A
alias
The alias command lets you run a command or a series of Unix commands using a shorter name than the ones usually associated with them.
apt, apt-get
The apt-get tool automatically updates a Debian machine and installs Debian packages/programs.
awk, Gawk
AWK is a programming language tool used to manipulate text. The AWK utility resembles the shell programming language in many areas, but AWK’s syntax is very much its own. Gawk is the GNU Project’s version of the AWK programming language.
B
bzip2
A portable, fast, open source program that compresses and decompresses files at a high rate, but that does not archive them.
C
cat
A Unix/Linux command that can read, modify, or concatenate text files. The cat command also displays the contents of a file.
cd
The cd command changes the current directory in Linux and can be used to toggle between directories conveniently. The Linux cd command is similar to the MS-DOS CD and CHDIR commands.
chmod
The chmod command changes the permissions of one or more files. Only the file owner or a privileged user can change the access mode.
chown
The chown prompt changes file or group ownership. It gives admins the option to change ownership of all objects in a directory tree, as well as to view information about the objects processed.
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, cmp reports the byte and line number where the first difference occurred.
comm
Admins use comm to compare sorted files. The output is in three columns, from left to right: lines unique to file1, lines unique to file2, and lines common to both files.
cp
The cp command copies files and directories. Copies can be made to another directory simultaneously, even if the copy is under a different name.
cpio
The cpio command copies files into or out of a cpio or tar archive. A tar archive is a file that contains other files, along with information about them, such as their file names, owners, timestamps, and access permissions. The archive can be another file on the disk, a magnetic tape, or a pipe. It also has three operating modes: copy-out, copy-in, and copy-pass. It is also a more efficient alternative to tar.
CRON
CRON is a Linux system process that executes a program at a preset time. To use a CRON script, admins must prepare a text file that describes the program and when they want CRON to execute it. Then, the crontab program loads the text file and executes the program at the specified time.
cURL
Admins use cURL to transfer a URL. It helps determine whether an application can reach another service and how healthy that service is.
D
declare
The declare command declares variables, assigns attributes to them, or modifies their properties.
df
This command displays the amount of disk space available on the file system containing each file name argument. Without a file name, the df command shows the available space on all currently mounted file systems.
E
echo
Use echo to repeat a string variable to standard output.
enable
The enable command stops or starts printers and classes.
env
The env command runs a program in a modified environment or displays the current environment and its variables.
eval
The eval command analyzes several arguments, concatenates them into a single command, and reports the status of that command.
exec
This function replaces the parent process with the command typed subsequently. The exec command treats its arguments as the specification of one or more subprocesses to execute.
exit
The exit command terminates a script and returns a value to the parent script.
expect
The expect command talks to other interactive programs via a script and waits for a response, often from any string that matches a given pattern.
export
The export command converts a file to a different format. Once a file is exported, it can be accessed by any application that uses the new format.
F
find
The find command searches the directory tree to locate files that meet specified conditions, including -name, -type, -exec, -size, -mtime, and -user.
for, while
The for and while commands execute or loop items repeatedly as long as certain conditions are met.
free
With the free command, admins can see the total amount of free and used physical memory and swap space, as well as the buffers and cache used by the kernel.
G
gawk
See AWK.
grep
The grep command searches files for a given character string or pattern and can replace the string with another. This is one method of searching for files within Linux.
gzip
This is the GNU Project’s open-source program for file compression that compresses webpages on the server for decompression in the browser. This is popular for streaming media compression and can simultaneously concatenate and compress several streams.
H
history
The history function shows all the commands used since the start of the current session.
I
ifconfig
The iconfig command configures kernel-resident network interfaces at boot time. It is usually only needed when debugging or during system tuning.
ifup
With ifup, admins can configure a network interface and enable a network connection.
ifdown
The ifdown command shuts down a network interface and disables a network connection.
iptables
The iptables command allows or blocks traffic on a Linux host and can prevent specific applications from receiving or transmitting a request.
K
kill
With kill signals, admins can send a specific signal to a process. It is most often used to shut down processes or applications safely.
L
less
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 navigation available.
locate
The locate command reads one or more databases and writes file names to match specific output patterns.
lft
The lft command determines connection routes and provides information for debugging connections or finding a box/system location. It also displays route packets and file types.
ln
The ln command creates a new name for a file using hard links, allowing multiple users to share a single file.
ls
The ls command lists files and directories in the current working directory, allowing admins to see when configuration files were last edited.
lsof
Admins use lsof to list all the open files. They can add -u to find the number of open files for a given username.
lsmod
The lsmod command displays a module’s status within the kernel, which helps troubleshoot server function issues.
M
man
The man command allows admins to format and display the user manual that’s built into Linux distributions, which documents commands and other system aspects.
more
Similar to less, more pages through text one screen at a time, but has limitations on file navigation.
mount
This command mounts file systems on servers. It also lists the current file systems and their mount points, which helps locate a defunct drive or install a new one.
mkdir
Linux’s mkdir command creates a new directory with a given path.
N
neat
A Gnome GUI tool that allows admins to specify the information needed to set up a network card.
netconfig/netcfg
Admins can use netconfig to configure a network, enable network products and display a series of screens that ask for configuration information.
netstat
This command provides information and statistics about protocols in use and current TCP/IP network connections. It is a helpful forensic tool for identifying which processes and programs are active on a computer and involved in network communications.
nslookup
A user can enter a hostname and find the corresponding IP address with nslookup. It can also help find the hostname.
O
od
The od command dumps binary files in octal, hex, or binary format to standard output.
P
passwd
Admins use passwd to update a user’s current password.
ping
The ping command verifies that a particular IP address exists and is reachable. It can test connectivity and determine response time, as well as verify that a user’s host computer is operational.
ps
Admins use ps to report the statuses of current processes in a system.
pwd
The print working directory (pwd) command displays the name of the current working directory.
R
read
The read command interprets lines of text from standard input and assigns values of each field in the input line to shell variables for further processing.
rsync
This command syncs data from one disk or file to another across a network connection. It is similar to rcp, but has more options.
S
screen
The GNU screen utility is a terminal multiplexer that allows a user to run multiple terminal applications or windows from a single terminal window.
sdiff
Admins use sdiff to compare two files and produce a side-by-side listing of lines that differ. The command then merges the files and outputs the results to the outfile.
sed
The sed utility is a stream editor that filters text in a pipeline, distinguishing it from other editors. It takes text input, performs operations on it, and outputs the modified text. This command is typically used to extract part of a file using pattern matching or to substitute multiple occurrences of a string within a file.
service
This command is the quickest way to start or stop a service, such as networking.
shutdown
The shutdown command turns off the computer and can be combined with options such as -h to halt after shutdown or -r to reboot after shutdown.
slocate
Like locate, slocate, or secure locate, provides a way to index and quickly search for files. Still, it can also securely store file permissions and ownership to hide information from unauthorized users.
Snort
Snort is an open source network intrusion detection system and packet sniffer that monitors network traffic. It looks at each packet to detect dangerous payloads or suspicious anomalies. Snort is based on libpcap.
sort
This command sorts lines of text alphabetically or numerically according to the fields. Users can input multiple sort keys.
sudo
The sudo command lets a system admin grant certain users the ability to run some — or all — commands at the root level, and logs all commands and arguments.
SSH
SSH is a command-line interface for secure remote access to computers and is used by network admins to control servers remotely.
T
tar
The tar command lets users create archives from specified files or extract files from a specific archive.
tail
The tail command displays the last few lines of the file. This is particularly helpful for troubleshooting code, since admins don’t often need all possible logs to identify code errors.
TOP
TOP is a set of network protocols that perform distributed information processing and display the system tasks that consume the most memory. TOP can sort tasks by CPU usage, memory usage, and runtime.
touch
Admins can create a blank file within Linux with the touch command.
tr
This command translates or deletes characters from a text stream. It writes to a standard output, but it does not accept file names as arguments — it only accepts input from standard input.
traceroute
The traceroute function determines and records a route through the Internet between two computers and helps troubleshoot network/router issues. If the domain name does not work or is unavailable, admins can use traceroute to trace the IP address.
U
uname
This function displays the current operating system name and can print system information.
uniq
With uniq, admins can compare adjacent lines in a file and remove or identify any duplicate lines.
V
vi
The vi environment is a text editor that allows a user to control the system solely with the keyboard, rather than both mouse selections and keystrokes.
vmstat
The vmstat command snapshots the state of a system and reports information on processes, memory, paging, and CPU activity. This is a suitable method for admins to use to determine where issues/slowdowns may occur in a system.
W
wget
This is a network utility that retrieves web files that support HTTP, HTTPS and FTP protocols. The wget command works non-interactively in the background when a user is logged off. It can create local versions of remote websites and recreate original site directories.
while
See for.
whoami
The whoami command prints the user login associated with the current user ID to standard output.
X
xargs
Admins use xargs to read, build, and execute arguments from standard input. Blanks separate each input.
Original: https://searchdatacenter.techtarget.com/tutorial/77-Linux-commands-and-utilities-youll-actually-use
Useful information:
https://searchdatacenter.techtarget.com/tip/The-top-Linux-commands-for-server-administrators
https://searchdatacenter.techtarget.com/tip/Six-helpful-Linux-networking-commands-to-monitor-connectivity
https://searchdatacenter.techtarget.com/answer/Two-Linux-and-Unix-commands-you-might-not-know-you-need