Linux Interview Questions and Answers for Freshers - Solved:

We have prepared a set of questions to help Freshers and Experienced Linux Admins in their preparations for Interview. This list includes Google interview questions for Linux Admin, Amazon interview questions for Linux admin and other reputed firms as well.
You will find these questions very helpful in your Linux Admins interviews. Prepare well and All the very best.

All the feedbacks and suggestions are most welocome.

   1.What is two types of Linux User Mode ?
     Command Line

   2.What is command for created multiple files at a time?

   3.What is INODE and How to Identify?
     Its unique identification code for files and directories, it was generate automatically while creating
     new file and directories
         ls -i filename
         ls -ldi directoryname

   4.List of Permissions and Users
     Read, Write and Execute
     Owner, Group Owners and Others

   5.List of Special Permissions and numerical value.
     Set User ID = 4
     Set Group ID = 2
     Stickybit = 1

   6. What command to use see Process list in Hierarchical Structure along with PID?
      pstree -P

   7. What is use of “top” command and how to sort Memory and User wise?
      Its used to real time monitor hardware utilization of linux machine.
      Press M to sort Memory wise result
      Press U to sort User wise result

   8. What is command for to force close one particular process
      kill -9 Processid

   9.What is command to refresh NIC ?
     Service network restart

   10.Tell me two types of IP Address configuration
      Static IP Address
      Dynamic IP Address

   11.How do Enable / Disable Ethernet Device
      Open and Edit this file #vi /etc/sysconfig/network-scripts/devicename
      For enable ONBOOT = yes
      For disable ONBOOT =no

   12.What is command to change Hostname without System Restart
      hostname newhostname

   13.What is File Path of Network Configuration ?

   14.What is File Path of DNS Configuration ?

   15.How to Update locate DB ?

   16. How to edit and save file using editors?
       The following commands are used to exit from vi editors.
          1. :wq saves the current work and exits the VI.
          2. :q! exits the VI without saving current work.

   17.What is command for Zip and Unzip files
      1. gzip = Compress File
      2. gunzip = Uncompress File

   18.What is file path of Alias name set by Permanent?

   19.What is MBR in linux?
      Its Master Boot Recorder to help booting operating system.

   20.What is Two Types of Mount in linux?
      Temporary Mount
      Permanent Mount

   21.What is command for delete Partition?
     #palimpsest &

   22.What is command for Refresh Partition?
      mount -a

   23.What is SWAP?
      Linux uses swap space to increase the amount of virtual memory available to a host. It can use one or
      more dedicated swap partitions or a swap file on a regular filesystem or logical volume.

   24.What are types can set SWAP?
      Temporary set
      Permanent set

   25. What command use for Filesystem Error checking and Error Fixing
      fsck and e2fsck

   26. What is PV, VG, and LVM
      PV = Physical Volume
      VG = Volume Group
      LVM = Logical Volume

   27. What is LVM
      LVM is used to create logical partitions and during run time we can resize particular partition without
      data loss.
      Empty partitions only can do LVM creation.

   28. What are common commands used for Physical Volume

   29. What command is used for create Volume Group

   30. What is Syntax for LVM Create?
       #lvcreate -L partitionsize -n userdefinename volumegroupname

   31. What types of Installation Tools in REDHAT?
       RPM = Redhat Package Manager
       YUM = Yellow Dog Updated Modifier

   32. Tell me Linux Boot Sequence Floow?
       BIOS → MBR → Boot Loader → Kernal → Runlevel

   33. Types of Zone in DNS?
       Forward lookup zone
       Reverse lookup zone

   34. What are inbuilt firwall in Linux ?
       IP Tables

   35. What command to Execute disable IPTables permanently?
       #iptables -F
       service iptables save

   36. What is SELinux?
       Its one type of firewall in linux
       To block particular service in a Protocol

   37. File to disable SELinux permanently:

   38. What is command to check selinux status ?

   39. What is LDAP
       The Lightweight Directory Access Protocol (LDAP) is a set of open protocols used to access centrally
       stored information over a network.

   40. Which Configuration File Is Required For Ldap Clients?

   41. What Is The Name Of Main Configuration File Name For Ldap Server?

   42. How Will You Verify Ldap Configuration File?
      slaptest -u

   43. What is command package install using YUM without ask Prompt?
       yum install packagename -y

   44. What is command Uninstall package?
       yum remove packagename

   45. What is command package re-install using YUM without ask Prompt?
       yum reinstall packagename -y

   46. Location of Cron file in linux?

   47. What is command for to see Particular user Job Schedule ?
       crontab -lu username

   48. What is command for restart cron service?
       service crond restart

   49. What is command for restart postfix service?
       service postfix restart 50.What is command for FTP service on and restart?
       chkconfig vsftpd on
       service vsftpd restart

   50. What is Kernel un Unix Operating system?
       Kernel is the heart of operating system. It interacts with shell and executes the machine level language.

   51. How can I save my input and output commands and see them when required?
       At the beginning of the session if you use 'script' command then the details of the input and output
       commands will be saved in a file called typescript and we can view it any time using “cat typescript”
       This is very useful to track what user is doing what. HISTORY command will not work because it shows
       data only for the current session.

   52. How to create a file in Unix?
       There are multiple way to create files in unix, but the simple way to create a file is using “cat” and 
       “Touch” command
            cat > File name
            touch file name

   53. How can I check which processes are running in my machine?
       To check process which are running in my machine I can use two commands. (a) TOP and (b) PS

   54. What is the difference between TOP and PS command?
       Top command gives the dynamic view of the processes are running in the server and generally the
       dynamic change happens in every 3 second. Whereas PS commands gives the static view of the processes.

   55. You used TOP command and without aborting the TOP process I need to kill one process. Is it possible to kill?
       Yes TOP command it self has a command prompt. Type K then it will ask you for the PID of the process to
       kill. Hit the PID and enter, it will kill the process.

   56. What is the difference between creating a file in cat and in touch command?
       cat command creates a file and we can save some data inside the file but touch command by default will
       create a blank file.

   57. How can I create multiple directories at a time? Say I want to create a directory D1 and inside that D2 
       and inside that D3. Is it possible? If yes how ?
       Yes, creating multiple directories is possible. In this scenario the below command works.
       #mkdir –p D1/D2/D3

   58. I want to create D1, under that D2 and D3. Inside D2 I want D4 and inside D3 I want D5 to be created. 
       How is it possible?
       The below command will work for it.
         #mkdir –p D1/D2/D4 D1/D3/D5

   59. How can I check in which directory I am in ?
       Use PWD command to check which directory you are in.

   60. We are using so many commands and getting output. Have you ever wondered how the commands are executing 
       and getting you the output?
       Yes, every command in Unix is a C program in the backend. When we type a command and hit enter the program 
       runs in the backend and gives you the output.
       We can view the C program as well as below.
       type <Command Name> ->hit enter, it will give you a path where the program the command is located.
       You can view the program by doing cat and the path name. it will open a C program file in decrypted mode.

   61. How can I list the directories and the files ?
       Using ls command. I can view the directories and files of the system.

   62. How can I view hidden files in a system ?
       Using ls –a command I can view the hidden files of the sytem

   63. In real time environment many people use “ll” command instead of ls. So is there any command called “ll” 
       No, there is no such command called “ll”. It’s just the alias of ls command. We can check it by typing
       alias command.

   64. What is a shell ?
       Description of shell is huge, but yes commonly we explain it as the interpreter between the user and the

   65. Describe the usage of rm –r* command in unix and shall we use it in real time environment?
       rm –r* will remove all the file entries in the current directory. It is not advisable to use this command
       in real time environment. Specifically in production. Because we have huge files which are necessary to be
       accessed by other users.

   66. What is symbolic link ?
       The second name of a file is called a link, it’s assigned to create another link to the current file.

   67. What is absolute path and relative path in unix ?
       Absolute path refers to the path starting from the root directory and the path continues with a sequence
       starting from Root. Whereas relative path is the current path.

   68. How can I check the system IP ?
       type hostname command or else you can use ifconfig as well.

   69. How can I check if a server is up and running or not ?
       you can use ping –t command for this.
       Ping –t <hostname> or <IP address>

   70. How can I append some lines in an existing file ?
       #cat >> file name and hit enter. You can append lines below the existing lines of the file. 
       And do a ctrl D to save and exit.

   71. What is FIFO and LIFO in unix ?
       FIFO is first in first out and LIFO is last in last out.

   72. What is PATH variable ?
       PATH is an environmental variable which contains the path of the command files and we can change the
       paths inside the PATH variable.

   73. How can I kill a process in unix?
       first use PS –ef command and get the PID of the process you want to kill.
       Then use kill -9 <PID_Number> command to kill the process.

   74. How can I check the memory size of a linux/unix machine ?
       Use Free –m or free –G command to check the memory size of a linux machine.

   75. How to check disk utilization of a linux server?
       Use du command to check the disk utilization.

   76. How to check the disk free of all the mount points in unix ?
       use df –h command, it will show the disk free of linux machine.

   77. How can I check who are the users logged in my system?
       use users command. It will how the details of the users logged in to the system.

   78. I have a file Mantu.txt which contains multiple lines and few of the lines has a particular pattern as 
       “India”. I want to print only those lines. How can I ?
       I will ue grep command here. And the syntax will be as below.
       #grep -i “India” Mantu.txt
       grep command is used for pattern earching.

   79. What do you mean by a super user ?
       A admin while giving permission to the users usually give normal access permission but few of the user
       having special permission then normal user, they are called super user.

   80. What is the syntax to move to a super user?
       sudo su – <user name>

   81. How can I change the permission of a file?
       Using chmod command I can change the permissions of a file.

   82. How can I give all permission to a user?
       Use the below command to give all read, write and execute permission.
       chmod 777 <file name>

   83. What is a process group in unix ?
       Collection of more than one process is called as a process group in unix.the function getpgrp returns the
       process group id.

   84. How many numbers are used with kill while killing a process ?
       There are 64 numbers which can be used with kill command but generaly we use kill -9

   85. What are different types of files available in unix?
       There are multiple type of files available in unix, few of among them are :
        • Regular file
        • Image file
        • Binary file
        • Linked file

   86. What are cmp and different command in unix?
       cmp command compares the two files byte by byte and gives the output what is not common in between
       them. Diff command through the output which is not matching between the two file immediately rather
       comparing bit by bit.

   87. What is pipe command ? why it is used for ?
       Pipe symbol interlinks two commands. It stores the output of the first command and give it to the second
       command as input.
         #cat emp.lst | mantu.txt

   88. How can I number the lines of a file in VI editor?
       Open the file using vi <filename>
       Then go to command prompt and type set number. The numbers will be set before every line of the file.

   89. What is the command to check all the options and detail information of a command in unix ?
       We can use man <command name>. it will show you all the possible way to use the command.

   90. What is head command used for ?
       head command is used to view the top portions of the file. Say if you want to view top 5 lines of a file 
       then you can use the below command.
          #cat <filename> | head -5

   91. What is tail command used for ?
       tail command is used to view the bottom of the lines of a file. Say if I want to view bottom 5 lines of a 
       file then I can use the below command.
          #cat <filename> | tail -5

   92. What are the other commands used for pattern searching ?
       grep, awk and sed are the main command used for pattern searching.

   93. How can I search a pattern in vi editor ?
       Open the file with vi. Use /pattern name , then hit enter, it will show you the matching patterns in VI.

   94. How can I delete one line in Vi editor ?
       Use dd in command mode to delete one line of a file in vi.

   95. What is the command used for copying a file?
       Use cp command while copying a file in unix.
         #cp <sourcepath of the file> <destination path of the file>
   96. What is SCP in unix ?
       scp stands for secure copy in unix. The files which get copied by using scp command are decrypted so we
       need not be worry of hacking of the file system.

   97. What is mv command in unix?
       We can move a file or rename a file using this command. General purpose of using mv command is to use
       it for reaming purpose.
   98. What does a touch command do apart from creating a blank file?
       touch command is used to change the access and modification time of the file.

   99. Explain the advantages of executing a process in background
       We use “&” symbol to execute a job in back ground. When we execute a job or process in unix it starts
       executing in the prompt itself and we can’t do other stuffs in the command prompt at that time. So until
       unless the process gets executed we have to seat idle. So for continuous interaction with the command
       prompt we prefer executing the jobs or processes in back ground.

   100. How do you protect file deletion in ext4?
        You change any attributes of the file to read only.
        The command is:
           #chattr +i filename
        And to disable it:
           #chattr -i filename

   101. How do you list the kerenel modules which is already loaded ?
       List Currently Loaded Modules – lsmod
       List Available Kernel Modules – modprobe -l
       Install New modules into Linux Kernel – modprobe vmhghs
       Remove the Currently Loaded Modul – modprobe -r vmhghs

   102. What will happen in chkconfig?
       issuing the command “chkconfig sendmail on” will create symlinks(softlinks)

   103. How To rebuild Corrupted RPM Database ?
        [root@tecmint]# cd /var/lib
        [root@tecmint]# rm __db*
        [root@tecmint]# rpm –rebuilddb
        [root@tecmint]# rpmdb_verify Packages

   104. what resize2fs do at back end?
        Mounted, Extending
        The kernel then begins writing additional filesystem metadata on the newly available storage.
        resize2fs makes the filesystem use only the first size bytes of the storage. It does this by moving both
        filesystem metadata and your data around.
        After the completes, there will be unused storage at the end of the block device, unused by the

   105. Special Permissions in linux
        Sticky bit – Only created user and root can able to delete the file
           #chmod o+t nightwolf.txt
           #chmod +t nightwolf.txt
           #chmod 1777 nightwolf.txt
           #ls -ld nightwolf.txt
           drwxrwxrwt 2 root root 4096 Mar 24 12:19 nightwolf.txt

        SUID – Ging permission for all users like root
        chmod u+s /bin/ls – ls can be used for all users as like root
           # chmod 4555 [path_to_file] 
           #ls -l /bin/ls
            -rwsr-xr-x-x 1 root user 16384 Jan 12 2014 /bin/ls

        SGID – SGUID :- chmod g+s /dir –> all subdirectories and files created inside will get same group
        ownership as the main directory, it doesn’t matter who is creating.
           #chmod 2555 [dir] 
           #ls -l /usr/bin/write
           -r-xr-sr-x 1 root tty 11484 Jan 15 17:55 /usr/bin/write

   106. Password never expire linux?
        # chage -M -1 nightwolf –> set the max passwd age to -1
        # passwd -x -1 nightwolf
        # chage -m 0 -M 99999 -I -1 -E -1 nightwolf

   107. What files are created/modified when adding a user (useradd) in linux?
        /etc/passwd and /etc/shadow
        files from /etc/skel are typically copied into the new user’s home directory

   108. How to see and get info about RAM in your system
        # free
        # cat /proc/meminfo

   109. How will you suspend a running process and put it in the background?

   110. Name the Daemon responsible for tracking System Event on your Linux box?

   111. To see tar file without extracting?
        tar -tvf

   112. How to check dependencies of RPM Package on before Installing ?
        # rpm -qpR BitTorrent-5.2.2-1-Python2.4.noarch.rpm
          python >= 2.3
          python(abi) = 2.4
          python-crypto >= 2.0
          python-twisted >= 2.0
          rpmlib(CompressedFileNames) = 2.6

          q : Query a package
          p : List capabilities this package provides.
          R: List capabilities on which this package depends.

   113. How can we increase disk read performance in single commands?
        To see the current read performance,
         # blockdev –getra /dev/sdb
         # time dd if=/tmp/disk.iso of=/dev/null bs=256k
           2549+1 records in
           2549+1 records out
           copied, 6,84256 seconds, 97,7 MB/s
           real 0m6.845s
           user 0m0.004s
           sys 0m0.865s

        # After test
         # blockdev –setra 1024 /dev/sdb
         # time dd if=/tmp/disk.iso of=/dev/null bs=256k
           2435+1 records in
           2435+1 records out
           copied, 0,364251 seconds, 1,8 GB/s
           real 0m0.370s
           user 0m0.001s
           sys 0m0.370s

   114. How Many Run Levels present in Linux?
        There are seven run levels, with each having its own properties.
         • Halt the system
         • Single-user mode
         • Multiuser mode without networking(NFS)
         • Multi-user mode with text login
         • Not used
         • Multi-user mode with graphical login
         • Reboot

   115. How do i check which NFS version ?
        rpcinfo -p localhost | grep -i nfs
        rpm -qa | grep nfs
        rpm -qi nfs nfs-utils

   116. Use find command to delete file by inode?
        Find and remove file using find command follows:
         # find . -inum 782263 -exec rm -i {} \;

   117. Check if any user is using the file system?
        Check to the what users are currently using the file system:
         # fuser -cu /dev/hdc1
          /opt/backup: 2337c(root)

   118. Explain ntsysv or chkconfig command
        Both are similar
        want all services to start in different runlevel
          # ntsysv –level <level>
          # chkconfig –list <service name>
          # chkconfig <service name> on
          # chkconfig <service name> –level 3

   119. Explained BOOT LOADER?
        The boot loader is then responsible for loading the kernel.
        A boot loader finds the kernel image on the disk, loads it into memory, starts it.
        Stage 1 boot loader:
            First stage the primary boot loader is to find and load the secondary boot loader.
            It will find by looking through the partition table for an active partition.
            This is verified methos to the active partition’s boot record is read from the device into RAM and

        Stage 2 boot loader
            The second-stage, boot loader called the kernel loader.
            The first- and second-stage boot loaders combined are calledGRand Unified Bootloader.
            With stage 2 loaded, GRUB can display a list of available kernels You can select a kernel parameters.

   120. Explained about File System Labels?
        File system labels are useful where you need to address the file system that is on the device.
        The file system label is set, you can use it when mounting the device.
        The name replace to device by LABEL=labelname to do this

        To add a lable on ext3 filesystems
        # mkfs.ext4 -L mylabel /dev/sda2

        To add a lable on exitsting filesystems
        # tune2fs -L mylabel /dev/sda2

   121. To convert ext2 to ext3 filesystem?
        # tune2fs -j /dev/hda4 => Do it on your own risk. I would recommend to create a new filesystem of ext3 
          and copy the data from ext2 to ext3.

   122. To convert ext3 to ext2 filesystem?
        # tune2fs -O^has-journal /dev/hda1 => Do it on your own risk. I would recommend to create a new 
          filesystem of ext2 and copy the data from ext3 to ext2.

   123. To convert ext2 to ext4 filesystem?
        # tune2fs -O dir_index,has_journal,uninit_bg /dev/hdXX
        # e2fsck -pf /dev/hdXX

   124. To convert ext3 to ext4 filesystem?
        umount /dev/sda2
        tune2fs -O extents,uninit_bg,dir_index /dev/sda2
        e2fsck -pf /dev/sda2
        mount /dev/sda2 /home

   125. Explained Hash Tables?
        The bash shell maintains a hash table for each command which has been run. The reason, why it does so
        is, making the commands run faster.
        Whenever, a user runs a command on the shell, it first has to search the command executable as to where
        is it located.
        whenever the first time bash shell, finds the location of a command executable, it adds it to a hash table.
        The next time, same command is run,
        the path is taken from the hash table rather than searched again making the commands run faster.
         # hash
          7 /bin/grep
          1 /usr/bin/which
          1 /usr/bin/touch

       Reset the hash table
        # hash -r

       Delete the corresponding entry
        # hash -d myprint

   126. Following the program will not affected by this shell /sbin/nologin?
        FTP clients
        mail clients
        many setuid programs
        gdm/kdm/xdm (graphical login)

   127. So how do I find out zombie process?
        # ps aux | awk ‘{ print $8 ” ” $2 }’ | grep -w Z
         Z 4104
         Z 5320
         Z 2945

   128. How do I kill zombie process?
        ps axo ppid,stat | grep Z | awk ‘{print $1}’ | xargs kill -HUP
        kill -HUP $(ps -A -ostat,ppid | grep -e ‘[zZ]’| awk ‘{ print $2 }’)
        kill -9 $(ps -A -ostat,ppid | grep -e ‘[zZ]’| awk ‘{ print $2 }’)

   129. Details about Backup?
       • full – as the name implies, this is a backup of everything
       • differential – this is a backup of everything since the last full backup
       • incremental – this is a backup of everything since the last _incremental_ backup

         This command will create a backup of /home and put that in the file /tmp/home.tar
         # tar -cvf /tmp/home.tar /home

        Create a backup of the directories /home /var /root and write that to the file /tmp/system-backup.tar
        # tar -cvf /tmp/system-backup.tar /home /var /root

        The following command makes a backup of /home and writes that to the /dev/mt0 device
        # tar -cvf /dev/mt0 /home

   130. To create a compressed archive of the directory /home
        # tar -zcvf /tmp/home.tar.gz /home
        # tar -jcvf /tmp/home.tar.bz2 /home

   131. Extracts the contents of the compressed file
        # tar -zxvf /file.tar.gz
        # tar -jxvf /file.tar.bz2

   132. To check the contents of a tar file
        # tar -tvf file.tgz

   133. Making Device Backups Using dd
        # dd if=/etc/hosts of=/home/somefile
        # dd if=/etc/passwd of=/home/file1
        # dd if=/dev/sda of=/dev/sdb bs=4096
        # dd if=backup.tar.gz of=/dev/mt0

   134. To save MBR file backup as boot files in tmp directory
        # dd if=/dev/sda of=/tmp/bootfiles bs=512 count=1

   135. Determining Filesystem Usage:
        To determine how much disk space is being used for a given partition, logical volume, or
        NFS mount, use the df command.To display the output in “human readable” format, use the -h argument
        to df.
        The du command displays the disk usage totals for each subdirectory and finally the total usage for
        the current directory.Values are in kilobytes.
        # du -hs /etc
        # du -h /vol1/group1/examplefile

   136. Reporting Disk Performance:
        For example, if the access time for a drive suddenly drops, an administrator
        must quickly start troubleshooting the problem to determine if it is a software or hardware issue or
        simply due to lack of free space on the disk.

   137. Displaying Memory Usage with free
        # free -m
        The free command tells you about current memory usage.
        Two types of system memory exist: physical and virtual. To display the amount of free and used memory,
        both physical and virtual (swap), use the free command

   138. Monitoring and Tuning the Kernel:
        Using the /proc Directory
        Instead of executing utilities such as free and top to determine the status of system resources or fdisk
        to view disk partitions, an administrator can gather system information directly from the kernel through
        the /proc filesystem.
        When you view the contents of files in /proc, you are really asking the kernel what the current state is
        for that particular device or subsystem. To view the contents of a special file in /proc, use the cat, 
        less or more file viewing utilities.

   139. Network Information Service (NIS)
        NIS can have only one authoritative server where the original data files are kept
        This authoritative server is called the master NIS server. If your organization is large enough, you may
        need to distribute the load across more than one machine. This can be done by setting up one or more
        secondary (slave) NIS servers.
        # echo “” >> /etc/sysconfig/network

        # ypserv
          This daemon runs on the NIS server. It listens for queries from clients and responds with answers to
          those queries.

        # ypxfrd
          This daemon is used for propagating and transferring the NIS databases to slave servers.

        # ypbind
          This is the client-side component of NIS. It is responsible for finding an NIS server to be queried
          for information. The ypbind daemon binds NIS clients to an NIS domain. It must be running on any 
          machines running NIS client programs.

   140. Main config file for Yum Server in linux
        # cat /etc/yum.conf
          [main] cachedir=/var/cache/yum

   141. Change User with noLogin Shell:
        # useradd -s /sbin/nologin nightwolf

   142. Add a User with Home Directory, Custom Shell, Custom Comment and UID/GID
        # useradd -m -d /var/www/nightwolf -s /bin/zsh -c “nightwolf web user” -u 1000 -g 1000 nightwolf

   143. Creating a user along with encrypted password in linux
        Encrypt your password using below command
        # openssl passwd -crypt myPa55w0rd

       Now you can use the encrypted the password for your new user
       # useradd -p 4VU5GpOSRWbeo nightwolf

   144. Adding Information to User Account
        # usermod -c “nightwolf user account” nightwolf

   145. Change User Home Directory
        # usermod -d /var/www/ nightwolf

   146. Set User Account Expiry Date
        # usermod -e 2015-03-15 nightwolf

   147. Change User Primary Group
        # usermod -g group_name nightwolf
        set the group_name group as a primary group to the user nightwolf

   148. Adding Group to an Existing User
        # usermod -G nightwolf_test nightwolf
        ‘nightwolf‘ user is added to group called ‘nightwolf_test‘

   149. Change User Login Name
        # usermod -l nightwolf_login_name  nightwolf

   150. Lock User Account
        # usermod -L nightwolf
        you will see a ! added before the encrypted password in /etc/shadow file, means password disabled.

   151. Unlock User Account
        # usermod -U nightwolf

   152. Change User Shell
        # usermod -s /bin/sh nightwolf

   153. Change UID and GID of a User
        # usermod -u 666 -g 777 nightwolf

   154. To check on the status of our RAID device
        # mdadm –query –detail /dev/md0
        # cat /proc/mdstat

   155. To create RAID disk
        # mdadm –create /dev/md0 -l 1 -n 3 /dev/sda{5,6,7}
        # mdadm –create /dev/md0 -l 1 -n 3 /dev/sda /dev/sdb /dev/sdc -x 2 /dev/sdd

   156. To create RAID disk with spare disk
        # mdadm –create /dev/md0 -l 1 -n 2 /dev/sda{5,6,} -x 1 /dev/sda7
        # mdadm –manage /dev/md0 –stop
        # mdadm –create /dev/md0 -l 5 -n 3 /dev/sda{5,6,7} -x 1 /dev/sda8
        x———> spare-devices

   157. To create LVM on RAID 1 disk
        # pvcreate /dev/md0
        # vgcreate datavg /dev/md0
        # lvcreate -L +1G -n /dev/datavg/datalv

   158. Disk Failure on RAID
        To simulate a disk failure, we’ll use mdadm to tell the kernel that /dev/sdb1 has failed
        # mdadm –manage /dev/md0 –fail /dev/sda7
        # cat /proc/mdstat
          sda7 [F]

   159. How do remove failed disk from the RAID array
        # mdadm –manage /dev/md0 –remove /dev/sda7

   160. To add raid device
        # mdadm –manage /dev/md0 –add /dev/sda9

   161. To quickly check the state of all your RAID arrays
        # cat /proc/mdstat

   162. userlist_enable vsftpd
        Will load a list of usernames from the filename specified by the userlist_file directive when this
        option is enabled. And if a user tries to log in using a name in this file, that user will be denied 
        access before even being prompted for a password. The default value is NO.

   163. userlist_deny
        This option is examined if the userlist_enable option is active. When its value is set to NO, users 
        will be denied login, unless they are explicitly listed in the file specified by userlist_file. When
        login is denied, the denial is issued before the user is asked for a password; this helps prevent users
        from sending clear text across the network. The default value is YES.

   163. userlist_file
        This option specifies the name of the file to be loaded when the userlist_enable option is active. The
        default value is vsftpd.user_list.

   164. download_enable
        If set to NO, all download requests will be denied permission. The default value is YES.

   165. write_enable
        This option controls whether any FTP commands that change the file system are allowed.
         These commands are used STOR, DELE, RNFR, RNTO, MKD, RMD, APPE, and SITE.
         The default value is NO.

   166. UserDir
        This directive defines the subdirectory within each user’s home directory, where users
        can place personal content that they want to make accessible via the web server. This
        directory is usually named public_html and is usually stored under each user’s home
        directory. This option is, of course, dependent on the availability of the mod_userdir
        module in the web server setup.
        A sample usage of this option in the httpd.conf file is
        UserDir disable
        UserDir public_html

   167. ErrorDocument
        The ErrorDocuments directive lets you specify what happens when a client asks for  nonexistent document.
        Specifies a file that the server sends when an error of a specific type occurs. You can also provide a
        text message for an error. Here are some examples:
        ErrorDocument 403 “Sorry, you cannot access this directory”
        ErrorDocument 403 /error/noindex.html
        ErrorDocument 404 /cgi-bin/
        ErrorDocument 401 /new_subscriber.htm
        • 400: Bad Request
        • 401: Unauthorized
        • 402: Payment Required
        • 403: Forbidden
        • 404: Not Found
        • 405: Method Not Allowed
        • 406: Not Acceptable
        • 407: Proxy Authentication Required
        • 408: Request Timeout
        • 409: Conflict
        • 410: Gone
        • 411: Length Required
        • 412: Precondition Failed
        • 413: Request Entity Too Large
        • 414: Request-URI Too Long
        • 415: Unsupported Media Type
        • 416: Requested Range Not Satisfiable
        • 417: Expectation Failed
        • 500: Internal Server Error
        • 501: Not Implemented
        • 502: Bad Gateway
        • 503: Service Unavailable
        • 504: Gateway Timeout
        • 505: HTTP Version Not Supported

   168. How to connect to a specific share using smbclient, use the following:
        # smbclient //<servername>/<sharename> -U <username>
        # smbclient // -U nightwolf
        # vim /etc/samba/smb.conf
         hosts allow = <IP addresses>

         valid users: List of Samba users allowed access to the share.

         invalid users: List of Samba users denied access the share. If a user is listed in the
         valid users and the invalid users list, the user is denied access.

         public: If set to yes, password authentication is not required. Access is granted
         through the guest user with guest privileges. (default=no)

         read only: If set to yes, client users can not create, modify, or delete files in the share.(default=yes)

         printable: If set to yes, client users can open, write to, and submit spool files on the shared directory

         hosts allow: List of clients allowed access to share. Use the command man 5 hosts_access for details on 
         valid IP address formats.

         browseable: If set to no, the share will not be visible by a net view or a browse list.

   169. Find Files Using Name in Current Directory?
        # find . -name nightwolf.txt

   170. Find Files Under Home Directory?
        # find /home -name nightwolf.txt

   171. Find all PHP Files in Directory?
        # find . -type f -name “*.php”

   172. Find Files Without 777 Permissions?
        # find / -type f ! -perm 777

   173. Find SGID Files with 644 Permissions?
        # find / -perm 2644

   174. Find Sticky Bit Files with 551 Permissions?
        # find / -perm 1551

   175. Find SUID Files?
        # find / -perm /u=s

   176. Find SGID Files?
        # find / -perm /g=s

   177. Find Read Only Files?
        # find / -perm /u=r

   178. Find Executable Files?
        # find / -perm /a=x

   179. Find all Empty Files?
        # find /tmp -type f -empty

   180. Find all Empty Directories?
        # find /tmp -type d -empty

   181. File all Hidden Files?
        # find /tmp -type f -name “.*”

   182. Find Single File Based on User?
        # find / -user root -name nightwolf.txt

   183. Find all Files Based on User?
        # find /home -user nightwolf

   184. Find all Files Based on Group?
        # find /home -group developer

   185. Find Last 50 Days Modified Files?
        # find / -mtime -50

   186. Find Last 50 Days Accessed Files?
        # find / -atime -50

   187. Find Last 50-100 Days Modified Files?
        # find / -mtime +50 –mtime -100

   188. Find Changed Files in Last 1 Hour?
        # find / -cmin -60

   189. Find Modified Files in Last 1 Hour?
        # find / -mmin -60

   190. Find Accessed Files in Last 1 Hour?
        # find / -amin -60

   191. Find 50MB Files?
        # find / -size 50M

   192. Find using inode number?
        find . -inum 27492358 -exec rm -i {} \;

   193. Main configuration file of Apache server ?

   194. Main configuration file of Apache server ?

   195. Specify number of maximum open files in a single login based on the amount of system RAM.
        # echo “1599383” > /proc/sys/fs/file-max
        This can also be done by using sysctl
        sysctl command is used to change Kernel Parameters at run-time
        # sysctl -w fs.file-max=1599383
        Kernel Parameters can also be changed by making changes in the below file:/etc/sysctl.conf
        Append the below line in the /etc/sysctl.conf file
              fs.file-max = 1599383
        After making the above change run the below command for changes to reflect, loads the sysctl settings
        # sysctl -p

   196. Increase the local port range, by default the port range is small?
         # echo “1024 65535″ > /proc/sys/net/ipv4/ip_local_port_rangeThis can also be done using sysctl command
         # sysctl -w net.ipv4.ip_local_port_range=”1024 65535”
        Append the below line in the /etc/sysctl.conf file
         net.ipv4.ip_local_port_range = 1024 61000
        After making the above change run the below command for changes to reflect, loads the sysctl settings
         # sysctl –p

   197. Disable packet_forwarding(routing)?
        net.ipv4.ip_forward = 0
          # cat /proc/sys/net/ipv4/ip_forward

   198. Mount file systems with noatime options?
        noatime option means it will not update the file and directory access time.
        Main advantage is I/O performance will increase.

   199. Which command is use to extend a logical volume?
          # lvextend –size +<addsize> /dev/<vgname>/<lvname>
          # resize2fs /dev/<vgname>/<lvname>
          # lvextend -L +1G /dev/VolGroup/LogVol1
        This will extend the partition size by +1 GB
          # resize2fs /dev/VolGroup/LogVol1

   200. ServerAdmin : Email address
        This is the e-mail address that the server includes in error messages sent to the client.
        Defines the e-mail address that is shown when the server generates an error page.
        The e-mail address that the Web server provides to clients in case any errors occur.

   201. What is the use of SCP command in Linux?
        SCP command stands for secure copy. It is used to copy/download data from one machine to another machine.

   202. What is telnet and what does it do?
        telnet command is used to check the connectivity to other servers. It helps you to check whether you
        are able to talk to another server or now. Ex: telnet 22 where 22 is the port number.

   203. What is a bastion host?
        A bastion host is also known as a jump server. It is used to connect from one machine to another machine
        securely. Bastion hosts are used to connecting to private servers securely.

   204. What is the command to find the IP address of the host machine in linux?
        You can use ifconfig/ ipaddr show command to find the IP address of the host machine.

   205. Name some of the text editors that are available in Linux?
        Some of the common text editors that are available in Linux are vi/vim, nano, subl, gedit, atom, emacs. Vi
        is the default editor that you have in Linux machines.

   206. What are the different zip files formats that are available in linux?
        The different zip formats in Linux are zip, gzip and bzip.

   207. What is the difference between cp and mv command?
        cp command stands for copy and is used to copy data from one location to another. mv stands for the
        move and is used to move data from one location to another.

   208. How can you run a process in the background in Linux?
        You can run a process in the background by pressing ctrl+z command.

   209. What is the use of ‘chown’ command ?
        chown stands for ‘change ownership’ and is used to change the ownership of a file or directory. Eg:
        chown username.username <filename>.

   210. What is the use of ‘chmod’ command?
        chmod stands for ‘change mode’ and is used to change the permissions on files or directories. Eg: 
          # chmod a+w <filename>

   211. What is the command to create a zip file in linux?
        To create a zip file you can use tar command with -cvzf arguments. Eg: tar -cvzf test.tar.gz <file names
        to be included in the zip>

   212. What is the command to unzip the file in linux?
        To unzip a file you can tar command with -xvzf arguments. Eg: tar -xvzf test.tar.gz

   213. What is the command to show the contents of a zip file ?
        To see the contents of the zip file you can use tar -tvzf arguments. Eg: tar -tvzf test.tar.gz

   214. What is a soft link in Linux?
        A soft link is used to create a shortcut in Linux. This is similar to creating a shortcut in windows systems.

   215. What is the command used to create a soft link?
        To create a soft link you can use ln command with -s arguments. Eg: ln -s /var/www/html html, where
        /var/www/html is the source file and HTML is the destination of the shortcut.

   216. What is the command to remove the soft link in Linux?
        To remove the soft link in Linux you can use unlink command. Eg: unlink <filename>

   217. What is the use of whereis command in linux?
        Whereis command is used to find the binaries and libraries files of an application in linux.

   218. What is the use of man pages?
        Man pages stand for manual pages. It is the documentation about and helps you to understand the commands 
        and how to use the commands. Eg: man wget.

   219. what does “2>” indicate in redirection?
        This means that output will be shown on the screen and the errors will be written to a file that you specify.
        Eg: # ls /etc/test 2> error.txt

   220. What are the different type of users that you have in Linux?
        You have 2 types of users in linux. They are
         • root user
         • standard users.

   221. How To check Memory stats and CPU stats ?
        free & vmstat commands.

   222. What is the purpose of runlevels ?
        Useful for debugging purpose. Basic idea is each runlevel has some services operational and depending
        on need can enable different runlevels to test which services are running

   223. You are able to ping with a numeric IP address, but not by name. How will you debug ?
        First check /etc/resolv.conf file for DNS Server Entry

   224. Generally setting up services in Linux require ————— and ————–
        Update the associated configuration file and ensure the appropriate daemon is started

   225. What is the purpose of iptables command ?
        Basically allows rule creation to filter packets according to established criteria. Network Address
        Translation function is also done

   226. You are noticing mails are not sent by sendmail. Where can you find the error log to see what happened ?

   227. How can you findout the current runlevel the system is in ?
          # who -r

   228. Linux system has crashed and keeps getting to Debug Prompt. How do you bring it to normal login prompt.
         Likely due to file system inconsistency, run fsck to check and accept inode repairs.

   229. How can you customise startup settings for your login in bash shell
        You can use file .bashrc for this customisation.

   230. What is the first process started by the Schedulerin RHEL 6.

   231. How can you find the current status of Virtual memory in the Linux System ?
        # cat /proc/meminfo * Note the very useful /proc filesystem

   232. Hardware devices are identified as special files in Linux. Name the types.
        Character,block and Network

   233. Name 3 Environment variables

   234. Where is my vmlinuz executable loaded from ?

   235. As System Administrator you have to apply a patch that is in .tar.gz format. How would you use it ?
        Get the file and apply tar -zxvf <filename.tar.gz>

   236. What are Kernel types and which one is Linux ?
        Monolithic and Micro. Linux is a Monolithic Kernel.

   237. As System Admin, log files are monitored as they grow. How is this achieved ?
        tail -f

   238. Automatic mounting of new file system at boot-time can be done by
        Adding an entry in /etc/fstab file

   239. You recently ran an install, the command for which you need to recall. How do you get this?
         # history

   240. In writing a Bash Shell script, special character’ meaning has to be altered. How is it done?
        Escape sequence. Precede the special character with a ‘\’

   241. Linux associates devices with File Descriptors. List them.
        0 – Standard Input
        1- Standard Output
        2-Standard Error

   242. How do you set a mask to stop certain permissions from being granted by default on file creation?
          # umask <value>

   243. You want to try out a Distribution before installation. Which image would suit?

   244. System Administrators monitor load averages on System for analysis. How is this done?
        # top
        # uptime
        # w

   245. What is the behaviour of the following very useful grep command ?
         # grep [abc] file1 : Looks for matches in file1 containing either an a or b or c character.

   246. You need to make a file with only read permissions for yourself, group and all. How can you ?
         #chmod 444 file1

   247. What does su – do ? Give an example of when you would use this.
        Gets the switch to root account. Need to be done before Software installation.

   248. Pipe is a very important concept in process communication. Give an example
         # cat file1 |grep xyz : Pattern matching by grep happens on the displayed file1

   249. In Shell scripting command return codes are checked prior to proceeding. Explain
        These are Exit status codes. Linux follows 0 for success and nonzero codes for failures

   250. Signals is one way that process communication happens in Linux. What does ctrl C do ?
        Generates a SIGINT signal that stops the current process running in the shell.

   251. To set a password to the boot loader:
         # grub
           grub> md5crypt
           Password: ************
           Encrypted: $1$3yQFp$MEDEglsxOvuTWzWaztRly.
           grub> quit

           Next, add this to your grub.conf file like so:
           password –md5 $1$3yQFp$MEDEglsxOvuTWzWaztRly.

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