Linux Interview Questions with Answers

Certiology’s Free Linux interview questions with answers are exactly what you need to prepare for linux administrator interview.

1. What is the full form of GNU?
Ans: GNU is NOT UNIX (It’s also known as a recursive acronym)

2. In Linux what is the usual size we use for swap partition?
Ans: Recommended size is twice the amount of physical memory but if shortage of memory, then at least the same size of memory.

3. Which command is used to change permissions on Linux?
Ans: Chmod

4. The system configuration in Linux is stored under which path?
Ans: /etc

5. The command used to change password is _________________
Ans: Passwd

6. Which Linux Service or server configuration is used for Linux and Windows to communicate or share files?
Ans : Samba is used for SMB and CIFS systems.

7. Which command is used to customize a command? Eg. To use ‘cls’ instead of ‘clear’
Ans: You need to make the modification in /etc/bashrc and use the alias command.

8. Why you should prefer using ssh over Telnet to connect to a Linux system remotely?
Ans: In Telnet data is sent as plain text thus the password can be easily snipped over the network so its recommended to use ssh.

9. _______________ Utility is used for repairing a corrupted file system.
Ans: fsck

10. During the Linux boot up, some messages are seen which show the services started as OK or FAILED. How can you see the messages that were already scrolled up.
Ans: These messages are known as kernel boot messages and stored in /var/log/dmesg

11. General system log messages are stored in which path?
Ans: /var/log/messages

12. What is full form of SMTP and why is it used ?
Ans: SMTP stands for Simple Mail Transfer Protocol and is used for sending emails.

13. _____________ is a service of Sendmail used for transferring mail from one network to other or one host to other.
Ans: MTA (Mail Transfer Agent)

14. Which is the command used to monitor system activities?
Ans: top

15. ____________ Command is used to change permissions of folders and files.
Ans: chmod

16. Which ports should be open on a firewall for an email server?
Ans: Port 110, 143 and 25

17. Which ports should be open on a firewall for an Web server?
Ans: Port 80 and 443

18. TFTP uses which port number ________
Ans: 69

19. _________ And __________ are used in Linux as scheduler ( talk or job scheduler).
Ans: at and cron

20. To find users show have logged into a Linux system and their login attempts _________ or ________ command is used.
Ans: ‘w’ or ‘who’

21. ____ command is used to rename files in Linux
Ans: mv

22. Protocol number for TCP is ______ and for UDP is __________
Ans: TCP: 6 and UDP 17

23. SNMP works on which port number?
Ans: 161 and SNMP traps 162

24. _________ Command in Linux is used to check the configured IP address and other IP information like gateway, subnet mask etc.
Ans: ifconfig

25. A harddisk speed is measured in RPM, what does it stand for ______________
Ans: Revolutions per minutes

26. To configure your linux machine as a router what command can be used?
Ans: we can use the ip_forward option with setting it to 1. (Echo 1 > /proc/sys/net/ipv4/ip_forward)

27. What is the UID and GID of a root user?
Ans Zero (0), bith UID and GUID are zero.

28. You use the mount command to mount a drive / path, how to you make it persistent to reboots.
Ans: by making an entry for the path in the /etc/fstab path.

29. ________ command is used to make partitions
Ans: fdisk

30. _________ command updates the partition table
Ans: part probe

31. Can data be written to a disk after partitioning and not formatting it?
Ans: No data cannot be written until it is formatted with a file system

32. _______ Command is used to check size or free space or consumed space on the Linux box.
Ans : df –h

33. RPM in Linux packages stands for ____________________
Ans: Redhat pluggable modules

34. ______ cpmmand is used to check if a package is installed on the Linux box
Ans : rpm –qa ( query all)
For selective: rpm –qa | grep samba -> return only samba related output

35. Which command helps see RAM details?
Ans: free

36. Which command is used to remove swap?
Ans: swapoff

37. MBR stands for _____________
Ans: Master Boot Record

38. What is the MBR size : ___________
Ans: 152 bytes

39. What is full form of LILO :___________
Ans: Linux Loader

40. _______________ is a chain of processes where output of one process is used as input for other
Ans: Pipe

41. _____ command is used to find DNS related info in Linux.
Ans: dig and nslookup

42. To check the connectivity of two devices ro the network, ________ command is used.
Ans: ping

43. The username and password is stored in which file _____________
Ans: /etc/passwd

44. _________ command is used to change priority of jobs.
Ans: nice command

45. To add a new user name harry what is the command used?
Ans: useradd harry

46. MySql database dump is taken using ______ command
Ans: Mysqldump databasename > dumpname

47. What is the full form of AIX in terms of IBM AIX servers?
Ans: Advance Inetractive Executive

48. Unix was invented by ______________ and __________________
Ans: Denis Ritche and Ken Thompson

49. ________________ command is used to add groups
Ans: groupadd

50. _______ Folder contain base executables that are necessary for minimal function of the system.
Ans: /bin

51. __________ Command is used to delete files.
Ans: rm

52. _________ command is used to remove a directory
Ans: rmdir

53. To make logs gets rotated automatically which command is used ____________
Ans: logrotate

54. _________ command is used to make a file system in Linux
Ans: mkfs (Make File System)

55. Full form of BASH is _________
Ans: Boyrne Again Shell

56. A file transfer protocol that is connectionless protocol is ______________
Ans: TFTP

57. What is LVM and why is it required?
Ans: It means Logical Volume Manager and is used for resizing of file systems.

58. Port number for Squid Proxy is ___________
Ans: 3128

59. ________ command is used to check the default route
Ans: netstat –rn

60. __________ can be used only for files and not for directories
Ans: hard link

61. How may run levels are available in Linux?
Ans: 7

62. What is run level 5?
Ans: Multi user mode with GUI

63. SeLinux means?
Ans: Security Enhanced Linux

64. GRUB stands for _______________
Ans: GRand Unified Boot Loader

65. The man command is used to see __________
Ans: the manual pages

66. RAID stands for _____________
Ans: Redudant Array of Inexpensive Disks

67. While using gdb for debugging a command BT is used, what does this mean?
Ans: BackTrace

68. To make a service start on startup what command is used?
Ans: chkconfig

69. In Linux you can create many partitions, what is the minimum number of partitions required and which are those ?
Ans: minimum 2 partitions namely, root (/) and swap.

70. UIDs from which number can be used for normal users and accounts.
Ans: From 100-999

71. To know the current dat what is the command used?
Ans: date

72. What is the main difference between TCP and UDP protocol?
Ans: TCP is connection oriented and UDP is connection less.

73. To run a job in background what operator is used?
Ans: Ampersand ( &) . eg. Cp source destination & (the copy will run in background)

74. _____ command is used to list files and directories.
Ans: ls –l

75. To create a 0kb file what command is used?
Ans: touch

76. What does r, w, and x means in reference to file names?
Ans: r : Read, w : write, x : execute

77. What is the value associate with rwx?
Ans: r:->4
w:->2
x:-> 1

78. Full form of FIFO is _______________
Ans: First In First Out

79. ___________ system call creates a new process
Ans: fork ()

80. ________ system call gets the parent process identifier
Ans: getppid

81. To see last 10 line of a file what command is used?

Ans: tail -10 ( eg. Tail -10 /var/log/svlog shows last 10 lines of this file)

82. The ___________ is used to dynamically assign IP address to a client
Ans: DHCP Server

83. What are the process states in Linux?
Ans: Running, Interruptible, uninterruptable, stopped and Zombie.

84. What is a Zombie process?
Ans: It is a process which is terminated but the table still has the process information

85. What is full form of YUM and why is it used?
Ans: YUM: Yellow dog Updater; it is used for installation of packages.

86. The _____________command is used to install packages using yum
Ans: yum install < package name>

87. To install a package using rpm what is the command used? Example install ftp
Ans: rpm –ivh < package name>

88. The ________________command is used to list ACLs for a file..
Ans: getfacl < filename>

89. Ext 3 is better than ext 2 because it supports a main point called_____________
Ans: Journaling

90. Can we convert ext2 to ext3? If so by which command?
Ans: yes we can use the command tune2fs

91. What does CUPS stand for in Linux / UNIX?
Ans: Common Unix Prining system

92. Which RAID is considered as Mirroring?
Ans: RAID 1

93. _____________server is used with BIND package
Ans: Named

94. __________command is used to create an archive of files and folders?
Ans: tar –cvfz

95. The TCP 3 way handshake consists of which steps:
Ans: SYN, SYN + ACK and ACK

96. _________________ is a very popular version control system
Ans: GIT

97. How do you bring down eth0
Ans: ifcfg ethdown

98. Full form of Ping is _______________________
Packet Internet Groper

99. ______________________ Command help troubleshoot by showing how many hops it took to reach a destination.
Ans :-> traceroute < destination>

100. DIG command is used to query DNS related information. DIG stands for :
Ans: Domain Internet Groper

101. As per the company policy you want the user ‘munjal’ to change the password at next logon, how do you force him to do that.
Ans: chage –d 0 “munjal”