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| <h3 class="section">27.2 Job Control is Optional</h3> |
| |
| <p><a name="index-job-control-is-optional-3207"></a> |
| Not all operating systems support job control. The GNU system does |
| support job control, but if you are using the GNU library on some other |
| system, that system may not support job control itself. |
| |
| <p>You can use the <code>_POSIX_JOB_CONTROL</code> macro to test at compile-time |
| whether the system supports job control. See <a href="System-Options.html#System-Options">System Options</a>. |
| |
| <p>If job control is not supported, then there can be only one process |
| group per session, which behaves as if it were always in the foreground. |
| The functions for creating additional process groups simply fail with |
| the error code <code>ENOSYS</code>. |
| |
| <p>The macros naming the various job control signals (see <a href="Job-Control-Signals.html#Job-Control-Signals">Job Control Signals</a>) are defined even if job control is not supported. However, |
| the system never generates these signals, and attempts to send a job |
| control signal or examine or specify their actions report errors or do |
| nothing. |
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