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su switch user

su - switch to root

passwd change user's password

login sign into a new system

logout log out of a system

logname retun users login name

useradd create a new user or update default new user information

userdel remove a user account

usermod modify a user account

groupadd create a new group account

groupdel enable a super user or root to remove a group

groupmod enable a super user or root to modify a group

who display who is on the system

whois internet user name directory service

hostid print the numeric identifier for the current hosthostname set or print the name of the currnet host system

finger list information about the user

exit exit shell

reboot reboot the system

shutdown shutdown the system

shutdown -r minutes shutdown the system after the specified number of minutes

poweroff/halt stop the computer

sleep wait for x seconds to sleep

date set/display date and time

settime change file access and modificaiton time

cal calendar

time used to time a simple command

clear clear screen

echo display message on screen

printf write formatted output

df display free disk spaceuname show system information

whereis locate a binary, source, and manual page files for a command

env display environment variables

set set the value of an environment variable

setenv set the value of an environment variable

ftp enable ftp access to another terminal

telnet open a login session on the specified host

ping send an echo request via TCP/IP to the specified host

netstat show network status

mount/umount mount or unmount file systems and remote resources

jobs list the jobs currently running in the background

fg continue a stopped job by running it in the foreground

bg continue a stopped job in the background

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stop cancel a process execution

ps report the process status

ps -ef display full information about each of the processes now running

kill cancel a job, a process

which locate a command

. current directory

.. father directory

~ home directory

$HOME home directory

pwd print working directory

ls display directory contents

ls -l display directory contents in details

cd/chdir change directorymkdir make directory

mv change directory or file's name from src to tar or move the src into th

rmdir remove an existing directory (directory must not be empty)

rm remove files

rm -r remove directories (even not be empty)

rm -rf remove all files and subdirectories (dangerous command)

cp copy file

cp -r copy directory

chmod change the permission of a file

chown change the owner of a file

diff display two files and print the lines that are different

cmp compare two files

grep search for file(s) with given string, find text within a file

find . -print | sort print the current directory's structure

sort sort files

cat view and/or modify a file

more display file contents to screen (1 page at a time)

less opposite of more

head display the first part of the filetail display the last part of the file

wc display a count of lines, words, and characters in a file

tar compress or expand files

tar -cvvf file.tar myfile.txt

tar -cvvf home.tar home/

achieve a tar file

tar -xvvf myfile.tar

tar -xvzf myfile.tar.gz -C destdir

extract the file from a tar file

gzip/gunzip/gzcat compress or expand files