Interview Questions - UNIX Process Management

A daemon is a process that detaches itself from the terminal and runs, disconnected, in the background, waiting for requests and responding to them. It can also be defined as the background process that does not belong to a terminal session. Many system functions are commonly performed by daemons, including the sendmail daemon, which handles mail, and the NNTP daemon, which handles USENET news. Many other daemons may exist.
Some of the most common daemons are:

1. init: Takes over the basic running of the system when the kernel has finished the boot process.
2. inetd: Responsible for starting network services that do not have their own stand-alone daemons. For example, inetd usually takes care of incoming rlogin, telnet, and ftp connections.
3. cron: Responsible for running repetitive tasks on a regular schedule.

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.

The "kill" command takes the PID as one argument; this identifies which process to terminate. The PID of a process can be got using "ps" command.

The most common reason to put a process in the background is to allow you to do something else interactively without waiting for the process to complete. At the end of the command you add the special background symbol, &. This symbol tells your shell to execute the given command in the background.
Example: cp *.* ../backup&   (cp is for copy)