Commonly ask Linux Interview Questions

You need to see the last fifteen lines of the files dog, cat and horse. What command should you use?

tail -15 dog cat horse 

The tail utility displays the end of a file. The -15 tells tail to display the last fifteen lines of each specified file. 

Who owns the data dictionary? 

The SYS user owns the data dictionary. The SYS and SYSTEM users are created when the database is created. 

You routinely compress old log files. You now need to examine a log from two months ago. Which utility is using in order to view its contents without first having to decompress it?

zcat 

The zcat utility allows you to examine the contents of a compressed file much the same way that cat displays a file. 

You suspect that you have two commands with the same name as the command is not producing the expected results. What command can you use to determine the location of the command being run? 

which 

The which command searches your path until it finds a command that matches the command you are looking for and displays its full path. 

You locate a command in the /bin directory but do not know what it does. What command can you use to determine its purpose?

whatis 

The whatis command displays a summary line from the man page for the specified command. 

You wish to create a link to the /data directory in bob's home directory so you issue the command ln /data/home/bob/datalink but the command fails. What option should you use in this command line to be successful?

Use the -F option 

In order to create a link to a directory you must use the -F option. 

When you issue the command ls -l, what the first character of the resulting display represents the file?

 

type 

The first character of the permission block designates the type of file that is being displayed. 

What utility can you use to show a dynamic listing of running processes? 

top 

The top utility shows a listing of all running processes that is dynamically updated.

Where standard output is usually directed? 

to the screen or display 

By default, your shell directs standard output to your screen or display. 

You wish to restore the file memo.ben which was backed up in the tarfile MyBackup.tar. What command should you type?

tar xf MyBackup.tar memo.ben 

This command uses the x switch to extract a file. Here the file memo.ben will be restored from the tarfile MyBackup.tar. 

You need to view the contents of the tarfile called MyBackup.tar. What command would you use?

tar tf MyBackup.tar 

The t switch tells tar to display the contents and the f modifier specifies which file to examine. 

You want to create a compressed backup of the users' home directories. What utility should you use? 

tar 

You can use the z modifier with tar to compress your archive at the same time as creating it. 

What daemon is responsible for tracking events on your system? 

syslogd 

The syslogd daemon is responsible for tracking system information and saving it to specified log files. 

You have a file called phonenos that is almost 4,000 lines long. What text filter can you use to split it into four pieces each 1,000 lines long? 

split 

The split text filter will divide files into equally sized pieces. The default length of each piece is 1,000 lines. 

You would like to temporarily change your command line editor to be vi. What command should you type to change it? 

set -o vi 

The set command is used to assign environment variables. In this case, you are instructing your shell to assign vi as your command line editor. However, once you log off and log back in you will return to the previously

defined command line editor. 

What account is created when you install Linux? 

root 

Whenever you install Linux, only one user account is created. This is the superuser account also known as root. 

What command should you use to check the number of files and disk space used and each user's defined quotas? 

repquota 

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.

In order to run fsck on the root partition, the root partition must be mounted as? 

readonly 

You cannot run fsck on a partition that is mounted as read-write.

In order to improve your system's security you decide to implement shadow passwords. What command should you use? 

pwconv 

The pwconv command creates the file /etc/shadow and changes all passwords to 'x' in the /etc/passwd file.

Bob Armstrong, who has a username of boba, calls to tell you he forgot his password.What command should you use to reset his command? 

passwd boba 

The passwd command is used to change your password. If you do not specify a username, your password will be changed. 

The top utility can be used to change the priority of a running process? Which another utility that can also be used to change priority?

nice 

Both the top and nice utilities provide the capability to change the priority of a running process. 

What command should you type to see all the files with an extension of 'mem' listed in reverse alphabetical order in the /home/ben/memos directory?

ls -r /home/ben/memos/*.mem 

The -c option used with ls results in the files being listed in chronological order. You can use wildcards with the ls command to specify a pattern of filenames. 

What file defines the levels of messages written to system log files? 

kernel.h 

To determine the various levels of messages that are defined on your system, examine the kernel.h file. 

What command is used to remove the password assigned to a group? 

gpasswd -r 

The gpasswd command is used to change the password assigned to a group. Use the -r option to remove the password from the group. 

What command would you type to use the cpio to create a backup called backup.cpio of all the users' home directories? 

find /home | cpio -o > backup.cpio 

The find command is used to create a list of the files and directories contained in home. This list is then piped to the cpio utility as a list of files to include and the output is saved to a file called backup.cpio. 

What can you type at a command line to determine which shell you are using? 

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. 

What type of local file server can you use to provide the distribution installation materials to the new machine during a network installation?

A) Inetd

B) FSSTND

C) DNS

D) NNTP

E) NFS 

E - You can use an NFS server to provide the distribution installation materials to the machine on which you are performing the installation.

If you type the command cat dog & > cat what would you see on your display?  

a. Any error messages only.

b. The contents of the file dog.

c. The contents of the file dog and any error messages.

d. Nothing as all output is saved to the file cat. 

d 

When you use & > for redirection, it redirects both the standard output and standard error. The output would be

saved to the file cat.

You are covering for another system administrator and one of the users asks you to restore a file for him. You locate the correct tarfile by checking the backup log but do not know how the directory structure was stored. What command can you use to determine this? 

a. tar fx tarfile dirname

b. tar tvf tarfile filename

c. tar ctf tarfile

d. tar tvf tarfile 

d 

The t switch will list the files contained in the tarfile. Using the v modifier will display the stored directory structure. 

You have the /var directory on its own partition. You have run out of space. What should you do? 

a. Reconfigure your system to not write to the log files.

b. Use fips to enlarge the partition.

c. Delete all the log files.

d. Delete the partition and recreate it with a larger size. 

d 

The only way to enlarge a partition is to delete it and recreate it. You will then have to restore the necessary files from backup. 

You have a new application on a CD-ROM that you wish to install. What should your first step be?

a. Read the installation instructions on the CD-ROM.

b. Use the mount command to mount your CD-ROM as read-write.

c. Use the umount command to access your CD-ROM.

d. Use the mount command to mount your CD-ROM as read-only. 

d 

Before you can read any of the files contained on the CD-ROM, you must first mount the CD-ROM. 

When you create a new partition, you need to designate its size by defining the starting and ending _____________. 

cylinders 

When creating a new partition you must first specify its starting cylinder. You can then either specify its size or the ending cylinder.

What key combination can you press to suspend a running job and place it in the background?

ctrl-z 

Using ctrl-z will suspend a job and put it in the background.

The easiest, most basic form of backing up a file is to _____ it to another location. 

copy 

The easiest most basic form of backing up a file is to make a copy of that file to another location such as a floppy disk. 

What type of server is used to remotely assign IP addresses to machines during the installation process? 

A) SMB

B) NFS

C) DHCP

D) FT

E) HTTP

C - You can use a DHCP server to assign IP addresses to individual machines during the installation process.

Which password package should you install to ensure that the central password file couldn't be stolen easily? 

A) PAM

B) tcp_wrappers

C) shadow

D) securepass

E) ssh

C - The shadow password package moves the central password file to a more secure location.

When using useradd to create a new user account, which of the following tasks is not done automatically. 

a. Assign a UID.

b. Assign a default shell.

c. Create the user's home directory.

d. Define the user's home directory.

c 

The useradd command will use the system default for the user's home directory. The home directory is not created, however, unless you use the -m option.

You want to enter a series of commands from the command-line. What would be the quickest way to do this?

a. Press enter after entering each command and its arguments

b. Put them in a script and execute the script

c. Separate each command with a semi-colon (;) and press enter after the last command

d. Separate each command with a / and press enter after the last command

c 

The semi-colon may be used to tell the shell that you are entering multiple commands that should be executed serially. If these were commands that you would frequently want to run, then a script might be more efficient. However, to run these commands only once, enter the commands directly at the command line. 

You attempt to use shadow passwords but are unsuccessful. What characteristic of the /etc/passwd file may cause this?  

a. The login command is missing.

b. The username is too long.

c. The password field is blank.

d. The password field is prefaced by an asterisk. 

c 

The password field must not be blank before converting to shadow passwords. 

When you install a new application, documentation on that application is also usually installed. Where would you look for the documentation after installing an application called MyApp?

a. /usr/MyApp

b. /lib/doc/MyApp

c. /usr/doc/MyApp

d. In the same directory where the application is installed.

c 

The default location for application documentation is in a directory named for the application in the /usr/doc directory. 

What file would you edit in your home directory to change which window manager you want to use? 

A) Xinit

B) .xinitrc

C) XF86Setup

D) xstart

E) xf86init

Answer: B - The ~/.xinitrc file allows you to set which window man-ager you want to use when logging in to X from that account. 

What command allows you to set a processor-intensive job to use less CPU time? 

A) ps

B) nice

C) chps

D) less

E) more

Answer: B - The nice command is used to change a job's priority level, so that it runs slower or faster.

While logged on as a regular user, your boss calls up and wants you to create a new user account immediately. How can you do this without first having to close your work, log off and logon as root?  

a. Issue the command rootlog.

b. Issue the command su and type exit when finished.

c. Issue the command su and type logoff when finished.

d. Issue the command logon root and type exit when finished. 

Answer: b 

You can use the su command to imitate any user including root. You will be prompted for the password for the root account. Once you have provided it you are logged in as root and can do any administrative duties.

There are seven fields in the /etc/passwd file. Which of the following lists all the fields in the correct order?  

a. username, UID, GID, home directory, command, comment

b. username, UID, GID, comment, home directory, command

c. UID, username, GID, home directory, comment, command

d. username, UID, group name, GID, home directory, comment

Answer: b 

The seven fields required for each line in the /etc/passwd file are username, UID, GID, comment, home directory, command. Each of these fields must be separated by a colon even if they are empty. 

Which of the following commands will show a list of the files in your home directory including hidden files and the contents of all subdirectories?

a. ls -c home

b. ls -aR /home/username

c. ls -aF /home/username

d. ls -l /home/username

Answer: b 

The ls command is used to display a listing of files. The -a option will cause hidden files to be displayed as well. The -R option causes ls to recurse down the directory tree. All of this starts at your home directory. 

In order to prevent a user from logging in, you can add a(n) ________at the beginning of the password field.

Answer: asterick 

If you add an asterick at the beginning of the password field in the /etc/passwd file, that user will not be able to log in. 

You have a directory called /home/ben/memos and want to move it to /home/bob/memos so you issue the command mv /home/ben/memos /home/bob. What is the results of this action?

a. The files contained in /home/ben/memos are moved to the directory /home/bob/memos/memos.

b. The files contained in /home/ben/memos are moved to the directory /home/bob/memos.

c. The files contained in /home/ben/memos are moved to the directory /home/bob/.

d. The command fails since a directory called memos already exists in the target directory. 

Answer: a 

When using the mv command to move a directory, if a directory of the same name exists then a subdirectory iscreated for the files to be moved.

Which of the following tasks is not necessary when creating a new user by editing the /etc/passwd file? 

a. Create a link from the user's home directory to the shell the user will use.

b. Create the user's home directory

c. Use the passwd command to assign a password to the account.

d. Add the user to the specified group.

Answer: a 

There is no need to link the user's home directory to the shell command. Rather, the specified shell must be present on your system. 

You issue the following command useradd -m bobm But the user cannot logon. What is the problem? 

a. You need to assign a password to bobm's account using the passwd command.

b. You need to create bobm's home directory and set the appropriate permissions.

c. You need to edit the /etc/passwd file and assign a shell for bobm's account.

d. The username must be at least five characters long.

Answer: a 

The useradd command does not assign a password to newly created accounts. You will still need to use the passwd command to assign a password.

You wish to print the file vacations with 60 lines to a page. Which of the following commands will accomplish this?

a. pr -l60 vacations | lpr

b. pr -f vacations | lpr

c. pr -m vacations | lpr

d. pr -l vacations | lpr

Answer: a 

The default page length when using pr is 66 lines. The -l option is used to specify a different length. 

Which file defines all users on your system?

a. /etc/passwd

b. /etc/users

c. /etc/password

d. /etc/user.conf

Answer: a 

The /etc/passwd file contains all the information on users who may log into your system. If a user account is not contained in this file, then the user cannot log in. 

Which two commands can you use to delete directories? 

A) rm

B) rm -rf

C) rmdir

D) rd

E) rd -rf

Answer(s): B, C - 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. 

Which partitioning tool is available in all distributions? 

A) Disk Druid

B) fdisk

C) Partition Magic

D) FAT32

E) System Commander

Answer(s): B - The fdisk partitioning tool is available in all Linux distributions.

What command can you use to review boot messages? 

Answer: dmesg 

The dmesg command displays the system messages contained in the kernel ring buffer. By using this command immediately after booting your computer, you will see the boot messages. 

What is the minimum number of partitions you need to install Linux? 

Answer: 2 

Linux can be installed on two partitions, one as / which will contain all files and a swap partition.