alias
A way to run a command or a series of Unix commands using a shorter name you get associated with such commands.
How to use the
alias command in Linux.
apt-get
Apt-get is a tool to automatically update a
Debian machine and get and install Debian packages/programs.
How to manage software on Ubuntu Server with "aptitude" and "apt-get".
Understanding the Debian archives and apt-get.
Using apt-get to
update your Debian Machine.
Aspell
GNU Aspell is a free and open source
spell checker designed to replace
Ispell. It can either be used as a library or as an independent spell checker.
How to use Aspell to check spelling.
AWK,
Gawk
A programming-language tool used to manipulate text. The language of the
AWK utility resembles the shell-programming language in many areas, although AWK's syntax is very much its own.
Learn how to
use the AWK utility.
Gawk is the GNU Project's version of the
AWK programming language.
bzip2
A portable, fast open source program used to compress and decompress files at high rates.
How to use
bzip2 in Linux.
More on
how to use the bzip2 compression program.
cat
A Unix/Linux command that can read, modify or concatenate
text files, most commonly used for displaying contents of files.
See how to
use cat to display contents of a file in Linux.
An article on
what you can do with the cat command.
cd
The cd command changes the
current directory in Linux, and can toggle between directories conveniently. It is similar to the CD and
CHDIR commands in MS-DOS.
See more on
how to use the cd command to change directories.
chmod
Chmod changes the access mode (permissions) of one or more files. Only the owner of a file or a privileged user may change the mode.
See examples of changing the permissions of files
using chmod.
chown
Chown changes file or group ownership, and has options to change ownership of all objects within a directory tree, and view information on objects processed.
Learn how to change
file ownership with chown.
cmp
The cmp utility compares two files of any type and writes the results to the
standard output. By default, cmp is silent if the files are the same; if they differ, the byte and line number at which the first difference occurred is reported.
See
IBM's examples for using cmp.
comm
Comm compares lines common to the sorted files file1 and file2. Output is in three columns, from left to right: lines unique to file1, lines unique to file2, and lines common to both files.
More on
comparing lines with comm.
Read a brief
tutorial on using comm.
cp
The cp command copies files and directories, and copies can be made simultaneously to another directory if the copy is under a different name.
Find out how to
copy Linux files and directories with the cp command.
cpio
Cpio copies files into or out of a
cpio or tar archive, which is a file that contains other files plus information about them, such as their file name, owner, timestamps, and access permissions. The archive can be another file on the disk, a magnetic tape, or a pipe. Cpio has three operating modes, and is a more efficient alternative to tar.
Learn how to use
cpio when moving files in a Unix-to-Linux port.
See how to
back up files with cpio.
CRON
CRON is a Linux system process that will execute a program at a preset time. To use
CRON, a user must prepare a text file that describes the program to be executed and the times that CRON should execute them. Then, the crontab program is used to load the text file that describes the
CRON jobs into
CRON.
Using
CRON to execute programs at specific times.
date
Date sets a system's date and time. Also a useful way to output/print current information when working in a script file.
A few more
examples from IBM on setting date and time with date.
declare
Declare declares variables, gives them attributes, or modifies properties of variables.
Examples of
declaring variables with declare.
df
Df displays the amount of disk space available on the file system containing each file name argument. With no file name, available space on all currently mounted
file systems is shown.
More on
using df to display the amount of disk space available.
echo
Echo allows a user to repeat, or "echo," a string variable to
standard output.
More on
using the Echo command with shell scripts.
enable
Enable will stop or start printers or classes.
Examples of how to
enable LP printers.
env
Env runs a program in a modified environment, or displays the current environment and its variables.
Examples of
changing environment variables using env.
eval
Eval evaluates several arguments and concatenates them into a single command, and then reports on that argument's status.
More on
concatenating arguments with eval.
exec
Exec replaces the
parent process by whatever command is typed. This command treats its arguments as the specification of one or more sub processes to execute.
More examples of
replacing parent processes with exec.
exit
The exit command terminates a script, and can return a value to the parent script.
More on
terminating scripts with exit.
expect
Expect talks to other interactive programs according to a script, and waits for a response, often from any string that matches a given pattern.
Using
expect for responses.
export
Export converts files into another format than the one it is currently in. Once a file is exported, it can be accessed by any application that uses the format.
Examples of
exporting data from a database with export.
find
Find searches the directory tree to find particular groups of files that meet specified conditions, including --name and --type, -exec and --size, and --mtime and --user.
Efficiently
locating files with find.
for,
while
For and while are used to execute or loop items repeatedly as long as conditions are met.
More on
looping items with the for command.
More on
looping items with the while command.
free
Free displays the total amount of free and used physical memory and
swap space in the system, as well as the buffers and cache used by the kernel.
Learn
how to use the free command to optimize a computer's memory.
gawk
See
AWK.
grep
Grep searches file(s) for a given character string or pattern, and can replace the string with another one. One method of searching for files within Linux.
Examples of
searching with grep.
gzip
Gzip is the GNU project's open source program used for
file compression, compressing web pages on the server end for decompression in the browser. Popular for streaming media compression, and can concatenate and compress several streams simultaneously.
Examples of
using gzip for compressing files.
ifconfig
Ifconfig is used to configure the kernel-resident network interfaces. It is used at
boot time to set up interfaces. After that, it is usually only needed when debugging or when system tuning is needed.
Examples of
using iconfig to configure a network.
Using
ifconfig to detect Linux network configuration problems.
ifup
Ifup configures a network interface/enables a network connection.
More on the
ifup command in configuring network interfaces.
ifdown
Ifdown shuts down a network interface/disables a network connection.
More on shutting down networks
with ifdown.
less,
more
The less command lets an admin scroll through configuration and
error log files, displaying
text files one screen at a time, with backward or forward moving available in files. More mobility within files than in more.
View several different file types
with less.
Similar to less, more pages through text one screen at a time, but is more limited in moving in files.
See a
few examples of displaying files with more.
locate,
slocate
Locate reads one or more databases and writes file names matching patterns to output.
Finding files/directories efficiently
with locate.
Like locate, slocate, or secure locate, provides a way to index and quickly search for files, but also securely stores
file permissions and ownership so unauthorized users will be unable to view such files.
See
an example of using slocate as a quick secure way to index files.
lft
Lft is similar to
traceroute in determining connection routes, but gives a lot more information for debugging connections or finding where a box/system is. It displays route packets and file types.
More on
displaying route packets with lft.
ln
The ln command creates new names for a file by hard linking, letting multiple users share one file.
Examples of
hard linking files with ln.
A few more
examples of using ln.
ls
The ls command lists files and directories within the current
working directory, and admins can determine when
configuration files were last edited.
The ls command is also discussed in
this tip.
Examples of
listing files and directories with ls.
man
Short for "manual," man allows a user to format and display the user manual built into Linux distributions, which documents commands and other aspects of the system.
The man command is also discussed in
this tip.
See how to use the
man command.
See
examples of formatting man pages.
mc
A visual shell, text-based
file manager for Unix systems.
An extensive guide to
managing files with mc.
more
See less.
neat
Neat is a GNOME GUI
admin tool which allows admins to specify information needed to set up a
network card, among other features.
Setting up an NTL Cable Modem
using neat.
Where
neat falls in when building a network between Unix and Linux systems.
netconfig, netcfg
Netconfig configures a network, enables network products and displays a series of screens that ask for configuration information.
Configuring networks
using Red Hat netcfg.
netstat
Netstat provides information and statistics about protocols in use and current TCP/IP network connections. A helpful forensic tool in figuring out which processes and programs are active on a computer and involved in networked communications.
More on checking network statuses
with the netstat command.
nslookup
Nslookup allows a user to enter a host name and find the corresponding IP address. A reverse of the process to find the host name is also possible.
More
from Microsoft on how to find IP addresses with
nslookup.
od
Od is used to dump
binary files in octal (or hex, binary) format to
standard output.
Examples of
dumping files with od.
More on od
from IBM.
passwd
Passwd updates a user's authentication tokens (changes the current password).
Some
IBM examples on changing passwords with passwd.
ping
Ping allows a user to verify that a particular IP address exists and can accept requests. Can be used to test connectivity and determine response time, and ensure that a host computer the user is trying to reach is actually operating.
Examples
from IBM of using ping to verify IP addresses.
ps
Ps reports statuses of current processes in a system.
Some examples of using the
ps command.
pwd
The
pwd (print
working directory) command displays the name of the current
working directory. A basic Linux command.
Learn the
differences between $ PATH and pwd.
Using
pwd to print the current working directory.
read
Read is used to read lines of text from
standard input and assign values of each field in the input line to shell variables for further processing.
Examples
from IBM on using read.
RPM
Red Hat
Package Manager (RPM) is a
command-line driven program capable of installing, uninstalling and managing software packages in Linux.
A
white paper on using RPM.
The Differences of
yum and RPM.
Examples of
installing packages with RPM.
rsync
Rsync synchs data from one disk or file to another across a network connection. Similar to rcp, but has more options.
A tip on
backing up data with rsync.
How to use
rsync to back up a directory in Linux.
screen
The
GNU screen utility is a terminal multiplexor in which a user can use a single
terminal window to run multiple terminal applications or windows.
A
tutorial on running multiple windows and other uses of screen.
A tip on the
uses of screen.
sdiff
Sdiff finds differences between two files by producing a side-by-side listing indicating lines that are different. It then merges the files and outputs results to outfile.
Example of
contrasting files with sdiff.
More
examples from IBM on the sdiff command.
sed
Sed is a
stream editor that is used to filter text in a pipeline, distinguishing it from other editors.
Sed takes text input and performs operation(s) on it and outputs the modified text. Typically used for extracting part of a file using pattern matching or substituting multiple occurrences of a string within a file.
More on
extracting and replacing parts of a file with sed.
Several more
examples from IBM on using sed for filtering.
shutdown
Shutdown is a command that turns off the computer and can be combined with variables such as -h for halt after shutdown or -r for reboot after shutdown.
Shut down or halt a computer
with shutdown.
slocate
See locate.
Snort
Snort is an open source
network intrusion detection system and
packet sniffer that monitors network traffic, looking at each packet to detect dangerous payloads or suspicious anomalies. Based on libpcap.
Stopping hackers
with Snort.
More
from Red Hat on using Snort.
sort
Used to sort lines of text alphabetically or numerically according to fields; supports multiple sort keys.
Examples of
sorting through lines of text with the sort command.
More
examples of sort with multiple sort keys.
sudo
Sudo allows a
system admin to give certain users the ability to run some (or all) commands at the root level, and logs all commands and arguments.
A
tutorial on giving permissions to users with the
sudo command.
SSH
SSH is a command interface used for securely gaining access to a remote computer, and is used by network admins to control servers remotely.
A
comprehensive tutorial on secure access to remote computers with
SSH.
tar
The tar program provides the ability to create archives from a number of specified files, or extract files from such an archive.
Examples of
creating archives with tar.
TOP
TOP is a set of protocols for networks that perform distributed information processing in offices, and it displays the tasks on the system that take up the most memory. TOP can sort tasks by CPU usage, memory usage and runtime.
Monitoring system processes
with TOP.
tr
Used to translate or delete characters from a text stream, writing to
standard output, but does not accept file names as arguments -- only inputs from
standard input.
Examples
from IBM of translating characters with tr.
traceroute
Traceroute determines and records a route through the Internet between two computers and is useful for troubleshooting network/router issues. If the domain does not work or is not available, an IP can be tracerouted.
A tutorial on
using traceroute to determine network issues.
uname
Uname displays the name current operating system, and can print information about the mentioned system.
Examples of viewing information on the current operating system
with uname.
uniq
Uniq compares adjacent lines in a file, and removes/reports any duplicated lines. Removing duplicate lines
with the uniq command.
A
tip from IBM on removing redundant lines with
uniq.
vi
Vi is a text editor that allows a user to control the system by solely using the keyboard instead of a combination of mouse selections and keystrokes.
An entire
guide to using vi to easily control a system with the keyboard.
vmstat
Vmstat is used to get a snapshot of everything in a system, reporting information on such items as processes, memory, paging, and cpu activity. A good method for admins in determining where issues/slowdown in a system may be occurring.
How to
keep an eye on Linux performance with vmstat and others.
Examples of
viewing system memory usage with vmstat.
wc
wc counts the number of words, lines and characters of
text files, and produces a count for multiple files if several files are selected.
More
from IBM on displaying word counts with wc.
wget
Wget is a
network utility that retrieves files from the Web supporting http, https and ftp protocols. It works non-interactively, in the background, while a user is logged off. Can create local versions of remote websites, re-creating directories of original sites.
Examples of
creating mirror images of sites with wget.
while
See for.
whoami
Whoami prints or writes the user/login name associated with the current user ID to the standard output.
Examples
from IBM of determining which login name is used with
whoami.
xargs
Xargs reads, builds and executes arguments from standard input. Blank lines in the input are ignored.
Examples
from IBM of running commands from input with
xargs.
symbol) and the "c" key at the same time copies whatever is currently selected (text, graphics, and so forth) into the Clipboard. This is also known as the Command-C key combination (or keyboard shortcut).
)
(Control key)
(
(Shift key)
(