If the monitor option of the set command is turned on, an interactive shell associates a job with each pipeline. It keeps a table of current jobs, printed by the jobs command, and assigns them small integer numbers. When a job is started asynchronously with &, the shell prints a line which looks like:
indicating that the job which was started asynchronously was job number 1 and had one (top-level) process, whose process id was 1234.
This paragraph and the next require features that are not in all versions of the Unix operating system and may not apply. If you are running a job and wish to do something else you may hit the key ^Z (control-Z) which sends a STOP signal to the current job. The shell will then normally indicate that ...