Linux for starters

  

What is ‘ps’ command stands for?

The ps command prints the process status for some or all of the running processes. The  information  given are the process identification number (PID),the amount of time that the process has taken to execute so far etc

What do you mean by File System ?
 File System is a method to store and organize files and directories on disk. A file system can have different formats called file system types. These formats determine how the information is stored as files and directories. 

What is tmpfs File System ?

tmpfs is a common name for a temporary file storage facility on many Unix-like operating systems. 
It is intended to appear as a mounted file system, but stored in volatile memory instead of a persistent storage device.  RAM disk  also appears as a virtual disk drive and hosts a disk file system.

Everything stored in tmpfs is temporary in the sense that no files will be created on the hard drive; however, swap space is used as backing store in case of low memory situations. On reboot, everything in tmpfs will be lost.The memory used by tmpfs grows and shrinks to accommodate the files it contains and can be swapped out to swap space.

What is the command to change user password expiration time?

CHAGE

What is the command used for changing the attributes of any file ?

chattr

What is the command to check ports running/used over local machine ?

netstat -antp

Command used to lock user password

usermod -L username

What is the command to check current  runlevel ?

who -r