Basic Commands

cp

-a, --archive Combines the d, p and r options
-b, --backup before removal, make a backup
-d, --no-deference preserve links
-f, --force remove existing destinations without prompting
-i, --interactive show prompt before overwriting
-l, --link link files instead
-p, --preserve preserve file attributes
-r, --recursive recursively copy directories

column

Arrange output in columns
-t create table

hostname

Shows the current hostname.
-f show FQDN

hostnamectl status (default) show current system hostname and related information.
hostnamectl set-hostname set and apply a new hostname

last

Show a list of last logged in users and system boots.
Can be refined with a username/keyword.

lastb

Show a list of last failed login attempts.
Can be refined with a username/keyword.

ls

List files and folders.
-a do not ignore entries starting with .
-F append a symbol to indicate type (* executable, / directory, @ symlink, = socket, | named pipe, > door)
-h (with -l and -s) print sizes like 1K 234M 5G
-i display inode number
-l use a long listing format
-r reverse order while sorting
-s display size
-t sort by time, newest first

less & more

space / f scroll forward one screen
enter scroll forward one line
b scroll backward one screen
d scroll forward half a screen
h display help
q quit
/string search string forward
?string search string backward
n find next occurrence
N find previous occurrence (less only)

setfacl

-b remove all access acls
-d apply default acl
-k remove all default acls
-m set or modify acls
-n prevent automatic recalculation of mask
-R apply recursive
-x remove access acl

sort

Used to sort output.
-u only display unique names
-n numeric sort
-r reverse order

w

Display current system information.

watch

Execute a command every X seconds (default 2).
watch -n X who execute the who command every X seconds

wc

Display lines (-l), words (-w), bytes (-c) or characters (-m) of file.

whatis

Display one-line man page description of a command.

whereis

Locate the binary, source and man pages for a command.

which

Locate a command.

who

Display currently logged in users.