linux command

delete directory
rm -rf letters/
Add User 
useradd -u <username> -p <password> -d <directory>
Change Port
vi /etc/ssh/sshd_config
Change Port
vi /etc/ssh/sshd_config
# Run ssh on a non-standard port:
Port 2345  #Change me
service sshd restart
List All User
cat /etc/passwd
Archieve

zip -r filename.zip files

Compress an Entire Directory or a Single File

tar -czvf archive.tar.gz /path/to/directory-or-file
or
tar -czvf archive.tar.gz /home/ubuntu/Downloads /usr/local/stuff /home/ubuntu/Documents/notes.txt

Extract an Archive

tar -xzvf archive.tar.gz

Find / Search File Recursive

find -name *tgz

source : http://www.howtogeek.com/248780/how-to-compress-and-extract-files-using-the-tar-command-on-linux/