1)df : It shows the amount of available disk space being used by the files systems.
2)free : It shows the total amount of free and used Physical and swap memory in the system, as well as the buffer used by the kernel.
3)sleep : delay for a specified amount of time.
4)sleep 60 & : It run independently of the terminal, allowing you to perform other task simultaneously.
5)ps : Process status can be used to see/ list all the running process.
6)kill : for process running in background kill command used to terminated the process.
7)top :This command is used to show all the running process with in the working environment of Linux.
8)nice : It starts a new process(job) and assigns it a priority (nice) value at the same time.
9)pwd : print name of current working directory.
10)ls : The ls command is used to list the files and directories in the current directory.
11)cd : The cd command is used to move between folders.
12)mkdir : The mkdir command, an abbreviation for "make directory" allow you to create new folder within your existing file system.
13)rmdir: The rmdir command, short for "remove directory" enable you to delete empty directories.
14)cp: The cp command is used to copy file and directories from one location to another.
15)mv: The mv command is used to move or rename files and directories from one location to another.
16)ping: The ping command is used to ensure that a computer can communicate with a specified device over the network.
17)nslookup: the nslookup is a program to query Internet domain name servers.
18)traceroute: The traceroute command is used to determine the path taken by packets from the source to the destination host. it also shows the number the hops required to reach the destination.
19)host: The host command is used to perform DNS lookup. it can find IP address associated with a domain name.
20)netstat: The netstat(Network Statistics) command displays information about: Network connections, Routing tables, Interface statistics, port status.