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Linux - Commands to Know

Last verified: October 2026 against the current man pages (tar, touch, useradd, userdel, groupadd, groupdel) for RHEL / Rocky Linux.

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

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