Linux Commands & Options Cheat Sheet

*Shortcut*	*What It Does*	*Notes*
Esc + .	Insert last argument entered	Repeat to go back to previous arguments
Up Arrow	Auto-fill last command entered	Repeat to go back to previous commands
Ctrl+D	Logout / Exit
Ctrl+L	Clear terminal output
Ctrl+Shift+T	Open new terminal tab
Ctrl+Arrow (Right/Left)	Move to beginning/end of a word

*Wildcard*	*What It Represents*	*Example*
`~`	Current user's home directory
`.`	The directory you're currently in
`..`	Parent directory of your current directory
`*`	All files in current directory	`ls i*` = all files starting with "i"
`?`	"Any character"	`f??e` matches anything with 4 characters that starts with "f" & ends with "e"
`[aou]`	Match to any one of the enclosed characters	`c[aou]t` matches to "cat", "cot", and "cut"
`!!`	"Last command run" (inserts into current command)	`sudo !!` = rerun command as root
`^x^y`	Rerun last command but replace x with y	`ls /usr` followed by `^usr^tmp` will run `ls /tmp`
`!3`	Rerun 3rd command from command history
`!ls`	Runs most recent command from history that had "ls" in it

*Directory/File*	*(Stands For) Purpose*
/root	Root user's home directory
/home	Normal users' home directories
/var	(Variables) Database locations, spool files for mail, etc.

/usr	(User System Resources) System resources used by users
— /usr/bin	(Binaries) Executables usable by normal users
— /usr/sbin	(System Binaries) Executables only usable by root user
— /usr/lib	52-bit libraries
— /usr/lib64	64-bit libraries

/etc	(Extended Text Configurations) Configuration files
— /etc/passwd	User account config files
— /etc/group	Group membership info & config files
— /etc/shadow	User password info & config files
— /etc/sudoers	Main file for sudo config
— /etc/sudoers.d/	Destination for sudo config "dropping files"
— /etc/login.defs	Defines default properties used for new user accounts

--- Command Mode ---
o	Starts new line and switches to Insert mode
cw	"Change word" - deletes word and switches to Insert mode
G	Go to end of file
dd	Delete or cut entire line
yy	Copy entire line
p	Paste copied text
x	Delete character cursor is on top of
dw	Delete word cursor is on top of
d$	Delete from cursor to end of line
ZZ	Save & quit (existing files)
--- Extended Command Mode ---
:w filename	Save (new files)
:wq	Save & quit (existing files)

`echo`
`date`
		`+%F`
		`+%R`
		`+%s`
`tmux`
`ps -au`	Show current processes & which user started them
`ssh user@ip.address`
		`-v`	verbose; shows in detail what's happening while establishing connection
		`-Y`	enables graphical application support
		`-p port#`	connect to ssh service not listening on default port 22

`ls dir1`	List contents of dir1
	`-l`	additional info (owner, perms, etc.)
	`-a`	lists all, including hidden files
	`-i`	adds file inode to info displayed
	`-d`	info for directory itself (rather than its contents)
`mkdir dir1`	Create a new directory
	`-p`	creates full path (multiple directories if needed)
	`-v`	verbose (output shows action taken)
`cp dir1 dir2`		Copy dir1 into dir2
	`-r`	recursively ("and its contents")

`rm dir1`	Removes (deletes) an empty directory
	`-r`	recursively ("and it's contents"), including special files

`mv file1 dir1`	Move file1 into dir1
	`-v`	verbose (output shows action taken)

`ln target link`	Creates a hard link from file "link" to file "target"
	`-s`	makes a symbolic link instead of a hard link

*Command*	*Options*	*What It Does*
`id user1`	Show UID, GID, & secondary groups (current user if not specified)
`getent passwd usr1`	Find out if usr1 is known to the system
`useradd user1`	Add a new user
`useradd user1`	`-u #`	set a specific UID
	`-s /sbin/nologin`	create a user without a login shell
`usermod user1`	Change properties of existing user
	`-c "text"`	adds text to comment field
	`-g group1`	changes primary group to group1
	`-G group1`	replaces supplementary group with group1
	`-aG group1`	appends group1 to supplementary groups
	`-L user1`	locks user1's account (instead of deleting)
`newgrp group1`	Change current user's primary group (temporary; current session only)
`userdel user1`	Deletes user1 but not their home directory
`userdel user1`	`-r`	deletes both user and home directory
`groups user1`	Displays simple list of groups user1 is a member of
`passwd user1`	Set password for user1
`chage user1`	Change password aging properties for user
	`-m days`	minimum # of days between password changes
	`-M days`	maximum # of days between password changes
	`-W days`	warning period before password expires
	`-I days`	inactivity period (password usable after expiration)
	`-d 0`	require password change on next login
	`-E date`	date when account expires
`getent group grp1`	Find out if grp1 is known to the system
`groupadd group1`	Create a new group
	`-g #`	set a specific GID
	`-r`	create a system group
`groupmod group1`	Change properties of existing group
`groupmod group1`	`-g #`	change GID to specified number

To set the number of days from today when user's account expires:

chage -E $(date +days %Y-%m-%d)

To give full admin privileges to a user or group:

echo "[user1|%group1] ALL=(ALL) ALL" >> /etc/sudoers.d/name

Linux Commands & Options Cheat Sheet (DRAFT) by Tamaranth