Top 40 Linux commands every sysadmin should know

by Jay

Top 40 Linux commands every sysadmin should know

To get login user information, including the number of currently logged-in users and their processes:

# w

To see the list of users who are currently logged in and on which terminal they are logged in:

# who

To view the list of users who have logged in and out since the /var/log/wtmp file was created:

# last

To see the list of users who have attempted bad logins:

# lastb

To see the list of all reboots since the log file was created:

# last reboot

To see information about system uptime, including the time the system has been running, the number of logged-in users, and the load average:

# uptime

Note: The load average is displayed for 1 sec, 5 secs, and 15 secs intervals.

To view the mounted partitions, their mount points, and amount of disk space used:

# df

To see the disk usage of each file in bytes:

# du

To get the current kernel version:

# uname -r

To view the last shutdown date and time:

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# last -x

To display only the shutdown time using grep:

# last -x | grep shutdown

Note: grep is used to search for a word or sentence in a file, and find is used to search for a command or file inside the system.

To view the list of shells supported by Linux:

# cat /etc/shells

or

# chsh -l

Default shells:

/bin/sh ------> default shell for Unix
/bin/bash ------> default shell for Linux
/sbin/nologin ------> users cannot login shell
/bin/tcsh ------> c shell to write 'C++' language programs
/bin/csh ------> c shell to write 'C' language programs

To see the current shell:

# echo $SHELL

To change the shell for a specific user:

# chsh <user name>

To display the time only:

# date + %R

To display the date only:

# date + %x

To see the history of commands:

# history

To clear the history of commands:

# history -c

To recover the history of commands:

# history -r

To check the current history size:

# echo $HISTSIZE

To change the current history size to 500 temporarily:

# export HISTSIZE=500

To display the date and time of each command temporarily:

# export HISTTIMEFORMAT=" "%D" "%T" "

To make history size and date & time formats permanent:

Open this file, go to the last line, and add the following lines

# vim /etc/bashrc

HISTSIZE=1000
HISTTIMEFORMAT=' %D %T '

(Save and exit the file, and update the effects by using the command:)

# source /etc/bashrc

To go to the user’s home directory:

# cd ~ <user name>

To see the short description of a command:

# whatis <command>

To see the location of a command and its documentation:

# whereis <command>

To refresh the terminal:

# reset

To see the current user name:

# whoami

To see the current user with full details like login time and others:

# whoami

To change the password of a user:

# passwd <user name>

To see the current user name, user ID, group name, and group ID:

# id

To see the specified user name, user ID, group name, and group ID:

# id <user name>

To switch to the root user without root user home directory:

# su

To switch to the root user with root user home directory:

# su -

To switch to a specified user without his home directory:

# su <user name>

To switch to a specified user with his home directory:

# su - <user name>

To list all the PCI slots present in the system:

# lspci

To see the size of /etc on the disk in KBs or MBs:

# du -sh /etc/

For more Linux commands Visit this Link All Linux Commands Help

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