texinode(Jobs & Signals)(Arithmetic Evaluation)(Functions)(Top)
chapter(Jobs & Signals)
sect(Jobs)
cindex(jobs)
If the tt(MONITOR) option is set,
an interactive shell associates a em(job) with each pipeline.
It keeps a table of current jobs, printed by the tt(jobs)
command, and assigns them small integer numbers.
When a job is started asynchronously with `tt(&)',
the shell prints a line which looks like:

example([1] 1234)

indicating that the job which was started asynchronously was job number
1 and had one (top-level) process, whose process ID was 1234.

If a job is started with `tt(&|)' or `tt(&!)',
then that job is immediately disowned.  After startup, it
does not have a place in the job table, and is not subject
to the job control features described here.

If you are running a job and wish to do something else you may hit the key
^Z (control-Z) which sends a tt(TSTP) signal to the current job:  this key
may be redefined by the tt(susp) option of the external tt(stty) command.
cindex(jobs, suspending)
cindex(suspending jobs)
The shell will then normally indicate that the job has been `suspended',
and print another prompt.  You can then manipulate the state of this job,
findex(bg, use of)
putting it in the background with the tt(bg) command, or run some other
commands and then eventually bring the job back into the foreground with
findex(fg, use of)
the foreground command tt(fg).  A ^Z takes effect immediately and
is like an interrupt in that pending output and unread input are discarded
when it is typed.

A job being run in the background will suspend if it tries to read
from the terminal.
cindex(background jobs, I/O)
cindex(jobs, background, I/O)
Background jobs are normally allowed to produce output,
but this can be disabled by giving the command `tt(stty tostop)'.
If you set this
tty option, then background jobs will suspend when they try to produce
output like they do when they try to read input.

cindex(jobs, referring to)
cindex(referring to jobs)
There are several ways to refer to jobs in the shell.
A job can be referred to by the process ID of any process of the job
or by one of the following:

startsitem()
sitem(tt(%)var(number))(The job with the given number.)
sitem(tt(%)var(string))(Any job whose command line begins with var(string).)
sitem(tt(%?)var(string))(Any job whose command line contains var(string).)
sitem(tt(%%))(Current job.)
sitem(tt(%PLUS()))(Equivalent to `tt(%%)'.)
sitem(tt(%-))(Previous job.)
endsitem()

The shell learns immediately whenever a process changes state.
pindex(NOTIFY, use of)
It normally informs you whenever a job becomes blocked so that
no further progress is possible.  If the tt(NOTIFY) option is not set,
it waits until just before it prints a prompt before it informs you.

When the monitor mode is on, each background job that completes
triggers any trap set for tt(CHLD).

When you try to leave the shell while jobs are running or suspended, you will
be warned that `You have suspended (running) jobs'.
You may use the tt(jobs) command to see what they are.
If you do this or immediately try to
exit again, the shell will not warn you a second time; the suspended
jobs will be terminated, and the running jobs will be sent
a tt(SIGHUP) signal, if the tt(HUP) option is set.
pindex(HUP, use of)

cindex(jobs, disowning)
cindex(disowning jobs)
findex(disown, use of)
To avoid having the shell terminate the running jobs, either
use the bf(nohup) command (see manref(nohup)(1))
or the tt(disown) builtin.
sect(Signals)
The tt(INT) and tt(QUIT) signals for an invoked
command are ignored if the command is followed by
`tt(&)' and the tt(MONITOR) option is not active.
Otherwise, signals have the values
inherited by the shell from its parent
(but see the tt(TRAP)var(NAL) special functions in noderef(Functions)).
