Interview Questions Linux

This article provides basic Linux interview questions with answers.

What command do you use to format a partition with a file system?

You could use mkfs command to format partition with file system.

Which command will assign IP address 192.168.1.1 and subnet mask 255.255.255.0 to eth0 network interface?

ifconfig command can be used to assign IP address. Following command will do the given task

ifconfig eth0 192.168.1.1 netmask 255.255.255.0

Which option in fdisk will display the partition table?

In fidisk utility, the "p" command will print the partition table.

To create a recurring scheduled task, which Linux scheduling tool should you use?

The cron command allows you to create recurring tasks

What command can you use to enable an Ethernet network interface that has already been configured?

To enable already configured interface use

ifconfig [interface] up

command. For example to up eth0 interface use following command

#ifconfig eth0 up

How will you decompress the demo.tar.gz file?

To decompress use following command

#tar -zxvf demo.tar.gz

A core dump file contains this message, “Program terminated with signal 11, segmentation fault.” What does this message indicate?

The core file will tell you what exactly caused the program to crash. So this message indicate that the program crashed because of a segmentation fault in memory.

What command runs fdisk on the first ATA/IDE hard drive?

The first ATA/IDE hard drive is hda, so the command would be

# fdisk /dev/hda

An application is creating several, very large core dump files. What should the administrator do if he has no intention of debugging these files?

If administrator have no intention of keeping these files for debugging purposes, they should be deleted because they are wasting valuable disk space, and may cause system to run out of space.

When checking the partition information on your hard drive with fdisk, you notice that one of the partitions is formatted as "Linux Swap" and is approximately 512MB in size. What is the purpose of this partition?

The Linux swap file is used for virtual memory to store additional information that cannot fit into current memory. This swap file allows information to be cached on disk, and can be retrieved very quickly. Heavy use of the swap file indicates a low memory condition.

What sort of kernel error can cause a Linux system to crash and write a memory core dump?

Kernel panic error can cause a Linux system to crash. A kernel panic indicates that a kernel process has crashed. This is a very serious error that causes the entire Linux system to crash. These core dumps should be analyzed carefully to find the root cause of the problem.

An administrator wants to assign an IP address of 192.168.1.10, a subnet mask of 255.255.255.0, and a broadcast address of 192.168.1.254 to eth1. What command will accomplish this task?

Following command will do this task

ifconfig eth1 192.168.1.10 netmask 255.255.255.0 broadcast 192.168.1.254

What command should you use to set up a job to run at 11:15 a.m. today?

When you are only running the job once at the specified time, you should always use the at command. In this case following command will do the task

#at 11:15

You are tasked to set up a schedule to perform automatic checks of available disk space at the end of the day. How can you accomplish this task?

To accomplish this task set up cron to run a script that will check the disk space daily at 7:00 p.m. The output will be e-mailed to the root account. You can compare the results from day to day to analyze disk space usage.

Your cron file should look similar to the following:

* 19 * * * df -kl

As a administrator you need to terminate the sendmail process. How will you do that?

First you need to determine the PID of sendmail so it can be killed.

#ps -ef |grep sendmail

Now you can use kill command to terminate the process associated with sendmail.

You noticed a kernel error message during the boot process, but it scrolled before you could read this? What log file could you check to find out that message?

The log file that contains kernel boot messages is /var/log/dmesg.

You execute a command that is going to take a long time. How can you get back to your shell prompt to perform other task?

You can use bg command to send a running process to the background.

You need to kill all instances of Web Server? What command will you execute to do this?

You can use killall httpd command to kill all httpd process. httpd process run web server.

How can you list all running process?

Use ps -ef command to list all running process.

#ps -ef

As a Linux admin you want to know what processes are being run by user sumit. What command can you use ?

You can use #ps -au command to list all the process owned by user. Following command will do the assigned task

#ps -au sumit

Which log file keeps track of all user logins and logouts?

/var/log/wtmp log file keeps track of all user logins and logouts.

What is the first process that is run when a Linux system starts, and is responsible for starting all other system processes and services?

The init process is the first process to be run. It is the parent process of all other Linux system processes, services, and daemons that are needed to run the system.

Which command will you use to bring a process in foreground, which is running in the background?

The fg command immediately moves the program to the foreground.

An administrator has accidentally killed a core process. What is the result of this action?

Killing a core process can potentially crash your system because many critical services rely on these core processes

As a administrator you need to monitor the /var/log/messages file in real time to resolve the issue? How would you do that?

You can use tail command with -f option. Following command will do the assigned task

#tail -f /var/log/messages

From the output of ps command how will you determine the ID number of the parent process of a particular program?

PPID refers to the parent process identification number.

While scanning the /var/log/messages file, you notices an error stating an authentication failure for root. What could this mean?

Any failed login attempts for root are logged into the /var/log/messages file. It indicate that some has tried to login as root.

As an administrator you noticed from top command that an unidentified process is using up all CPU and memory. You suspects that is a user's process that has run away. How should you fix this ?

The process should be immediately killed before it consumes so many resources that the server cannot run properly, and therefore crash.

What command can an administrator use to track real-time information on processes and the resources that they are using?

The top command is used to monitor processes and resources in real-time.

A developer with username sanjay has told you that one or his processes seem to be locked up and he cannot it. He reported that it a bug in his code and may quickly use up all CPU and RAM resources on the server. How will you tack the process and terminate it?

Your first step is to identify the process, use ps command

#ps -au sanjay

Now run top command to compare the process running, and verify which one is using the most resources. After you have identified the problem process, you can use the kill command to terminate it. Because the user was unable to stop the process, you should probably force a kill signal to make sure that the process stops:

#kill -9 [PID of process]

Now, to verify that it has stopped, run the ps command again on the user:

ps -au sanjay