Linux Commands

List files and Navigate

Command	Description
`ls`	list files and directories in cwd
`ls-R`	also list files in sub directories
`ls-a`	also list hidden files
`ls-al`	list files with detailed info like permissions and size
`cd or cd~`	go home
`cd ..`	navigate up 1 level
`cd <dir>`	navigate to
`cd /`	navigate to root
`history`	list of all past commands typed in terminal
`clear`	clear terminal
`man`	help on command
`apt-get`	install/update (some) package
`chsh`	change shell
`printenv`	display all env variables (or `env`)
`printenv <KEY>`	display value of env variable
`export <KEY>`	set env variable (or `unset`)
`sudo`	elevated privileges (superuser/root)
`sudo ln -sf /bin/zsh bin/sh`	link shell to /bin/zsh (older)
`sudo ln -sf /bin/dash bin/sh`	link shell to /bin/dash (newer)

Command	Description
`cat filename`	display file contents
`cat < filename`	display file contents
`cat file1 file2`	display contents of multiple files
`cat file1; cat file2`	display contents of multiple files
`cat song.text more`	display more (or `less`) of file content
`cat -n filename`	display file with line numbers
`cat -e filename`	display $ at the end of each line
`cat -T filename`	display file with tabs replaced by `^I`
`cat > filename`	create new file
`cat file > file2`	overwrite file2 with output of file1
`cat file >> file2`	append to file2 output of file1
`cat file1 file2 > file3`	join file1 and file2 and store in file3
`cat file1 file2 file3 sort > file4`	save sorted content to file4
`mv file path/to/location`	move file to new location
`mf filename new_name`	rename file to `new_name`
`rm filename`	remove file
`mkdir dir_name`	create directory
`rmdir`	delete directory
`mv`	rename directory
`pr -x`	divide file into x columns
`pr -h`	assign header to file
`pr -n`	denote file with line numbers
`diff file1 file2`	get diff of two files

Command	Description
`ls-l`	show file type and access permission
`r`	read permission
`w`	write permission
`x`	execute permission
`-=`	no permission
`chown user`	change ownership of file/directory
`chown user:group filename`	change user and group for a file/directory
`chmod 777 <filename>`	set program rwx permissions (owner, group, other)
`chmod 4755 <filename>`	change program to setuid

Command	Description
`lp -nc, lpr c`	print c copies of file
`lp-d lp-P`	specifies name of the printer

Send mail

1	`mail -s 'subject' -c 'cc-address' -b 'bcc-address' 'to-address'`

Send mail with attachment

1	`mail -s "Subject" to-address < Filename`

Command	Description
`sudo adduser username`	add new user
`sudo passwd -l 'username'`	change pwd of user
`sudo userdel -r 'username'`	remove newly created user
`sudo usermod -a -G GROUPNAME`	add user to a group
`sudo deluser USER GROUPNAME`	remove user from a group
`finger`	show info of all users logged in
`finger username`	show info on a specific user
`su username`	substitute user
`/usr/bin/passwd`	change current user password
`cat /etc/shadow`	read user passwords
`cat /etc/passwd`	lists all users

Command	Description
`SSH username@ip-address or hostname`	Login to remote linux machine using SSH
`Ping hostname="" or=""`	ping or analyze connection
`dir`	display files in current directory of remote computer
`cd "dirname"`	change to "dirname" on remote computer
`put file`	upload file from local to remote computer
`get file`	download file from remote to local computer
`quit`	logout

Command	Description
`bg`	send a process to the background
`fg`	run stopped process in the foreground
`top`	details on active processes
`ps`	Give status of processes running for a user
`ps PID`	Gives status of specified process
`pidof`	Get process ID (PID) of a process
`kill PID`	kill specified process
`nice`	Start process with given priority
`renice`	Change priority of a currently running process
`df`	Gives (amount of?) free hard disk space on system
`free`	Gives (amount of?) free RAM on system

Command	Description
`i`	Insert at cursor (goes into insert mode)
`a`	Write after cursor (goes into insert mode)
`A`	Write at the end of line (goes into insert mode)
`ESC`	Terminate insert mode
`u`	Undo last change
`U`	Undo all changes to the entire line
`o`	Open a new line (goes into insert mode)
`dd`	Delete line
`3dd`	Delete 3 lines
`D`	Delete contents of line after the cursor
`C`	Delete contents of a line after the cursor and insert new text. Press ESC key to end insertion.
`dw`	Delete word
`4dw`	Delete 4 words
`cw`	Change word
`x`	Delete character at the cursor
`r`	Replace character
`R`	Overwrite characters from cursor onward
`s`	Substitute one character under cursor continue to insert
`S`	Substitute entire line and begin to insert at the beginning of the line
`~`	Change case of individual character