execute to display the last five commands you have entered$ Which partitions might you creates on mail server HDDs other than the root, swap and boot partitions$ Which partitioning tool is available in all distributions$ Which two commands can you use to delete directories$ Which file defines all users on your system$ history|tail -5 /var fdisk, parted rm, rmdir /etc/passwd Q.How to install 8139 realtek drivers in rhel5.0? Please help me out? Ans: Download the driver from internet. then just unzip the tarball using tar -zxvf then for first compile it using make and make install For proper installation of the driver read the INSTALL / README file given in the tarball. Q.What does Security-enhanced Linux give me that standard Linux can’t? Ans: The Security-enhanced Linux kernel enforces mandatory access control policies that confine user programs and system servers to the minimum amount of privilege they require to do their jobs. When confined in this way, the ability of these user programs and system daemons to cause harm when compromised (via buffer overflows or misconfigurations, for example) is reduced or eliminated. This confinement mechanism operates independently of the traditional Linux access control mechanisms. It has no concept of a “root” super-user, and does not share the well-known shortcomings of the traditional Linux security mechanisms (such as a dependence on setuid/setgid binaries).The security of an unmodified Linux system depends on the correctness of the kernel, all the privileged applications, and each of their configurations. A problem in any one of these areas may allow the compromise of the entire system. In contrast, the security of a modified system based on the Security-enhanced Linux kernel depends primarily on the correctness of the kernel and its security policy configuration. While problems with the correctness or configuration of applications may allow the limited compromise of individual user programs and system daemons, they do not pose a threat to the security of other user programs and system daemons or to the security of the system as a whole. Q.What is SELinux? Ans: SELinux Security-enhanced Linux is a research prototype of the Linux® kernel and a number of utilities with enhanced security functionality designed simply to demonstrate the value of mandatory access controls to the Linux community and how such controls could be added to Linux. The Security-enhanced Linux kernel contains new architectural components originally developed to improve the security of the Flask operating system. These architectural components provide general support for the enforcement of many kinds of mandatory access control policies, including those based on the concepts of Type Enforcement®, Role-based Access Control, and Multi-level Security. Q.What is the most graceful way to get to run level single user mode? Ans: The most graceful way is to use the command init s. If you want to shut everything down before going to single user mode then do init 0 first and from the ok prompt do a boot -s. Write a command to find all of the files which have been accessed within the last 10 days. The following command will find all of the files which have been accessed within the last 10 days find / -type f -atime -10 > December.files This command will find all the files under root, which is ‘/’, with file type is file. ‘-atime -30′ will give all the files accessed less than 10 days ago. And the output will put into a file call Monthname.files. Q.What is the main advantage of creating links to a file instead of copies of the file? Ans: The main advantage is not really that it saves disk space (though it does that too) but, rather, that a change of permissions on the file is applied to all the link access points. The link will show permissions of lrwxrwxrwx but that is for the link itself and not the access to the file to which the link points. Thus if you want to change the permissions for a command, such as su, you only have to do it on the original. With copies you have to find all of the copies and change permission on each of the copies. Q.What is LILO? Ans: LILO stands for Linux boot loader. It will load the MBR, master boot record, into the memory, and tell the system which partition and hard drive to boot from. Q.What is CVS? Ans: CVS is Concurrent Version System. It is the front end to the RCS revision control system which extends the notion of revision control from a collection of files in a single directory to a hierarchical collection of directories consisting of revision controlled files. These directories and files can be combined together to form a software release. There are some useful commands that are being used very often. They are cvs checkout cvs update cvs add cvs remove cvs commit Q.What is NFS? What is its job? Ans: NFS stands for Network File System. NFS enables filesystems physically residing on one computer system to be used by other computers in the network, appearing to users on the remote host as just another local disk. Q.In Linux OS, what is the file server? Ans: The file server is a machine that shares its disk storage and files with other machines on the network. Q.What are the techniques that you use to handle the collisions in hash tables? Ans: We can use two major techniques to handle the collisions. They are open addressing and separate chaining. In open addressing, data items that hash to a full array cell are placed in another cell in the array. In separate chaining, each array element consists of a linked list. All data items hashing to a given array index are inserted in that list. Q.What is the major advantage of a hash table? Ans: The major advantage of a hash table is its speed. Because the hash function is to take a range of key values and transform them into index values in such a way that the key values are distributed randomly across all the indices of a hash table. Q.What is Write Command ? Ans: The write command enables you to write an actual message on the other terminal online. You have to issue the write command with the login ID of the user with whom you want to communicate. The write command informs the user at the other end that there is a message from another user. write pastes that message onto the other user’s terminal if their terminal’s write permissions are set. Even if they are in the middle of an edit session, write overwrites whatever is on the screen. The edit session contents are not corrupted; you can restore the original screen on most editors with Ctrl-L. write is mostly used for one-way communication, but you can have an actual conversation as well Q.Why You Shouldn’t Use the root Login? Ans: The root login does not restrict you in any way. When you log in as root, you become the system. The root login is also sometimes called the super user login. With one simple command, issued either on purpose or by accident, you can destroy your entire Linux installation. For this reason, use the root login only when necessary. Avoid experimenting with commands when you do log in as root. Q.How big should the swap-space partition be? Ans: Swap space is used as an extension of physical RAM, the more RAM you have, the less swap space is required. You can add the amount of swap space and the amount of RAM together to get the amount of RAM Linux will use. For example, if you have 8MB of RAM on your machine’s motherboard, and a 16MB swap-space partition, Linux will behave as though you had 24MB of total RAM. Q.Which field is used to define the user’s default shell? Ans: command-The last field, called either command or login command, is used to specify what shell the user will use when he logs in. Q.When you create a new partition, you need to designate its size by defining the starting and ending? Ans: cylinders-When creating a new partition you must first specify its starting cylinder. You can then either specify its size or the ending cylinder. Q.What can you type at a command line to determine which shell you are using? Ans: echo $SHELL-The name and path to the shell you are using is saved to the SHELL environment variable. You can then use the echo command to print out the value of any variable by preceding the variable’s name with $. Therefore, typing echo $SHELL will display the name of your shell. Q.In order to display the last five commands you have entered using the fc command, you would type? Ans: fc -5-The fc command can be used to edit or rerun commands you have previously entered. To specify the number of commands to list, use -n. Q.What command should you use to check your file system? Ans: fsck-The fsck command is used to check the integrity of the file system on your disk. Q.What file defines the levels of messages written to system log files? Ans: kernel.h-To determine the various levels of messages that are defined on your system, examine the kernel.h file. Q.What account is created when you install Linux? Ans: root-Whenever you install Linux, only one user account is created. This is the super user account also known as root. Q.What daemon is responsible for tracking events on your system? Ans: Syslogd-The syslogd daemon is responsible for tracking system information and saving it to specified log files. Q.Where standard output is usually directed? Ans: To the screen or display-By default, your shell directs standard output to your screen or display. Q.What utility can you use to show a dynamic listing of running processes? Ans: Top-The top utility shows a listing of all running processes that is dynamically updated Q.Who owns the data dictionary? Ans: The SYS user owns the data dictionary. The SYS and SYSTEM users are created when the database is created. Q.Compare Linux credit based algorithm with other scheduling algorithms? Ans: For the conventional time –shared processes, Linux uses a prioritized, credit-based algorithm. Each process possesses a certain number of scheduling credits; when a new task must be chosen to run, the process with most credits is selected. Every time that a timer interrupt occurs, the currently running process loses one credit; when its credits reaches zero, it is suspended and another process is chosen. If no runnable processes have any credits, then Linux performs a recrediting operation, adding credits to every process in the system (rather than just to the runnable ones), according to the following rule: Credits = credits/2 + priority The above scheduling class is used for time-shared process and the in Linux for the real-time scheduling is simpler it uses scheduling classes: first come, first served (FCFS), and round-robin (RR) .In both cases, each process has a priority in addition to its scheduling class. In time-sharing scheduling, however, processes of different priorities can still compete with one another to some extent; in real-time scheduling, the scheduler always runs the process with the highest priority. Among processes of equal priority, it runs the process that has been waiting longest. The only difference between FCFS and RR scheduling is that FCFS processes continue to run until they either exit or block, whereas a round-robin process will be preempted after a while and will be moved to the end of the scheduling queue, so round-robin processes of equal priority will automatically time share among themselves. Linux’s real-time scheduling is soft-real time rather than hard-real time. The scheduler offers strict guarantees about the relative priorities of real-time processes, but the kernel does not offer any guarantees about how quickly a real-time process will be scheduled once that process becomes runnable. Thus the Linux uses different scheduling classes for time-shared and real-time processes. contact for more on Linux Online Training
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