Linux CheatSheet for CE3750 Lab

List of Content

• List of Content
• Get started
• Basic Commands
• System Info
• User Management Commands
• CH.08 Processes
• CH.09 Services & Daemons
• CH.10 SSH
• CH.11 Networking
  • Useful NetworkManager Commands
• CH.12 Software Packages
  • Summary of DNF Commands
• CH.13 Manage File Systems
• Other Important Commands and Topics
  • Linux File System
  • Expansion
  • Pattern Matching
  • Quotes in Variables
  • Redirect & Pipelines
  • Environment Variables
  • history
  • special file-permissions & umask
• Extra Tips & Tricks
  • Alias Command to a one of your own
  • Tab Completion
  • Multi-line Commands
• Contribution
• Directory Structure

---

Get started

1. You can read this Cheatsheet from Github directly, or a better way is to clone this repo and open it with Obsidian with these Steps. 1.

   # if you have git installed on your system
   git clone https://github.com/Ahmad-Mtr/Linux-CheatSheet.git 

   2. Open that directory with Obsidian
   3. Enjoy

2. Here are Alternatives to Red Hat's Lab Environment, in which you can use a bash shell to practice all Commands:

   • Github Codespaces (You can also get pro benefits by registering in Github Education Pack)
   • Replit ( by creating a simple C project and using the shell there)
   • Online Linux Terminal
   • Access a local Terminal on Windows via WSL

Note

You can search 'Fireship Linux' on Youtube for practical & concise Content, see this for example.

And Below is a list of common Linux commands with brief descriptions and examples. For more detailed explanations and options, please follow the links to the specific .md files.

---

Basic Commands

0. Commands that are entered at the shell prompt have three basic parts: command options argument example

ls -al myfolder

• Command: name of executable to run, ls.
• Options: adjust the behavior of the command (normally starts with dashes like -l), -al.
• arguments: target of the command, myfolder.

# You can use comments like other langs by using the `#`
echo "Hello World" # echo = print

mkdir test  # make directory/folder 'test'
cp src dest  # copy src to dest
rm -rf test # remove recusively & forcefully 'test' and its children

STR="Hello CS416 Students!" # This creates a variable named STR
echo $STR  # Hello ...

1. ls - List files and directories.

   ls  # list files and directories in the current location

   For extra details, visit ls.md.

2. cd - Change directory.

   cd /path/to/directory  # change to the specified directory

   For extra details, visit cd.md.

3. pwd - Print working directory.

   pwd  # display the current directory path

4. mkdir - Create a new directory.

   mkdir new_directory  # create a new directory named 'new_directory'

5. rmdir - Remove an empty directory.

   rmdir old_directory  # remove the empty directory 'old_directory'

6. touch - Create an empty file or update the timestamp of an existing file.

   touch newfile.txt  # create a new empty file named 'newfile.txt'

7. rm - Remove files or directories.

   rm file.txt  # remove the file named 'file.txt'

   For extra details, visit rm.md.

8. cp - Copy files or directories.

   cp source.txt destination.txt  # copy 'source.txt' to 'destination.txt'

   For extra details, visit cp.md.

9. mv - Move or rename files and directories.

   mv oldname.txt newname.txt  # rename 'oldname.txt' to 'newname.txt'

   For extra details, visit mv.md.

10. cat - Concatenate and display file contents.

    cat file.txt  # display the contents of 'file.txt'

11. echo - Display a line of text.

    echo "Hello, World!"  # print 'Hello, World!' to the terminal

12. head - Output the first part of files.

    head file.txt  # display the first 10 lines of 'file.txt'

    For extra details, visit head.md.

13. tail - Output the last part of files.

    tail file.txt  # display the last 10 lines of 'file.txt'

    For extra details, visit tail.md.

14. less - View file contents interactively.

    less file.txt  # view 'file.txt' in interactive mode

15. more - View file contents one page at a time.

    more file.txt  # view 'file.txt' one page at a time

16. find - Search for files in a directory hierarchy.

    find /path -name "filename"  # find 'filename' within '/path'

    For extra details, visit find.md.

17. grep - Search text using patterns.

    grep "pattern" file.txt  # search for 'pattern' in 'file.txt'

    For extra details, visit grep.md.

18. chmod - Change file permissions.

    chmod 755 script.sh  # set execute permissions for 'script.sh'

    For extra details, visit chmod.md.

19. chown - Change file owner and group.

    chown user:group file.txt  # change owner and group of 'file.txt'

    For extra details, visit chown.md.

20. man - Display the manual page for a command.

    man ls  # show the manual page for the 'ls' command

    For extra details, visit man.md.

21. wc - Print newline, word, and byte counts for each file.

    wc file.txt  # display line, word, and byte count of 'file.txt'

    For extra details, visit wc.md.

22. date - Display or set the system date and time.

    date  # display the current system date and time

    For extra details, visit date.md.

23. file - Determine file type.

    file file.txt  # determine the type of 'file.txt'

    For extra details, visit file.md.

24. ln - Create links between files.

    ln source.txt link.txt  # create a hard link named 'link.txt' to 'source.txt'

    For extra details, visit ln.md.

---

System Info

26. top - Interactive process viewer.

    top
    htop  # interactive system monitor with more features than 'top' (requires installation)

27. ps - Report a snapshot of current processes.

    ps aux  # list all running processes with detailed information

    For extra details, visit ps.md.

28. kill - Terminate processes.

    kill PID  # terminate the process with specified PID

    For extra details, visit kill.md.

29. uptime - Show how long the system has been running.

    uptime  # display system uptime and load average

30. who & whoami - Show who is logged into the system.

    who  # list users currently logged in
    whoami  # list currentusrer

31. sort - Sort lines of text files.

    sort file.txt  # sort lines in 'file.txt'

32. uniq - Report or omit repeated lines.

    uniq sorted.txt  # remove duplicate lines in 'sorted.txt'

---

User Management Commands

0. id - to display an ID of a User, group.

   id

   For extra details, visit id.md.

1. useradd - Create a new user account.

   useradd newuser  # create a user named 'newuser'

   For extra details, visit useradd.md.

2. usermod - Modify a user account.

   usermod -aG groupname username  # add 'username' to 'groupname'

   For extra details, visit usermod.md.

3. userdel - Delete a user account.

   userdel username  # delete the user 'username'

   For extra details, visit userdel.md.

4. passwd - Change a user password.

   passwd username  # change password for 'username'

   For extra details, visit passwd.md.

5. groupadd - Create a new group.

   groupadd groupname  # create a group named 'groupname'

   For extra details, visit groupadd.md.

6. groupdel - Delete a group.

   groupdel groupname  # delete the group named 'groupname'

   For extra details, visit groupdel.md.

7. groups - Show group memberships.

   groups username  # display groups 'username' belongs to

8. For extra details, visit other Commons.md

---

CH.08 Processes

Command	Explanation
ps	Displays information about the currently running processes.
ps aux	Displays a detailed list of all running processes, including those owned by other users.
top	Displays a dynamic real-time view of the running processes. You can sort the processes by various metrics (e.g., CPU usage, memory usage) by pressing the corresponding sort key.
tail -f	Continuously displays the last few lines of a file as new data is added to it, useful for monitoring log files.
jobs	Lists the jobs currently running in the background.
fg %<job_number>	Brings a background job to the foreground. For example, fg 1 would bring the first background job to the foreground.
Ctrl+C	Terminates the currently running process.
Ctrl+Z	Suspends the currently running process and puts it in the background.
lscpu -p	Displays CPU information in a CSV (comma-separated value) format, which can be useful for scripting.
kill <pid>	Terminates the process with the specified process ID (PID). Examples: kill 1234, kill -9 1234 (force kill).
pkill <process_name>	Terminates all processes with the specified name. Examples: pkill firefox, pkill -u username.

Here are some additional details:

top:

• Press M to sort by memory usage, P to sort by CPU usage, N to sort by PID, etc.
• Press k to kill a process, r to renice (change priority of) a process.

kill:

• kill -l lists all available signal names that can be sent to a process.
• kill -9 <pid> sends the SIGKILL signal, which is a "hard" kill and cannot be ignored by the process.
• kill -15 <pid> sends the SIGTERM signal, which is a "soft" kill and allows the process to clean up and exit gracefully.

pkill:

• pkill firefox kills all processes named "firefox".
• pkill -u username kills all processes owned by the specified user.
• pkill -signal name sends the specified signal to matching processes.

---

CH.09 Services & Daemons

Here's the markdown table with the requested commands related to services and daemons:

Command	Explanation
systemctl	The central management tool for controlling the systemd init system.
systemctl list-units --type=service	Lists all installed service units on the system.
systemctl list-units --type=path	Lists all path units (both active and inactive).
systemctl list-units --type=service | grep -i login	Lists all service units related to the login process.
systemctl status systemd-logind.service	Displays the status of the systemd-logind service.
systemctl disable <service_name>	Configures a service not to start at system boot.
systemctl stop <service_name>	Stops a running service.
systemctl status <service_name>	Verifies if the service has stopped.
systemctl list-dependencies <service_name>	Lists the dependencies of a given service.
systemctl mask <service_name>	Masks a service, preventing it from being started.
systemctl status <masked_service>	Checks the status of a masked service.

Additional details:

• systemctl list-units --type=service: This command lists all installed service units on the system, providing information such as the unit name, load state, active state, and unit file state.

• systemctl disable <service_name>: This command configures the specified service not to start automatically at system boot. The service can still be started manually using systemctl start <service_name>.

• systemctl stop <service_name> and systemctl status <service_name>: These commands stop a running service and verify if the service has indeed stopped, respectively.

• systemctl list-dependencies <service_name>: This command displays the dependencies of the specified service, which can be useful for understanding the service's relationships with other system components.

• systemctl mask <service_name>: This command masks the specified service, which means that the service cannot be started, restarted, or stopped. The service is effectively disabled and hidden from the system.

---

CH.10 SSH

Command	Explanation
ssh Admin_A@servera	Connect to the server "servera" using the "Admin_A" user account.
ssh-keygen	Generate a new RSA SSH key pair When prompted, enter the wanted passphrase.
ssh-copy-id Admin_A@servera	Copy the generated public key to the "servera" server for the "Admin_A" user.
eval "$(ssh-agent -s)"	Start the ssh-agent program manually.
ssh-add ~/.ssh/key-pass	Add the private key from the ~/.ssh/key-pass file to the ssh-agent.
systemctl reload sshd	Reload the SSH daemon to apply the configuration changes.

This table covers the steps you requested:

1. Connect to "servera" via SSH using the "Admin_A" user account.
2. Generate a new SSH key pair with the "ReDHat" passphrase.
3. Copy the public key to the "servera" server for the "Admin_A" user.
4. Start the ssh-agent program manually.
5. Add the private key from the ~/.ssh/key-pass file to the ssh-agent.
6. Reload the SSH daemon to apply the configuration changes.

---

CH.11 Networking

Command	Purpose
ip addr show	Display detailed information about all network interfaces and their IP addresses.
ping <host>	Send ICMP echo requests to a host to test connectivity and measure round-trip time.
ping6 <host>	Send ICMPv6 echo requests to a host for testing IPv6 connectivity.
ping -c <count> <host>	Send a specified number of ICMP echo requests to a host.
ip -br addr show	Show brief information about all network interfaces and their IP addresses.
ip link show	Display details about network interfaces, including their state and MAC addresses.
ip route	Show the routing table for IPv4.
ip -6 route	Show the routing table for IPv6.
tracepath <host>	Trace the network path to a destination, showing each hop with RTT.
traceroute <host>	Trace the route packets take to a destination, showing each hop and delay.
ss	Display active sockets and their connections, similar to netstat.

Useful NetworkManager Commands

Command	Purpose
nmcli dev status	Show the NetworkManager status of all network interfaces.
nmcli con show	List all connections.
nmcli con show <name>	List the current settings for the connection name.
nmcli con add con-name <name>	Add and name a new connection profile.
nmcli con mod <name>	Modify the connection name.
nmcli con reload	Reload the configuration files, after manual file editing.
nmcli con up <name>	Activate the connection name.
nmcli dev dis <dev>	Disconnect the interface, which also deactivates the current connection.
nmcli con del <name>	Delete the specified connection and its configuration file.

---

CH.12 Software Packages

Command	Explanation
rpm -qa	Lists all installed RPM packages on the system.
rpm -qa | grep X	Searches for installed RPM packages that contain the string "X" in their name.
rpm -qf <file_path>	Identifies the RPM package that owns the specified file or file path.
rpm -q <package_name>	Retrieves information about a specific installed package.
rpm -qi <package_name>	Displays detailed information about the specified installed package.
rpm -ql <package_name>	Lists all files owned by the specified installed package.
rpm -qc <package_name>	Lists the configuration files owned by the specified installed package.
rpm -qd <package_name>	Lists the documentation files owned by the specified installed package.
rpm -q --scripts <package_name>	Displays the pre- and post-installation and uninstallation scripts for the specified package.
rpm -qlp <package_file.rpm>	Lists all files owned by the specified RPM package file (not installed).
rpm -q <package_name>	Retrieves information about a specific installed package.
rpm -ivh <package_file.rpm>	Installs the specified RPM package file.
rpm2cpio <package_name>.rpm | cpio -id	Extract Package content to your $home directory.

Summary of DNF Commands

Command:	Task:
dnf list [NAME-PATTERN]	List installed and available packages by name.
dnf group list	List installed and available groups.
dnf search KEYWORD	Search for a package by keyword.
dnf info PACKAGENAME	Show details of a package.
dnf install PACKAGENAME	Install a package.
dnf group install GROUPNAME	Install a package group.
dnf update	Update all packages.
dnf remove PACKAGENAME	Remove a package.
dnf history	Display transaction history.
dnf repolist all	List all available repos and their statuses on systems.

---

CH.13 Manage File Systems

Command	Explanation
df	Displays the available disk space and usage on the file system.
df -h	Displays the available disk space and usage in a human-readable format (e.g., GB, MB).
du	Estimates the file space usage for a directory or file.
lsblk	Lists information about all available block devices.
lsblk -fp	Lists information about all available block devices in a tree-like format.
mount	Mounts a file system. Examples: mount /dev/sda1 /mnt, mount -t ext4 /dev/sda1 /mnt
umount	Unmounts a file system. Example: umount /mnt
lsof	Lists open files and the processes that opened them.
locate	Searches for files by name.
locate -i <filename>	Searches for files by name, ignoring case.
locate -n 5 <filename>	Limits the output to the first 5 matching files.
find	Searches for files based on various criteria.
find . -iname '*.txt'	Finds all files with a .txt extension (case-insensitive).
find . -user <username>	Finds all files owned by the specified user.
find . -group <groupname>	Finds all files owned by the specified group.
find . -uid <uid>	Finds all files owned by the specified user ID.
find . -gid <gid>	Finds all files owned by the specified group ID.
find / -perm /644 or find . -perm -644	Finds all files with at least 644 permissions.
find . -ls	Finds all files and displays detailed information about them.
find . -size +1G	Finds all files larger than 1 GB.
find . -size -100M	Finds all files smaller than 100 MB.
find . -size +100M -size -1G	Finds all files between 100 MB and 1 GB.
find / -mmin 120	find Files that changed 120 minutes ago.
find / -mmin +120	find Files that changed more than 120 minutes ago.
find / -mmin -120	find Files that changed less than 120 minutes ago.
find . -type f	Finds all regular files. use d for directories, l for softlinks, and b for block-devices
find . -type d	Finds all directories.

---

Other Important Commands and Topics

Linux File System

How Directories in Linux are structured, watching this short video is highly recommended. Anyways, more For extra details, visit file-system.md.

Expansion

Shell expansion allows you to use variables, wildcards, and other features in commands. sh echo {1..5} # generates a sequence: 1 2 3 4 5 For extra details, visit expansion.md.

Pattern Matching

Matching file and directory names using patterns. sh ls *.txt # list all '.txt' files in the directory For extra details, visit pattern-matching.md.

Quotes in Variables

• Double quotes " allow variable resolution or referencing.

name="Ahmad"
greeting="Hello, $name!"
echo "$greeting" # Hello, Ahmad!

• Single quotes ' do not allow variable resolution.

name="Ahmad"
greeting='Hello, $name!' # Notice the double quotes
echo "$greeting" # Hello, $name!

Redirect & Pipelines

Redirect input and output, and use pipelines to connect commands. sh ls > files.txt # redirect output of 'ls' to 'files.txt' sh cat file.txt | grep "pattern" # use a pipeline to search 'pattern' in 'file.txt' For extra details, visit redirect-pipelines.md.

Environment Variables

Variables that affect the way processes run on your system. sh echo $PATH # display the current PATH environment variable For extra details, visit environment-variables.md.

history

Display or manipulate the command history. sh history # show the command history For extra details, visit history.md.

special file-permissions & umask

For extra details, visit Special File Permissions & umask.md

---

Extra Tips & Tricks

Alias Command to a one of your own

• instead of creating files common way; using touch, you can alias it to a one of your own:

1. Open ~/.bashrc (or ~/.bash_profile if not there) in your editor, using vim for example.
2. add this to the User Aliases section(usually last one)

Alias batata='touch'

3. Source it using source ~/.bashrc
4. use batata file.c to create Files instead of touch

Common aliases include: ls to dir, sudo to plz Explanation: Since those Commands are executable binaries, you can can create a Command that aliases/points to an existing Command (which is touch in this case)

Tab Completion

Tab Completion is a powerful feature that makes navigating the command line faster and more efficient by automatically completing partially typed commands or filenames. Here's how you can use it:

• Complete Commands: Start typing a command and press the Tab key to auto-complete it. If there are multiple possibilities, pressing Tab twice will show a list of available commands.

  `ls Docu[TAB]    # Autocomplete 'Documents' if it exists`

Multi-line Commands

In Linux, you can write multi-line commands for better readability or when executing complex scripts. This is particularly useful in shell scripting or when entering commands with long arguments.

• Using Backslash (\): The backslash at the end of a line allows continuation on the next line.

echo "This is a \ multi-line \ command."

Contribution

The Cheatsheet follows a consistent Format, take the ls command as an example, You'll find a general use-case & explanation for the Command on this Page, but for extra details, Options and Others, you'll find a seperate File for this Command if needed. Example:

• README.md

ls # list Files & Direcctories on this place

For extra details visit ls.md

• ls.md Options include:
  • -h for more human readable style.
  • ...etc. You can use it to list the Root Directory in a Human-readable format:

ls -h /

---

Directory Structure

using tree command btw.

├───.obsidian
│   └───themes
│       └───Catppuccin
├───assets
├───basic-commands
├───Labs
├───others
├───permissions
├───system-info
└───user-management