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| <h3 class="section">27.4 Access to the Controlling Terminal</h3> |
| |
| <p><a name="index-controlling-terminal_002c-access-to-3209"></a> |
| Processes in the foreground job of a controlling terminal have |
| unrestricted access to that terminal; background processes do not. This |
| section describes in more detail what happens when a process in a |
| background job tries to access its controlling terminal. |
| |
| <p><a name="index-g_t_0040code_007bSIGTTIN_007d_002c-from-background-job-3210"></a>When a process in a background job tries to read from its controlling |
| terminal, the process group is usually sent a <code>SIGTTIN</code> signal. |
| This normally causes all of the processes in that group to stop (unless |
| they handle the signal and don't stop themselves). However, if the |
| reading process is ignoring or blocking this signal, then <code>read</code> |
| fails with an <code>EIO</code> error instead. |
| |
| <p><a name="index-g_t_0040code_007bSIGTTOU_007d_002c-from-background-job-3211"></a>Similarly, when a process in a background job tries to write to its |
| controlling terminal, the default behavior is to send a <code>SIGTTOU</code> |
| signal to the process group. However, the behavior is modified by the |
| <code>TOSTOP</code> bit of the local modes flags (see <a href="Local-Modes.html#Local-Modes">Local Modes</a>). If |
| this bit is not set (which is the default), then writing to the |
| controlling terminal is always permitted without sending a signal. |
| Writing is also permitted if the <code>SIGTTOU</code> signal is being ignored |
| or blocked by the writing process. |
| |
| <p>Most other terminal operations that a program can do are treated as |
| reading or as writing. (The description of each operation should say |
| which.) |
| |
| <p>For more information about the primitive <code>read</code> and <code>write</code> |
| functions, see <a href="I_002fO-Primitives.html#I_002fO-Primitives">I/O Primitives</a>. |
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