Beginner

 1. ls – List Directory Contents

The ls command is one of the most frequently used Linux commands. It lists the contents of a directory, showing all files and subdirectories contained inside.

Without any options or arguments, ls will display the contents of the current working directory. You can pass a path name to list files and folders in that location instead.

Syntax:

ls -l /home/user/documents

Some of the most useful ls options include:

-l – Display results in long format, showing extra details like permissions, ownership, size, and modification date for each file and directory.

-a – Show hidden files and directories that start with . in addition to non-hidden items.

-R – Recursively list all subdirectory contents, descending into child folders indefinitely.

-S – Sort results by file size, largest first.

-t – Sort by timestamp, newest first

2. cd – Change Directory

The cd command is used to navigate between directories. It allows you to move the current working directory to a new location in the filesystem.

When you run the cd command by itself, it will return you to the home directory. You can also pass a specific path to change into. For example:

cd /usr/local – Changes to the /usr/local directory.

cd .. – Moves up one level to the parent directory.

cd ~/pictures – Changes to the pictures folder in your home directory.

Syntax:

cd [directory]

Example:

cd /home/user/documents

This would change the working directory to the “documents” folder under /home/user. Using cd is essential for being able to access and work with files in different locations conveniently.

3. mkdir – Create A New Directory

The mkdir command allows you to create a new folder. You simply pass the name of the directory to create.

Syntax:

mkdir [options] <directory>

This will create a directory called “newproject” in the current working directory.

Some useful mkdir options:

-p – Creates parent directories recursively as needed.

-v – Verbose output showing created directories.

Example:

mkdir -v ~/project/code

This would create the “code” subdirectory under “project” in the user’s home folder, with verbose output showing the directory being created.

4. rmdir – Remove Directory

To delete an empty directory, use the rmdir command. Note that rmdir can only remove empty directories – we’ll need the rm command to delete non-empty ones.

Syntax:

rmdir [options] <directory>

Some options for rmdir include:

-v – Verbose output when deleting directories.

-p – Remove parent directories recursively as needed.

Example:

rmdir -v ~/project/code

This would delete the “code” subdirectory under “project” while showing verbose output.

5. touch – Create A New Empty File

The touch command is used to create a new empty file instantly. This is useful when you need an empty file to populate with data later.

The basic syntax of touch is:

touch [options] filename

Some useful options for touch include:

-c – Do not create the file if it already exists. This avoids accidentally overwriting existing files.

-m – Instead of creating a new file, update the timestamp on an existing file. This can be used to change the modified time.

For example:

touch /home/user/newfile.txt

The above command creates a new empty file called “newfile.txt” in the user’s /home/user directory. If newfile.txt already exists, it will update the access and modification times on the file instead.

6. cp – Copy Files And Directories

The cp command copies files or directories from one location to another. It requires passing a source path and a destination.

The basic syntax of cp is:

cp [options] source destination

Some useful cp options:

-r – Copy directories recursively, descending into child directories to copy their contents as well. Necessary when copying directories.

-i – Prompt before overwriting any existing files at the destination. It prevents accidentally overwriting data.

-v – Display verbose output showing the details of each file as it is copied. Helpful to confirm exactly what was copied.

For example:

cp -r /home/user/documents /backups/

This would recursively copy the /home/user/documents directory and all its contents to the /backups/ directory. The -r option is needed to copy directories.

The cp command is one of the most frequently used file management utilities for copying files and directories in Linux. You’ll find yourself using this command quite often.

7. mv – Move Or Rename Files And Directories

The mv command is used to move files or directories to a different location or rename them. Unlike copy, the files from the source path are deleted after they’ve been moved to the destination.

You can also use the mv command to rename files since you simply need to change the source and destination paths to the old and new name.

The syntax of mv is:

mv [options] source destination

Useful mv options:

-i – Prompt before overwriting any existing files at the destination location. This prevents accidentally overwriting data.

-v – Produce verbose output showing each file or directory as it is moved. This is helpful for confirming exactly what was moved.

For example:

mv ~/folder1 /tmp/folder1

The above will move folder1 from the home (~) directory to the /tmp/ directory. Let’s look at another example of using the mv command for renaming files.

mv folder1 folder2

Here, “folder1” is renamed to “folder2.”

8. rm – Remove Files And Directories

The rm command deletes files and directories. Use caution because deleted files and directories cannot be recovered.

The syntax is:

rm [options] name

Useful rm options:

-r – Recursively delete directories, including all contents inside them. This is necessary when deleting directories.

-f – Force deletion and suppress all confirmation prompts. This is a dangerous command, as files cannot be recovered when they’re gone!

-i – Prompt for confirmation before deleting each file or directory, which provides safety against accidental removal.

For example:

rm -rf temp

This recursively deletes the “temp” directory and all its contents without prompting (-f overrides confirmations).

Note: The rm command permanently erases files and folders, so use it with extreme care. If used with sudo privileges, you could also delete the root directory completely, and Linux would no longer function after restarting your computer. 

9. find – Search For Files In A Directory Hierarchy

The find command recursively searches directories for files matching given criteria.

The basic syntax of find is:

find [path] [criteria]

Some useful criteria options for find include:

-type f – Search for only normal files, omitting directories.

-mtime +30 – Search for files modified over 30 days ago.

-user jane – Search for files belonging to user “jane.”

For example:

find . -type f -mtime +30

This will find all regular files over 30 days old under the current directory (denoted by the dot).

The find command allows searching for files based on all kinds of advanced conditions like name, size, permissions, timestamps, ownership, and more.

10. du – Estimate File Space Usage

The du command measures the file space usage for a given directory. When used without options, it displays disk usage for the current working directory.

The syntax for du is:

du [options] [path]

Useful du options:

-h – Display file sizes in human-readable format like K for Kilobytes rather than a byte count. Much easier to parse.

-s – Only show the total size for a directory, rather than listing each subdirectory and file. Good for summary.

-a – Show individual file sizes in addition to totals. Helps identify large files.

For example:

du -sh pictures

This will print a human-readable size total for the “pictures” directory.

The du command is helpful for analyzing disk usage for a directory tree and identifying files consuming excessive space.

11. grep – Search Text Using Patterns

The grep command is used to search for text patterns within files or output. It prints any lines that match the given regular expression. grep is extremely powerful for searching, filtering, and pattern matching in Linux.

Here is the basic syntax:

grep [options] pattern [files]

For example:

grep -i "error" /var/log/syslog

This searches the syslog file for the word “error,” ignoring case sensitivity.

Some useful grep options:

-i – Ignore case distinctions in patterns

-R – Recursively search subdirectories

-c – Print only a count of matching lines

-v – Invert match, print non-matching lines

grep allows you to search files and output for keywords or patterns quickly. It’s invaluable for parsing logs, searching source code, matching regexes, and extracting data.

14. sort – Sort Lines Of Text Files

When you’re working with a lot of text or data or even large outputs from other commands, sorting it is a great way to make things manageable. The sort command will sort the lines of a text file alphabetically or numerically.

Basic sort syntax:

sort [options] [file]

Useful sort options:

-n – Sort numerically instead of alphabetically

-r – Reverse the sort order

-k – Sort based on a specific field or column

For example:

sort -n grades.txt

This numerically sorts the contents of grades.txt. sort is handy for ordering the contents of files for more readable output or analysis.

15. uniq – Report Or Omit Repeated Lines

The uniq command filters duplicate adjacent lines from input. This is often used in conjunction with sort.

Basic syntax:

uniq [options] [input]

Options:

-c – Prefix unique lines with count of occurrences.

-d – Only show duplicated lines, not unique ones.

For example:

sort data.txt | uniq

This will remove any duplicated lines in data.txt after sorting. uniq gives you control over filtering repeated text.

16. diff – Compare Files Line By Line

The diff command compares two files line-by-line and prints the differences. It’s commonly used to show changes between versions of files.

Syntax:

diff [options] file1 file2

Options:

-b – Ignore changes in whitespace.

-B – Show differences inline, highlighting changes.

-u – Output differences with three lines of context.

For example:

diff original.txt updated.txt

This will output the lines that differ between original.txt and updated.txt. diff is invaluable for comparing revisions of text files and source code.

17. wc – Print Line, Word, And Byte Counts

The wc (word count) command prints counts of lines, words, and bytes in a file.

Syntax:

wc [options] [file]

Options:

-l – Print only the line count.

-w – Print only the word count.

-c – Print only the byte count.

For example:

wc report.txt

This command will print the number of lines, words, and bytes in report.txt.

18. > – Redirect Standard Output

The > redirection operator redirects the standard output stream from the command to a file instead of printing to the terminal. Any existing contents of the file will be overwritten.

For example:

ls -l /home > homelist.txt

This will execute ls -l to list the contents of the /home directory.

Then, instead of printing that output to the terminal, the > symbol captures that standard output and writes it to homelist.txt, overwriting any existing file contents.

Redirecting standard output is helpful for saving command results to files for storage, debugging, or chaining commands together.

19. >> – Append Standard Output

The >> operator appends standard output from a command to a file without overwriting existing contents.

For example:

tail /var/log/syslog >> logfile.txt

This will append the last 10 lines of the syslog log file onto the end of logfile.txt. Unlike >, >> adds the output without erasing the current logfile.txt contents.

Appending is helpful in collecting command output in one place without losing existing data.

20. < – Redirect Standard Input

The < redirection operator feeds a file’s contents as standard input to a command, instead of taking input from the keyboard.

For example:

wc -l < myfile.txt

This sends the contents of myfile.txt as input to the wc command, which will count lines in that file instead of waiting for keyboard input.

Redirecting input is useful for batch-processing files and automating workflows.

21. | – Pipe Output To Another Command

The pipe | operator sends the output from one command as input to another command, chaining them together.

For example:

ls -l | less

This pipes the output of ls -l into the less command, which allows scrolling through the file listing.

Piping is commonly used to chain together commands where the output of one feeds the input of another. This allows building complex operations out of smaller single-purpose programs.

Archive Commands

Archiving commands allow you to bundle multiple files and directories into compressed archive files for easier portability and storage. Common archive formats in Linux include .tar, .gz, and .zip.

23. tar – Store And Extract Files From An Archive

The tar command helps you work with tape archive (.tar) files. It helps you bundle multiple files and directories into a single compressed .tar file.

Syntax:

tar [options] filename

Useful tar options:

-c – Create a new .tar archive file.

-x – Extract files from a .tar archive.

-f – Specify archive filename rather than stdin/stdout.

-v – Verbose output showing archived files.

-z – Compress or uncompress archive with gzip.

For example:

tar -cvzf images.tar.gz /home/user/images

This creates a gzip-compressed tar archive called images.tar.gz containing the /home/user/images folder.

30. sftp – Secure File Transfer Program

The sftp program provides interactive file transfers over SSH, similar to regular FTP but encrypted. It can transfer files to/from remote systems.

sftp connects to a host then accepts commands like:

sftp user@host

get remotefile localfile

put localfile remotefile

This retrieves remotefile from the server and copies localfile to the remote host.

sftp has an interactive shell for navigating remote file systems, transferring files and directories, and managing permissions and properties.

31. wget – Retrieve Files from the Web

The wget tool downloads files over HTTP, HTTPS, and FTP connections. It’s useful for retrieving web resources directly from the terminal.

For example:

wget https://example.com/file.iso

This downloads the file.iso image from the remote server.

Useful wget options:

-c – Resume interrupted download.

-r – Download recursively.

-O – Save to specific filename.

wget is ideal for scripting automatic downloads and mirroring websites.

32. curl – Transfer Data From Or To A Server

The curl command transfers data to or from a network server using supported protocols. This includes REST, HTTP, FTP, and more.

For example:

curl -L https://example.com

The above command retrieves data from the HTTPS URL and outputs it.

Useful curl options:

-o – Write output to file.

-I – Show response headers only.

-L – Follow redirects.

33. chmod – Change File Modes Or Access Permissions

The chmod command is used to change the access permissions or modes of files and directories. The permission modes represent who can read, write, or execute the file.

For example:

chmod 755 file.txt

There are three sets of permissions—owner, group, and public. Permissions are set using numeric modes from 0 to 7:

7 – read, write, and execute.

6 – read and write.

4 – read only.

0 – no permission.

This sets the owner permissions to 7 (rwx), group to 5 (r-x), and public to 5 (r-x). You can also reference users and groups symbolically:

chmod g+w file.txt

The g+w syntax adds group write permission to the file.

Setting proper file and directory permissions is crucial for Linux security and controlling access. chmod gives you flexible control to configure permissions precisely as needed.

34. chown – Change File Owner And Group

The chown command changes ownership of a file or directory. Ownership has two components—the user who is the owner, and the group it belongs to.

For example:

chown john:developers file.txt

The above example command will set the owner user to “john” and the owner group to “developers.”

Only the root superuser account can use chown to change file owners. It’s used to fix permission problems by modifying the owner and group as needed.

35. umask – Set Default File Permissions

The umask command controls the default permissions given to newly created files. It takes an octal mask as input, which subtracts from 666 for files and 777 for directories.

For example:

umask 007

New files will default to permissions 750 instead of 666, and new directories to 700 instead of 777.

Setting a umask lets you configure default file permissions rather than relying on system defaults. The umask command is useful for restricting permissions on new files without relying on someone going in and manually adding restrictions.

Process Management Commands

These commands allow you to view, monitor, and control processes running on your Linux system. This is useful for identifying resource usage and stopping misbehaving programs.

36. ps – Report A Snapshot Of Current Processes

The ps command displays a snapshot of currently running processes, including their PID, TTY, stat, start time, etc.

For example:

ps aux

This shows every process running as all users with additional details like CPU and memory usage.

Some useful ps options:

aux – Show processes for all users

--forest – Display tree of parent/child processes

ps gives you visibility into what’s currently running on your system.

37. top – Display Linux Processes

The top command shows real-time Linux process information, including PID, user, CPU %, memory usage, uptime, and more. Unlike ps, it updates the display dynamically to reflect current usage.

For example:

top -u mysql

The above command monitors processes just for the “mysql” user. It becomes quite helpful in identifying resource-intensive programs.

38. htop – Interactive Process Viewer

The htop command is an interactive process viewer replacing the top command. It shows system processes along with CPU/memory/swap usage graphs, allows sorting by columns, killing programs, and more.

Simply type in htop in the command line to view your processes.

htop has enhanced UI elements with colors, scrolling, and mouse support for easier navigation compared to top. Excellent for investigating processes.

39. kill – Send A Signal To A Process

The kill command sends a signal to a process to terminate or kill it. Signals allow graceful shutdown if the process handles them.

For example:

kill -15 12345

The above command sends the SIGTERM (15) signal to stop the process with PID 12345 gracefully.

40. pkill – Send A Signal To A Process Based On Name

The pkill command kills processes by name instead of PID. It can make things easier than finding the PID first.

For example:

pkill -9 firefox

This forcibly stops all Firefox processes with SIGKILL (9). pkill targets processes by matching name, user, and other criteria instead of the PID.

42. vmstat – Report Virtual Memory Statistics

The vmstat command prints detailed reports on memory, swap, I/O, and CPU activity. This includes metrics like memory used/free, swap in/out, disk blocks read/written, and CPU time spent on processes/idle.

For example:

vmstat 5

Other useful vmstat options:

-a – Show active and inactive memory

-s – Display event counters and memory stats

-S – Output in KB instead of blocks

5 – Output refreshed every 5 seconds.

The example above outputs memory and CPU data every 5 seconds until interrupted, which is useful for monitoring live system performance.

43. iostat – Report CPU And I/O Statistics

The iostat command monitors and displays CPU utilization and disk I/O metrics. This includes CPU load, IOPS, read/write throughput, and more.

For example:

iostat -d -p sda 5

Some iostat options:

-c – Display CPU utilization info

-t – Print timestamp for each report

-x – Show extended stats like service times and wait counts

-d – Show detailed stats per disk/partition instead of aggregate totals

-p – Display stats for specific disk devices

This shows detailed per-device I/O stats for sda every 5 seconds.

iostat helps analyze disk subsystem performance and identify hardware bottlenecks.

44. free – Display Amount Of Free And Used Memory

The free command shows the total, used and free amounts of physical and swap memory on the system. This gives an overview of available memory.

For example:

free -h

Some options for the free command:

-b – Display output in bytes

-k – Show output in KB instead of default bytes

-m – Show output in MB instead of bytes

-h – Print statistics in human-readable format like GB, MB instead of bytes.

This prints memory statistics in human-readable format (GB, MB, etc). It’s useful when you want a quick overview of memory capacity.

45. df – Report File System Disk Space Usage

The df command displays disk space usage for file systems. It shows the filesystem name, total/used/available space, and capacity.

For example:

df -h

The above command will print the disk utilization in a human-readable format. You can also run it without arguments to get the same data in block sizes.

User Management Commands

When using multi-user systems, you may need commands that help you manage users and groups for access control and permissions. Let’s cover those commands here.

47. useradd – Create A New User

The useradd command creates a new user account and home directory. It sets the new user’s UID, group, shell, and other defaults.

For example:

useradd -m john

Useful useradd options:

-m – Create the user’s home directory.

-g – Specify the primary group instead of the default.

-s – Set the user’s login shell.

The above command will create a new user, “john,” with a generated UID and home folder created at /home/john.

48. usermod – Modify A User Account

The usermod command modifies the settings of an existing user account. This can change the username, home dir, shell, group, expiry date, etc.

For example:

usermod -aG developers john

With this command, you add a user john to an additional group—“developers.” The -a appends to the existing list of groups that the user is added to.

49. userdel – Delete A User Account

The userdel command deletes a user account, home directory, and mail spool.

For example:

userdel -rf john

Helpful userdel options:

-r – Remove the user’s home directory and mail spool.

-f – Force deletion even if the user is still logged in.

This forces the removal of user “john,” deleting associated files.

Specifying options like -r and -f with userdel ensures the user account is entirely deleted even if the user is logged in or has active processes.

50. groupadd – Add A Group

The groupadd command creates a new user group. Groups represent teams or roles for permissions purposes.

For example:

groupadd -r sysadmin

Useful groupadd options:

-r – Create a system group used for core system functions.

-g – Specify the new group’s GID instead of using next available.

The above command creates a new “sysadmin” group with system privileges. When creating new groups, the -r or -g help set them up correctly.

51. passwd – Update User’s Authentication Tokens

The passwd command sets or updates a user’s authentication password/tokens. This allows changing your login password.

For example:

passwd john

This prompts user “john” to enter a new password interactively. If you’ve lost the password for an account, you may want to login to Linux with sudo or su privileges and change the password using the same method.

Networking Commands

These commands are used for monitoring connections, troubleshooting network issues, routing, DNS lookups, and interface configuration.

52. ping – Send ICMP ECHO_REQUEST To Network Hosts

The ping command verifies connectivity to a remote host by sending ICMP echo request packets and listening for echo responses.

For example:

ping google.com

53. ifconfig – Configure Network Interfaces

The ifconfig command displays and configures network interface settings, including IP address, netmask, broadcast, MTU, and hardware MAC address.

For example:

ifconfig

54. netstat – Network Statistics

The netstat command shows you the network connections, routing tables, interface stats, masquerade connections, and multicast memberships.

For example:

netstat -pt tcp

This command will output all the active TCP connections and the processes using them.

56. traceroute – Trace Route To Host

The traceroute command prints the route packets take to a network host, showing each hop along the way and transit times. Useful for network debugging.

For example:

traceroute google.com

This traces the path to reach google.com and outputs each network hop.

59. iptables – IPv4 Packet Filtering And NAT

The iptables command allows configuring Linux netfilter firewall rules to filter and process network packets. It sets up policies and rules for how the system will handle different types of inbound and outbound connections and traffic.

For example:

iptables -A INPUT -s 192.168.1.10 -j DROP

The above command will block all input from IP 192.168.1.10.

iptables provides powerful control over the Linux kernel firewall to handle routing, NAT, packet filtering, and other traffic control. It is a critical tool for securing Linux servers.

Package Management Commands

Package managers allow easy installation, update and removal of software on Linux distributions. Popular package managers include APT, YUM, DNF, Pacman, and Zypper

64. yum – Red Hat Package Manager

yum manages packages on RHEL and CentOS Linux distributions using RPM packages. It fetches from Yum repositories to install and update.

For example:

yum update

This updates all installed packages to the latest versions.

yum install httpd

The above command installs the Apache httpd package. yum has been the major package manager for keeping Red Hat distributions updated.

System Information Commands

These commands allow you to view details about your Linux system hardware, kernel, distributions, hostname, uptime, and more.

69. uname – Print System Information

The uname command prints detailed information about the Linux system kernel, hardware architecture, hostname, and operating system. This includes version numbers and machine info.

For example:

uname -a

Linux hostname 5.4.0-48-generic x86_64 GNU/Linux

uname is useful for querying these core system details. Some options include:

-a – Print all available system info

-r – Print just the kernel release number

The above command printed extended system information, including kernel name/version, hardware architecture, hostname, and OS.

uname -r

This will print only the kernel release number. The uname command shows details about your Linux system’s core components.

70. hostname – Show Or Set The System’s Host Name

The hostname command prints or sets the hostname identifier for your Linux system on the network. With no arguments it displays the current hostname. Passing a name will update the hostname.

For example:

hostname

linuxserver

This prints linuxserver — the configured system hostname.

hostname UbuntuServer

hostnames identify systems on a network. hostname gets or configures the identifying name of your system on the network. The second command helps you change the local hostname to UbuntuServer.

71. uptime – How Long The System Has Been Running

The uptime command shows how long the Linux system has been running since it was last rebooted. It prints the uptime and current time.

Simply run the following command to get your system uptime data:

uptime

23:51:26 up 2 days, 4:12, 1 user, load average: 0.00, 0.01, 0.05

This prints the system uptime showing how long the system has been on since last boot.

72. whoami – Print Active User ID

The whoami command prints the effective username of the current user logged into the system. It displays the privilege level you are operating at.

Type the command in your terminal to get the ID:

whoami

john

This prints the effective username that the current user is logged in and operating as and is useful in scripts or diagnostics to identify what user account actions are being performed as.

74. lscpu – Display CPU Architecture Information

The lscpu command shows detailed CPU architecture information, including:

Number of CPU cores

Number of sockets

Model name

Cache sizes

CPU frequency

Address sizes.

75. lsblk – List Block Devices

The lsblk command lists information about all available block devices, including local disks, partitions, and logical volumes. The output includes device names, labels, sizes, and mount points.

lsblk.

System Administration Commands

System admin commands help you run programs as other users, shut down or reboot the system, and manage init systems and services.

78. sudo – Execute A Command As Another User

The sudo command allows you to run commands as another user, typically the superuser. After entering the sudo order, it will prompt you for your password to authenticate.

This provides elevated access for tasks like installing packages, editing system files, administering services etc.

For example:

sudo adduser bob

[sudo] password for john:

User ‘bob’ has been added to the system.

This uses sudo to create a new user, ‘bob’. Regular users typically cannot add users without sudo.

79. su – Change User ID Or Become Superuser

The su command allows you to switch to another user account including the superuser. You must provide the target user’s password to authenticate. This gives direct access to run commands in another user’s environment.

For example:

su bob

Password:

bob@linux:~$

After inputting bob’s password, this command switches the current user to the user ‘bob’. The shell prompt will reflect the new user.

80. shutdown – Shutdown Or Restart Linux

The shutdown command schedules a system power off, halt or reboot after a specified timer or immediately. It’s required to reboot or shutdown multi-user Linux systems safely.

For example:

shutdown -r now

Broadcast message from root@linux Fri 2023-01-20 18:12:37 CST:

The system is going down for reboot NOW!

This reboots the system instantly with a warning to users.

81. reboot – Reboot Or Restart System

The reboot command restarts the Linux operating system, logging all users off and safely rebooting the system. It synchronizes disks and brings the system down cleanly before restarting.

For example:

reboot

Restarting system.

This immediately reboots the OS. reboot is a simple alternative to shutdown -r.

82. systemctl – Control The systemd System And Service Manager

The systemctl command allows you to manage systemd services like starting, stopping, restarting, or reloading them. Systemd is the new init system used in most modern Linux distros, replacing SysV init.

For example:

systemctl start apache2

==== AUTHENTICATING FOR org.freedesktop.systemd1.manage-units ===

Authentication is required to start 'apache2.service'.

Authenticating as: User Name

Password:

==== AUTHENTICATION COMPLETE ===

This starts the apache2 service after authenticating.

83. service – Run A System V Init Script

The service command runs System V init scripts for controlling services. This allows starting, stopping, restarting, and reloading services managed under traditional SysV init.

For example:

service iptables start

[ ok ] Starting iptables (via systemctl): iptables.service.

The above command starts the iptables firewall service using its SysV init script.

=============================================================

mount – Mount or “attach” drives to the system.

umount – Umount or “remove” drives from the system.

alias – Create shortcuts for long or complex commands.

jobs – List programs currently running jobs in the background.

bg – Resume a stopped or paused background process.

killall – Terminate processes by program name rather than PID.

history – Display previously used commands within the current terminal session.

man – Access help manuals for commands right within the terminal.

ssh – Establish secure encrypted connections to remote servers.

tcpdump – Capture network traffic based on specific criteria