# Linux - Commands to Know

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).

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

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

kill : Terminates a process.

#### Running commands <command></command>

&lt;command&gt; &amp; : Runs command in the background.

jobs : Displays background commands.

fg <command></command> : Brings command to the foreground.

#### Service management

sudo systemctl start : Starts a service.

sudo systemctl stop : Stops a service

sudo systemctl status : Checks the status of a service.

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

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

journalctl -u : 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 last accessed date.

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 \[user\]:\[group\] : 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 \[files\] : Compresses files into a tar.gz archive.

tar -xvf \[destination\] : Extracts a compressed tar archive.

#### 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}’ : Prints every line in a file.

#### User management

w : Shows which users are logged in.

sudo adduser : Creates a new user.

sudo deluser : Deletes a user.

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 addgroup : Creates a new group.

sudo delgroup : Deletes a group.