1 files changed, 56 insertions, 8 deletions
diff --git a/manual/syslog.texi b/manual/syslog.texi
index 49f599d93f..df4179e27a 100644
--- a/manual/syslog.texi
+++ b/manual/syslog.texi
@@ -146,8 +146,7 @@ The symbols referred to in this section are declared in the file
 
 @comment syslog.h
 @comment BSD
-@deftypefun void openlog (char *@var{ident}, int @var{option},
-        int @var{facility})
+@deftypefun void openlog (const char *@var{ident}, int @var{option}, int @var{facility})
 
 @code{openlog} opens or reopens a connection to Syslog in preparation
 for submitting messages.
@@ -157,6 +156,46 @@ for submitting messages.
 to identify the source of the message, and people conventionally set it
 to the name of the program that will submit the messages.
 
+If @var{ident} is NULL, or if @code{openlog} is not called, the default
+identification string used in Syslog messages will be the program name,
+taken from argv[0].
+
+Please note that the string pointer @var{ident} will be retained
+internally by the Syslog routines.  You must not free the memory that
+@var{ident} 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} string,
+you must call @code{openlog} again; overwriting the string pointed to by
+@var{ident} is not thread-safe.
+
+You can cause the Syslog routines to drop the reference to @var{ident} and
+go back to the default string (the program name taken from argv[0]), by
+calling @code{closelog}: @xref{closelog}.
+
+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},
+you must call @code{closelog} before any point where your library might
+get unloaded, as in this example:
+
+@smallexample
+#include <syslog.h>
+
+void
+shared_library_function (void)
+@{
+  openlog ("mylibrary", option, priority);
+
+  syslog (LOG_INFO, "shared library has been invoked");
+
+  closelog ();
+@}
+@end smallexample
+
+Without the call to @code{closelog}, future invocations of @code{syslog}
+by the program using the shared library may crash, if the library gets
+unloaded and the memory containing the string @code{"mylibrary"} becomes
+unmapped.  This is a limitation of the BSD syslog interface.
+
 @code{openlog} may or may not open the @file{/dev/log} socket, depending
 on @var{option}.  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
@@ -383,12 +422,21 @@ The symbols referred to in this section are declared in the file
 @deftypefun void closelog (void)
 
 @code{closelog} closes the current Syslog connection, if there is one.
-This include closing the @file{dev/log} socket, if it is open.
-
-There is very little reason to use this function.  It does not flush any
-buffers; you can reopen a Syslog connection without closing it first;
-The connection gets closed automatically on exec or exit.
-@code{closelog} has primarily aesthetic value.
+This includes closing the @file{dev/log} socket, if it is open.
+@code{closelog} also sets the identification string for Syslog messages
+back to the default, if @code{openlog} was called with a non-NULL argument
+to @var{ident}.  The default identification string is the program name
+taken from argv[0].
+
+If you are writing shared library code that uses @code{openlog} to
+generate custom syslog output, you should use @code{closelog} to drop the
+GNU C library's internal reference to the @var{ident} pointer when you are
+done.  Please read the section on @code{openlog} for more information:
+@xref{openlog}.
+
+@code{closelog} does not flush any buffers.  You do not have to call
+@code{closelog} before re-opening a Syslog connection with @code{initlog}.
+Syslog connections are automatically closed on exec or exit.
 
 @end deftypefun