Linux
chown
Change file owner (user ID) and/or group (group ID)
chgrp
Change group ownership
mkdir -p
Create intermediate directories as required
users
List current users: users lists the login names of the users currently on the system, in sorted order, space separated, on a single line.
nano
Nano's ANOther editor, an enhanced free Pico clone
ssh
OpenSSH SSH client (remote login program): ssh (SSH client) is a program for logging into a remote machine and for executing commands on a remote machine. It is intended to provide secure encrypted communications between two untrusted hosts over an inse-cure network. X11 connections, arbitrary TCP ports and UNIX-domain sockets can also be forwarded over the secure channel. ssh connects and logs into the specified destination, which may be specified as either [user@]hostname or a URI of the form ssh://[user@]hostname[:port]. The user must prove his/her identity to the remote machine using one of several methods (see below).
uname
Print operating system name: The uname utility writes symbols representing one or more system characteristics to the standard output.
cal
The cal utility displays a simple calendar in traditional format and ncal offers an alternative layout, more options and the date of Easter. The new format is a little cramped but it makes a year fit on a 25x80 termi- nal. If arguments are not specified, the current month is displayed.
free
The free() function deallocates the memory allocation pointed to by ptr. If ptr is a NULL pointer, no opera- tion is performed.
grep
The grep utility searches any given input files, selecting lines that match one or more patterns. By default, a pattern matches an input line if the regular expression (RE) in the pattern matches the input line without its trailing newline. An empty expression matches every line. Each input line that matches at least one of the patterns is written to the standard output.
pinq
The ping utility uses the ICMP protocol's mandatory ECHO_REQUEST datagram to elicit an ICMP ECHO_RESPONSE from a host or gateway. ECHO_REQUEST datagrams (``pings'') have an IP and ICMP header, followed by a ``struct timeval'' and then an arbitrary number of ``pad'' bytes used to fill out the packet.
script
The script utility makes a typescript of everything printed on your terminal. It is useful for students who need a hardcopy record of an interactive session as proof of an assignment, as the typescript file can be printed out later with lpr(1).
w
The w utility prints a summary of the current activity on the system, including what each user is doing. The first line displays the current time of day, how long the system has been running, the number of users logged into the system, and the load averages. The load average numbers give the number of jobs in the run queue averaged over 1, 5 and 15 minutes. The fields output are the user's login name, the name of the terminal the user is on, the host from which the user is logged in, the time the user logged on, the time since the user last typed anything, and the name and arguments of the current process.
who
The who utility displays a list of all users currently logged on, showing for each user the login name, tty name, the date and time of login, and hostname if not local.
vi
Vi IMproved, a programmer's text editor
ssh-keygen
authentication key generation, management and conversion: ssh-keygen generates, manages and converts authentication keys for ssh(1). ssh-keygen can create keys for use by SSH protocol version 2. The type of key to be generated is specified with the -t option. If invoked without any arguments, ssh-keygen will generate an RSA key. ssh-keygen is also used to generate groups for use in Diffie-Hellman group exchange (DH-GEX). See the MODULI GENERATION section for details. Finally, ssh-keygen can be used to generate and update Key Revocation Lists, and to test whether given keys have been revoked by one. See the KEY REVOCATION LISTS section for details. Normally each user wishing to use SSH with public key authentication runs this once to create the authentication key in ~/.ssh/id_dsa, ~/.ssh/id_ecdsa, ~/.ssh/id_ed25519 or ~/.ssh/id_rsa. Additionally, the system administrator may use this to generate host keys, as seen in /etc/rc.
cd
change directory
chmod
change file modes or Access Control Lists
clear
clear the terminal screen
cat
concatenate and print files
cp
copy a file or directory
cut
cut out selected portions of each line of a file: The cut utility cuts out selected portions of each line (as specified by list) from each file and writes them to the standard output. If no file arguments are specified, or a file argument is a single dash (`-'), cut reads from the standard input. The items specified by list can be in terms of column position or in terms of fields delimited by a special character. Column numbering starts from 1.
file
determine file type:
du
display disk usage statistics: The du utility displays the file system block usage for each file argument and for each directory in the file hierarchy rooted in each directory argument. If no file is specified, the block usage of the hierarchy rooted in the current directory is displayed.
whoami
display effective user id: The whoami utility has been obsoleted by the id(1) utility, and is equivalent to ``id -un''. The command ``id -p'' is suggested for normal interactive use. The whoami utility displays your effective user ID as a name.
head
display first lines of a file
df
display free disk space: The df utility displays statistics about the amount of free disk space on the specified filesystem or on the filesystem of which file is a part. Values are displayed in 512-byte per block counts. If neither a file or a filesystem operand is specified, statistics for all mounted filesystems are displayed (subject to the -t option below).
date
display or set date and time: When invoked without arguments, the date utility displays the current date and time. Otherwise, depending on the options specified, date will set the date and time or print it in a user-defined way. The date utility displays the date and time read from the kernel clock. When used to set the date and time, both the kernel clock and the hardware clock are updated. Only the superuser may set the date, and if the system securelevel (see securelevel(7)) is greater than 1, the time may not be changed by more than 1 second.
top
display sorted information about processes: The top program periodically displays a sorted list of system processes. The default sorting key is pid, but other keys can be used instead. Various output options are available.
tail
display the last part of a file
rsync
faster, flexible replacement for rcp: rsync is a program that behaves in much the same way that rcp does, but has many more options and uses the rsync remote-update protocol to greatly speed up file transfers when the destination file is being updated. The rsync remote-update protocol allows rsync to transfer just the differences between two sets of files across the network connection, using an efficient checksum-search algorithm described in the technical report that accompanies this package.
last
indicate last logins of users and ttys: Last will list the sessions of specified users, ttys, and hosts, in reverse time order. Each line of output contains the user name, the tty from which the session was conducted, any hostname, the start and stop times for the session, and the duration of the session. If the session is still continuing or was cut short by a crash or shutdown, last will so indicate.
ln
link, ln -- make links: The ln utility creates a new directory entry (linked file) which has the same modes as the original file. It is useful for maintaining multiple copies of a file in many places at once without using up storage for the``copies''; instead, a link ``points'' to the original copy. There are two types of links; hard links and symbolic links. How a link ``points'' to a file is one of the differences between a hard and symbolic link.
ls
list directory contents
unzip
list, test and extract compressed files in a ZIP archive: unzip will list, test, or extract files from a ZIP archive, commonly found on MS-DOS systems. The default behavior (with no options) is to extract into the current directory (and subdirectories below it) all files from the specified ZIP archive. A companion program, zip(1L), creates ZIP archives; both programs are com- patible with archives created by PKWARE's PKZIP and PKUNZIP for MS-DOS, but in many cases the program options or default behaviors differ.
ls -l
lists all contents in long format
whereis
locate programs: The whereis utility checks the standard binary directories for the specified programs, printing out the paths of any it finds. The path searched is the string returned by the sysctl(8) utility for the ``user.cs_path'' string.
crontab
maintain crontab files for individual users (V3): The crontab utility is the program used to install, deinstall or list the tables used to drive the cron(8) daemon in Vixie Cron. Each user can have their own crontab, and they are not intended to be edited directly.
mkdir
make directory
tar
manipulate tape archives: tar creates and manipulates streaming archive files. This implementation can extract from tar, pax, cpio, zip, jar, ar, xar, rpm, 7-zip, and ISO 9660 cdrom images and can create tar, pax, cpio, ar, zip, 7-zip, and shar archives.
passwd
modify a user's password: The passwd utility changes the user's password. If the user is not the super-user, passwd first prompts for the current password and will not continue unless the correct password is entered.
mv
move files
zip
package and compress (archive) files: zip is a compression and file packaging utility for Unix, VMS, MSDOS, OS/2, Windows 9x/NT/XP, Minix, Atari, Macintosh, Amiga, and Acorn RISC OS. It is analogous to a combination of the Unix commands tar(1) and com- press(1) and is compatible with PKZIP (Phil Katz's ZIP for MSDOS systems).
awk
pattern-directed scanning and processing language: Awk scans each input file for lines that match any of a set of patterns specified literally in prog or in one or more files specified as -f progfile. With each pattern there can be an associated action that will be performed when a line of a file matches the pattern. Each line is matched against the pattern portion of every pattern-action statement; the associated action is performed for each matched pattern. The file name - means the standard input. Any file of the form var=value is treated as an assignment, not a file- name, and is executed at the time it would have been opened if it were a filename. The option -v followed by var=value is an assignment to be done before prog is executed; any number of -v options may be present. The -F fs option defines the input field separator to be the regular expression fs.
tee
pipe fitting: The tee utility copies standard input to standard output, making a copy in zero or more files. The output is unbuffered.
pwd
present working directory
ps
process status The ps utility displays a header line, followed by lines containing information about all of your processes that have controlling terminals.
info
read Info documents: Read documentation in Info format.
rmdir
remove directory
rm
remove directory entries: The rm utility attempts to remove the non-directory type files specified on the command line. If the permis- sions of the file do not permit writing, and the standard input device is a terminal, the user is prompted (on the standard error output) for confirmation.
id
return user identity: The id utility displays the user and group names and numeric IDs, of the calling process, to the standard output. If the real and effective IDs are different, both are displayed, otherwise only the real ID is displayed.
find
search for files in a directory hierarchy
scp
secure copy (remote file copy program): scp copies files between hosts on a network. It uses ssh(1) for data transfer, and uses the same authentica- tion and provides the same security as ssh(1). scp will ask for passwords or passphrases if they are needed for authentication. The source and target may be specified as a local pathname, a remote host with optional path in the form [user@]host:[path], or a URI in the form scp://[user@]host[:port][/path]. Local file names can be made explicit using absolute or relative pathnames to avoid scp treating file names containing `:' as host speci-fiers.
send and receive mail: The mail utility is an intelligent mail processing system, which has a command syntax reminiscent of ed(1) with lines replaced by messages.
hostname
set or print name of current host system: The hostname utility prints the name of the current host. The super-user can set the hostname by supplying an argument. To keep the hostname between reboots, run `scutil --set HostName name-of-host'.
groups
show group memberships: The groups utility has been obsoleted by the id(1) utility, and is equivalent to ``id -Gn [user]''. The command ``id -p'' is suggested for normal interactive use. The groups utility displays the groups to which you (or the optionally specified user) belong.
uptime
show how long system has been running: The uptime utility displays the current time, the length of time the system has been up, the number of users, and the load average of the system over the last 1, 5, and 15 minutes.
netstat
show network status: The netstat command symbolically displays the contents of various network-related data structures. There are a number of output formats, depending on the options for the information presented. The first form of the command displays a list of active sockets for each protocol. The second form presents the contents of one of the other network data structures according to the option selected. Using the third form, with a wait interval specified, netstat will continuously display the information regarding packet traffic on the configured network interfaces. The fourth form displays statistics for the specified protocol or address family. If a wait interval is specified, the protocol information over the last interval seconds will be displayed. The fifth form displays per-interface statistics for the specified protocol or address family. The sixth form displays mbuf(9) statistics. The seventh form displays routing table for the specified address family. The eighth form displays routing statistics.
sort
sort or merge records (lines) of text and binary files
sed
stream editor: The sed utility reads the specified files, or the standard input if no files are specified, modifying the input as specified by a list of commands. The input is then written to the standard output.
su
substitute user identity: The su utility requests appropriate user credentials via PAM and switches to that user ID (the default user is the superuser). A shell is then executed.
sudo
sudo allows a permitted user to execute a command as the superuser or another user, as specified by the security policy. The invoking user's real (not effective) user-ID is used to determine the user name with which to query the security policy.
kill
terminate or signal a process: The kill utility sends a signal to the processes specified by the pid operands. Only the super-user may send signals to other users' processes.
tr
translate characters
touch
update or create file
wc
word, line, character, and byte count: The wc utility displays the number of lines, words, and bytes contained in each input file, or standard input (if no file is specified) to the standard output. A line is defined as a string of characters delimited by a <newline> character. Characters beyond the final <newline> character will not be included in the line count.
echo
write arguments to the standard output: The echo utility writes any specified operands, separated by single blank (` ') characters and followed by a newline (`\n') character, to the standard output.