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<a name="Jobs-_0026-Signals-1"></a>
<h1 class="chapter">10. Jobs & Signals</h1>
<hr size="6">
<a name="Jobs"></a>
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<h2 class="section">10.1 Jobs</h2>
<a name="index-jobs"></a>
<a name="index-MONITOR_002c-use-of"></a>
<p>If the <tt>MONITOR</tt> option is set,
an interactive shell associates a <em>job</em> with each pipeline.
It keeps a table of current jobs, printed by the <tt>jobs</tt>
command, and assigns them small integer numbers.
When a job is started asynchronously with ‘<tt>&</tt>’,
the shell prints a line to standard error which looks like:
</p>
<table><tr><td> </td><td><pre class="example">[1] 1234
</pre></td></tr></table>
<p>indicating that the job which was started asynchronously was job number
1 and had one (top-level) process, whose process ID was 1234.
</p>
<p>If a job is started with ‘<tt>&|</tt>’ or ‘<tt>&!</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.
</p>
<p>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</tt> signal to the current job: this key
may be redefined by the <tt>susp</tt> option of the external <tt>stty</tt> command.
<a name="index-jobs_002c-suspending"></a>
<a name="index-suspending-jobs"></a>
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,
<a name="index-bg_002c-use-of"></a>
putting it in the background with the <tt>bg</tt> command, or run some other
commands and then eventually bring the job back into the foreground with
<a name="index-fg_002c-use-of"></a>
the foreground command <tt>fg</tt>. A ^Z takes effect immediately and
is like an interrupt in that pending output and unread input are discarded
when it is typed.
</p>
<p>A job being run in the background will suspend if it tries to read
from the terminal.
<a name="index-background-jobs_002c-I_002fO"></a>
<a name="index-jobs_002c-background_002c-I_002fO"></a>
Background jobs are normally allowed to produce output,
but this can be disabled by giving the command ‘<tt>stty tostop</tt>’.
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.
</p>
<p>When a command is suspended and continued later with the <tt>fg</tt> or
<tt>wait</tt> builtins, zsh restores tty modes that were in effect when it was
suspended. This (intentionally) does not apply if the command is
continued via ‘<tt>kill -CONT</tt>’, nor when it is continued with <tt>bg</tt>.
</p>
<a name="index-jobs_002c-referring-to"></a>
<a name="index-referring-to-jobs"></a>
<p>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:
</p>
<dl compact="compact">
<dt> <tt>%</tt><var>number</var></dt>
<dd><p>The job with the given number.
</p></dd>
<dt> <tt>%</tt><var>string</var></dt>
<dd><p>Any job whose command line begins with <var>string</var>.
</p></dd>
<dt> <tt>%?</tt><var>string</var></dt>
<dd><p>Any job whose command line contains <var>string</var>.
</p></dd>
<dt> <tt>%%</tt></dt>
<dd><p>Current job.
</p></dd>
<dt> <tt>%+</tt></dt>
<dd><p>Equivalent to ‘<tt>%%</tt>’.
</p></dd>
<dt> <tt>%-</tt></dt>
<dd><p>Previous job.
</p></dd>
</dl>
<p>The shell learns immediately whenever a process changes state.
<a name="index-NOTIFY_002c-use-of"></a>
It normally informs you whenever a job becomes blocked so that
no further progress is possible. If the <tt>NOTIFY</tt> option is not set,
it waits until just before it prints a prompt before it informs you.
All such notifications are sent directly to the terminal, not to
the standard output or standard error.
</p>
<p>When the monitor mode is on, each background job that completes
triggers any trap set for <tt>CHLD</tt>.
</p>
<p>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</tt> 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</tt> signal, if the <tt>HUP</tt> option is set.
<a name="index-HUP_002c-use-of"></a>
</p>
<a name="index-jobs_002c-disowning"></a>
<a name="index-disowning-jobs"></a>
<a name="index-disown_002c-use-of"></a>
<p>To avoid having the shell terminate the running jobs, either
use the <cite>nohup</cite> command (see man page nohup(1))
or the <tt>disown</tt> builtin.
</p>
<hr size="6">
<a name="Signals"></a>
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<h2 class="section">10.2 Signals</h2>
<p>The <tt>INT</tt> and <tt>QUIT</tt> signals for an invoked
command are ignored if the command is followed by
‘<tt>&</tt>’ and the <tt>MONITOR</tt> option is not active.
The shell itself always ignores the <tt>QUIT</tt> signal.
Otherwise, signals have the values
inherited by the shell from its parent
(but see the <tt>TRAP</tt><var>NAL</var> special functions in <a href="Functions.html#Functions">Functions</a>).
</p><hr size="6">
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