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| <h3 class="section">31.2 Overall System Options</h3> |
| |
| <p><a name="index-POSIX-optional-features-3512"></a><a name="index-optional-POSIX-features-3513"></a> |
| POSIX defines certain system-specific options that not all POSIX systems |
| support. Since these options are provided in the kernel, not in the |
| library, simply using the GNU C library does not guarantee any of these |
| features is supported; it depends on the system you are using. |
| |
| <p><a name="index-unistd_002eh-3514"></a>You can test for the availability of a given option using the macros in |
| this section, together with the function <code>sysconf</code>. The macros are |
| defined only if you include <samp><span class="file">unistd.h</span></samp>. |
| |
| <p>For the following macros, if the macro is defined in <samp><span class="file">unistd.h</span></samp>, |
| then the option is supported. Otherwise, the option may or may not be |
| supported; use <code>sysconf</code> to find out. See <a href="Sysconf.html#Sysconf">Sysconf</a>. |
| |
| <!-- unistd.h --> |
| <!-- POSIX.1 --> |
| <div class="defun"> |
| — Macro: int <b>_POSIX_JOB_CONTROL</b><var><a name="index-g_t_005fPOSIX_005fJOB_005fCONTROL-3515"></a></var><br> |
| <blockquote><p>If this symbol is defined, it indicates that the system supports job |
| control. Otherwise, the implementation behaves as if all processes |
| within a session belong to a single process group. See <a href="Job-Control.html#Job-Control">Job Control</a>. |
| </p></blockquote></div> |
| |
| <!-- unistd.h --> |
| <!-- POSIX.1 --> |
| <div class="defun"> |
| — Macro: int <b>_POSIX_SAVED_IDS</b><var><a name="index-g_t_005fPOSIX_005fSAVED_005fIDS-3516"></a></var><br> |
| <blockquote><p>If this symbol is defined, it indicates that the system remembers the |
| effective user and group IDs of a process before it executes an |
| executable file with the set-user-ID or set-group-ID bits set, and that |
| explicitly changing the effective user or group IDs back to these values |
| is permitted. If this option is not defined, then if a nonprivileged |
| process changes its effective user or group ID to the real user or group |
| ID of the process, it can't change it back again. See <a href="Enable_002fDisable-Setuid.html#Enable_002fDisable-Setuid">Enable/Disable Setuid</a>. |
| </p></blockquote></div> |
| |
| <p>For the following macros, if the macro is defined in <samp><span class="file">unistd.h</span></samp>, |
| then its value indicates whether the option is supported. A value of |
| <code>-1</code> means no, and any other value means yes. If the macro is not |
| defined, then the option may or may not be supported; use <code>sysconf</code> |
| to find out. See <a href="Sysconf.html#Sysconf">Sysconf</a>. |
| |
| <!-- unistd.h --> |
| <!-- POSIX.2 --> |
| <div class="defun"> |
| — Macro: int <b>_POSIX2_C_DEV</b><var><a name="index-g_t_005fPOSIX2_005fC_005fDEV-3517"></a></var><br> |
| <blockquote><p>If this symbol is defined, it indicates that the system has the POSIX.2 |
| C compiler command, <code>c89</code>. The GNU C library always defines this |
| as <code>1</code>, on the assumption that you would not have installed it if |
| you didn't have a C compiler. |
| </p></blockquote></div> |
| |
| <!-- unistd.h --> |
| <!-- POSIX.2 --> |
| <div class="defun"> |
| — Macro: int <b>_POSIX2_FORT_DEV</b><var><a name="index-g_t_005fPOSIX2_005fFORT_005fDEV-3518"></a></var><br> |
| <blockquote><p>If this symbol is defined, it indicates that the system has the POSIX.2 |
| Fortran compiler command, <code>fort77</code>. The GNU C library never |
| defines this, because we don't know what the system has. |
| </p></blockquote></div> |
| |
| <!-- unistd.h --> |
| <!-- POSIX.2 --> |
| <div class="defun"> |
| — Macro: int <b>_POSIX2_FORT_RUN</b><var><a name="index-g_t_005fPOSIX2_005fFORT_005fRUN-3519"></a></var><br> |
| <blockquote><p>If this symbol is defined, it indicates that the system has the POSIX.2 |
| <code>asa</code> command to interpret Fortran carriage control. The GNU C |
| library never defines this, because we don't know what the system has. |
| </p></blockquote></div> |
| |
| <!-- unistd.h --> |
| <!-- POSIX.2 --> |
| <div class="defun"> |
| — Macro: int <b>_POSIX2_LOCALEDEF</b><var><a name="index-g_t_005fPOSIX2_005fLOCALEDEF-3520"></a></var><br> |
| <blockquote><p>If this symbol is defined, it indicates that the system has the POSIX.2 |
| <code>localedef</code> command. The GNU C library never defines this, because |
| we don't know what the system has. |
| </p></blockquote></div> |
| |
| <!-- unistd.h --> |
| <!-- POSIX.2 --> |
| <div class="defun"> |
| — Macro: int <b>_POSIX2_SW_DEV</b><var><a name="index-g_t_005fPOSIX2_005fSW_005fDEV-3521"></a></var><br> |
| <blockquote><p>If this symbol is defined, it indicates that the system has the POSIX.2 |
| commands <code>ar</code>, <code>make</code>, and <code>strip</code>. The GNU C library |
| always defines this as <code>1</code>, on the assumption that you had to have |
| <code>ar</code> and <code>make</code> to install the library, and it's unlikely that |
| <code>strip</code> would be absent when those are present. |
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