Useful Linux Command Line Stuff

Networking

Get the IP address of all interfaces

• networkctl status

Display all IP addresses of the host

• hostname -I

• Enable/disable interface - ip link set <interface> up
• ip link set <interface> down
• Manage firewall rules
  • enable firewall: sudo ufw enable
  • list rules: sudo ufw status
  • allow port: sudo ufw allow <port>
  • deny port: sudo ufw deny <port>
• Connect remotely through SSH
  • ssh <user>@<host IP>

Packages Search for packages apt search <string> snap find <string> List available updates apt list --upgradable Apply all available updates sudo apt update && sudo apt upgrade Install from the Ubuntu archive: sudo apt install <package> Install from the snap store: sudo snap install <package> Which package provides this file? sudo apt install apt-file sudo apt-file update apt-file <filename or command>

Files List files ls List files with permissions and dates ls -al Common file operations create empty: touch <filename> create with content: echo "<content>" > <filename> append content: echo "<content>" >> <filename> display a text file: cat <file> copy: cp <file> <target filename> move/rename: mv <file> <target directory/filename> delete: rm <file> Create a directory mkdir <directory> Create directories recursively mkdir -p <directory1>/<directory2> Delete a directory recursively rm -r <directory> Quick file search locate Search string in file grep <string> <filename> Search string recursively in directory grep -Iris <string> <directory> Find files modified in the last n minutes find <directory> -mmin -<n> -type f eg. find . -mmin -5 -type f Show only the nth column col<n> “<separator>” <filename> eg. col2 “,” foo.csv Display file paginated less <filename> Display first n lines head -n <n> <filename> Display last n lines tail -n <n> <filename> Follow file content as it increases tail -f <filename> Pack a directory into an archive zip: zip -r <target> <source dir> tar.gz: tar cvzf <target>.tar.gz <source dir> Unpack an archive zip: unzip <zip file> tar.gz: tar xf <tar.gz file> Copy file to remote server scp <filename> <user@server>:<destination> eg. scp config.yaml admin@192.0.0.0:/config Copy directory recursively from remote server scp -r <user@server>:<source> <destination> eg. scp -r admin@192.0.0.0:/config /tmp

Security Show which users are logged in w Get password expiration date for <user> chage -l <user> Set password expiration date for <user> sudo chage <user> Lock a user account sudo passwd -l <user> Unlock a user account sudo passwd -u <user> List open ports and associated processes sudo netstat -tulpn

Automatically detect and ban abusive IP addresses sudo apt install fail2ban Show banned IP addresses sudo fail2ban-client status sudo fail2ban-client status <jail> Get the support status for installed packages ubuntu-support-status Enable kernel live patching sudo snap install canonical-livepatch sudo canonical-livepatch enable <token> Visit ubuntu.com/livepatch to get a free token for up to 3 machines.