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 
 
 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/man8/useradd.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/groupdel.8.html 
 https://packages.fedoraproject.org/pkgs/htop/htop/