1.cat-Sends file contents to standard output. This is a way to list the contents of short files to the screen. It works well with piping.
cd.. -Move to the parent directory of the current directory. This command will make the current working directory "/home.
5.df-Show the amount of disk space used on each mounted filesystem.
6.less-Similar to the more command, but the user can page up and down through the file.
7.ln-Creates a symbolic link to a file.
8.locate-A fast database driven file locator.
9.logout-Logs the current user off the system.
10.ls-Short listing of directory contents
11.more-Allows file contents or piped output to be sent to the screen one page at a time.
12.mv-Move or rename files
13.pwd-Show the name of the current working directory
14.shutdown-Shuts the system down.
15.whereis-Show where the binary, source and manual page files are for a command
16.rmdir - Remove an existing directory
17.chown - change file owner and group
18.chmod - change file access permissions
19.clear - Clears the terminal screen.
20.mkdir - make directories