# Linux - Commands to Know

<p class="callout info">Last verified: October 2026 against the current man pages (tar, touch, useradd, userdel, groupadd, groupdel) for RHEL / Rocky Linux.</p>

This is a quick version of commands to be aware of.

#### System information 

`uname -a` : Displays all system information.

`hostnamectl` : Shows current hostname and related details.

`lscpu` : Lists CPU architecture information.

`timedatectl status` : Shows system time.

#### System monitoring and management

`top` : Displays real-time system processes.

`htop` : An interactive process viewer (needs installation; on RHEL / Rocky Linux it comes from the EPEL repository).

`df -h` : Shows disk usage in a human-readable format.

`free -m` : Displays free and used memory in MB.

`kill [PID]` : Terminates a process (sends SIGTERM by default).

#### Running commands 

`<command> &` : Runs command in the background.

`jobs` : Displays background commands.

`fg %1` : Brings background job 1 (number from jobs) to the foreground.

#### Service management

`sudo systemctl start [service]` : Starts a service.

`sudo systemctl stop [service]` : Stops a service

`sudo systemctl status [service]` : Checks the status of a service.

`sudo systemctl reload [service]` : Reloads a service’s configuration without interrupting its operation.

`journalctl -f` : Follows the journal, showing new log messages in real time.

`journalctl -u [unit]` : Displays logs for a specific systemd unit.

#### Cron jobs and scheduling

`crontab -e` : Edits cron jobs for the current user.

`crontab -l` : Lists cron jobs for the current user.

#### File management

`ls` : Lists files and directories.

`touch` : Creates an empty file, or updates the access and modification times of an existing file.

`cp` : Copies files from source to destination.

`mv` : Moves files or renames them.

`rm` : Deletes a file.

#### Directory navigation

`pwd` : Displays the current directory path.

`cd` : Changes the current directory.

`mkdir` : Creates a new directory.

#### File permissions and ownership

`chmod [who][+/-][permissions]` : Changes file permissions.

`chmod u+x` : Makes a file executable by its owner.

`chown [user]:[group] [file]` : Changes file owner and group.

#### Searching and finding

`find [directory] -name` : Finds files and directories.

`grep` : Searches for a pattern in files.

#### Archiving and compression

`tar -czvf [archive].tar.gz [files]` : Compresses files into a tar.gz archive.

`tar -xvf [archive].tar.gz -C [destination]` : Extracts a compressed tar archive into the destination directory.

#### Text editing and processing

`nano` : Opens a file in the Nano text editor.

`cat` : Displays the contents of a file.

`less` : Displays the paginated content of a file.

`head` : Shows the first few lines of a file.

`tail` : Shows the last few lines of a file.

`awk '{print}' [file]` : Prints every line in a file.

#### User management

`w` : Shows which users are logged in.

`sudo useradd [username]` : Creates a new user (Debian / Ubuntu also have the adduser front end).

`sudo userdel [username]` : Deletes a user (add -r to also remove the home directory).

`sudo passwd` : Sets or changes the password for a user.

`su` : Switches user.

`sudo passwd -l` : Locks a user account.

`sudo passwd -u` : Unlocks a user password.

`sudo chage` : Sets user password expiration date.

#### Group management

`id [username]` : Displays user and group IDs.

`groups [username]` : Shows the groups a user belongs to.

`sudo groupadd [group]` : Creates a new group.

`sudo groupdel [group]` : Deletes a group.

#### Sources

- [https://man7.org/linux/man-pages/man1/tar.1.html](https://man7.org/linux/man-pages/man1/tar.1.html)
- [https://man7.org/linux/man-pages/man1/touch.1.html](https://man7.org/linux/man-pages/man1/touch.1.html)
- [https://man7.org/linux/man-pages/man8/useradd.8.html](https://man7.org/linux/man-pages/man8/useradd.8.html)
- [https://man7.org/linux/man-pages/man8/userdel.8.html](https://man7.org/linux/man-pages/man8/userdel.8.html)
- [https://man7.org/linux/man-pages/man8/groupadd.8.html](https://man7.org/linux/man-pages/man8/groupadd.8.html)
- [https://man7.org/linux/man-pages/man8/groupdel.8.html](https://man7.org/linux/man-pages/man8/groupdel.8.html)
- [https://packages.fedoraproject.org/pkgs/htop/htop/](https://packages.fedoraproject.org/pkgs/htop/htop/)