What is difference between a job and a process in Unix?

Question

What is the difference between a job and a process in Unix ? Can you please give an example ?

Answer 1

Jobs are processes which are started by a shell. The shell keeps track of these in a job table. The jobs command shows a list of active background processes. They get a jobspec number which is not the pid of the process. Commands like fg use the jobspec id.

In the spirit of Jürgen Hötzel's example:

find $HOME | sort & [1] 15317 $ jobs [1]+  Running                 find $HOME | sort & $ fg find $HOME | sort   C-c C-z [1]+  Stopped                 find $HOME | sort $ bg 1 [1]+ find $HOME | sort & 

Try the examples yourself and look at the man pages.

Answer 2

A Process Group can be considered as a Job. For example you create a background process group in shell:

$ find $HOME|sort & [1] 2668 

And you can see two processes as members of the new process group:

$ ps -p 2668 -o cmd,pgrp  CMD                          PGRP sort                         2667   $ ps -p "$(pgrep -d , -g 2667)" -o cmd,pgrp CMD                          PGRP find /home/juergen           2667 sort                         2667 

You can can also kill the whole process group/job:

$ pkill -g 2667 

Answer 3

http://en.wikipedia.org/wiki/Job_control_%28Unix%29:

Processes under the influence of a job control facility are referred to as jobs.

Answer 4

http://en.wikipedia.org/wiki/Job_control_%28Unix%29

Jobs are one or more processes that are grouped together as a 'job', where job is a UNIX shell concept.