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| <h4 class="subsection">18.2.1 openlog</h4> |
| |
| <p>The symbols referred to in this section are declared in the file |
| <samp><span class="file">syslog.h</span></samp>. |
| |
| <!-- syslog.h --> |
| <!-- BSD --> |
| <div class="defun"> |
| — Function: void <b>openlog</b> (<var>const char *ident, int option, int facility</var>)<var><a name="index-openlog-2034"></a></var><br> |
| <blockquote> |
| <p><code>openlog</code> opens or reopens a connection to Syslog in preparation |
| for submitting messages. |
| |
| <p><var>ident</var> is an arbitrary identification string which future |
| <code>syslog</code> invocations will prefix to each message. This is intended |
| to identify the source of the message, and people conventionally set it |
| to the name of the program that will submit the messages. |
| |
| <p>If <var>ident</var> is NULL, or if <code>openlog</code> is not called, the default |
| identification string used in Syslog messages will be the program name, |
| taken from argv[0]. |
| |
| <p>Please note that the string pointer <var>ident</var> will be retained |
| internally by the Syslog routines. You must not free the memory that |
| <var>ident</var> points to. It is also dangerous to pass a reference to an |
| automatic variable since leaving the scope would mean ending the |
| lifetime of the variable. If you want to change the <var>ident</var> string, |
| you must call <code>openlog</code> again; overwriting the string pointed to by |
| <var>ident</var> is not thread-safe. |
| |
| <p>You can cause the Syslog routines to drop the reference to <var>ident</var> and |
| go back to the default string (the program name taken from argv[0]), by |
| calling <code>closelog</code>: See <a href="closelog.html#closelog">closelog</a>. |
| |
| <p>In particular, if you are writing code for a shared library that might get |
| loaded and then unloaded (e.g. a PAM module), and you use <code>openlog</code>, |
| you must call <code>closelog</code> before any point where your library might |
| get unloaded, as in this example: |
| |
| <pre class="smallexample"> #include <syslog.h> |
| |
| void |
| shared_library_function (void) |
| { |
| openlog ("mylibrary", option, priority); |
| |
| syslog (LOG_INFO, "shared library has been invoked"); |
| |
| closelog (); |
| } |
| </pre> |
| <p>Without the call to <code>closelog</code>, future invocations of <code>syslog</code> |
| by the program using the shared library may crash, if the library gets |
| unloaded and the memory containing the string <code>"mylibrary"</code> becomes |
| unmapped. This is a limitation of the BSD syslog interface. |
| |
| <p><code>openlog</code> may or may not open the <samp><span class="file">/dev/log</span></samp> socket, depending |
| on <var>option</var>. If it does, it tries to open it and connect it as a |
| stream socket. If that doesn't work, it tries to open it and connect it |
| as a datagram socket. The socket has the “Close on Exec” attribute, |
| so the kernel will close it if the process performs an exec. |
| |
| <p>You don't have to use <code>openlog</code>. If you call <code>syslog</code> without |
| having called <code>openlog</code>, <code>syslog</code> just opens the connection |
| implicitly and uses defaults for the information in <var>ident</var> and |
| <var>options</var>. |
| |
| <p><var>options</var> is a bit string, with the bits as defined by the following |
| single bit masks: |
| |
| <dl> |
| <dt><code>LOG_PERROR</code><dd>If on, <code>openlog</code> sets up the connection so that any <code>syslog</code> |
| on this connection writes its message to the calling process' Standard |
| Error stream in addition to submitting it to Syslog. If off, <code>syslog</code> |
| does not write the message to Standard Error. |
| |
| <br><dt><code>LOG_CONS</code><dd>If on, <code>openlog</code> sets up the connection so that a <code>syslog</code> on |
| this connection that fails to submit a message to Syslog writes the |
| message instead to system console. If off, <code>syslog</code> does not write |
| to the system console (but of course Syslog may write messages it |
| receives to the console). |
| |
| <br><dt><code>LOG_PID</code><dd>When on, <code>openlog</code> sets up the connection so that a <code>syslog</code> |
| on this connection inserts the calling process' Process ID (PID) into |
| the message. When off, <code>openlog</code> does not insert the PID. |
| |
| <br><dt><code>LOG_NDELAY</code><dd>When on, <code>openlog</code> opens and connects the <samp><span class="file">/dev/log</span></samp> socket. |
| When off, a future <code>syslog</code> call must open and connect the socket. |
| |
| <p><strong>Portability note:</strong> In early systems, the sense of this bit was |
| exactly the opposite. |
| |
| <br><dt><code>LOG_ODELAY</code><dd>This bit does nothing. It exists for backward compatibility. |
| |
| </dl> |
| |
| <p>If any other bit in <var>options</var> is on, the result is undefined. |
| |
| <p><var>facility</var> is the default facility code for this connection. A |
| <code>syslog</code> on this connection that specifies default facility causes |
| this facility to be associated with the message. See <code>syslog</code> for |
| possible values. A value of zero means the default default, which is |
| <code>LOG_USER</code>. |
| |
| <p>If a Syslog connection is already open when you call <code>openlog</code>, |
| <code>openlog</code> “reopens” the connection. Reopening is like opening |
| except that if you specify zero for the default facility code, the |
| default facility code simply remains unchanged and if you specify |
| LOG_NDELAY and the socket is already open and connected, <code>openlog</code> |
| just leaves it that way. |
| |
| <!-- There is a bug in closelog() (glibc 2.1.3) wherein it does not reset the --> |
| <!-- default log facility to LOG_USER, which means the default default log --> |
| <!-- facility could be whatever the default log facility was for a previous --> |
| <!-- Syslog connection. I have documented what the function should be rather --> |
| <!-- than what it is because I think if anyone ever gets concerned, the code --> |
| <!-- will change. --> |
| </blockquote></div> |
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