--- name: "closelog" section: "3" platform: "linux" package: "man-pages" version: "6.19-1" release: "Arch Linux 2026-11-01" platforms: ["linux", "freebsd"] url: "https://new.carta.tech/syslog/3" --- # closelog(3) send messages to the system logger Part of [syslog(3)](/syslog/3.md). ## NAME closelog, openlog, syslog, vsyslog - send messages to the system logger ## LIBRARY Standard C library (*libc*, *-lc*) ## SYNOPSIS ``` #include ``` **void openlog(const char \****ident***, int** *option***, int** *facility***);** **void syslog(int** *priority***, const char \****format***, ...);** **void closelog(void);** **void vsyslog(int** *priority***, const char \****format***, va\_list** *ap***);** Feature Test Macro Requirements for glibc (see [**feature\_test\_macros**(7)](/feature_test_macros/7.md)): **vsyslog**(): ``` Since glibc 2.19: _DEFAULT_SOURCE glibc 2.19 and earlier: _BSD_SOURCE ``` ## DESCRIPTION ### openlog() **openlog**() opens a connection to the system logger for a program. The string pointed to by *ident* is prepended to every message, and is typically set to the program name. If *ident* is NULL, the program name is used. (POSIX.1-2008 does not specify the behavior when *ident* is NULL.) The *option* argument specifies flags which control the operation of **openlog**() and subsequent calls to **syslog**(). The *facility* argument establishes a default to be used if none is specified in subsequent calls to **syslog**(). The values that may be specified for *option* and *facility* are described below. The use of **openlog**() is optional; it will automatically be called by **syslog**() if necessary, in which case *ident* will default to NULL. ### syslog() and vsyslog() **syslog**() generates a log message, which will be distributed by [**syslogd**(8)](/syslogd/8.md). The *priority* argument is formed by ORing together a *facility* value and a *level* value (described below). If no *facility* value is ORed into *priority*, then the default value set by **openlog**() is used, or, if there was no preceding **openlog**() call, a default of **LOG\_USER** is employed. The remaining arguments are a *format*, as in [**printf**(3)](/printf/3.md), and any arguments required by the *format*, except that the two-character sequence **%m** will be replaced by the error message string *strerror*(*errno*). The format string need not include a terminating newline character. The function **vsyslog**() performs the same task as **syslog**() with the difference that it takes a set of arguments which have been obtained using the [**stdarg**(3)](/stdarg/3.md) variable argument list macros. ### closelog() **closelog**() closes the file descriptor being used to write to the system logger. The use of **closelog**() is optional. ### Values for *option* The *option* argument to **openlog**() is a bit mask constructed by ORing together any of the following values: - **LOG\_CONS** Write directly to the system console if there is an error while sending to the system logger. - **LOG\_NDELAY** Open the connection immediately (normally, the connection is opened when the first message is logged). This may be useful, for example, if a subsequent [**chroot**(2)](/chroot/2.md) would make the pathname used internally by the logging facility unreachable. - **LOG\_NOWAIT** Don't wait for child processes that may have been created while logging the message. (The GNU C library does not create a child process, so this option has no effect on Linux.) - **LOG\_ODELAY** The converse of **LOG\_NDELAY**; opening of the connection is delayed until **syslog**() is called. (This is the default, and need not be specified.) - **LOG\_PERROR** (Not in POSIX.1-2001 or POSIX.1-2008.) Also log the message to *stderr*. - **LOG\_PID** Include the caller's PID with each message. ### Values for *facility* The *facility* argument is used to specify what type of program is logging the message. This lets the configuration file specify that messages from different facilities will be handled differently. - **LOG\_AUTH** security/authorization messages - **LOG\_AUTHPRIV** security/authorization messages (private) - **LOG\_CRON** clock daemon (**cron** and **at**) - **LOG\_DAEMON** system daemons without separate facility value - **LOG\_FTP** ftp daemon - **LOG\_KERN** kernel messages (these can't be generated from user processes) - **LOG\_LOCAL0** through **LOG\_LOCAL7** reserved for local use - **LOG\_LPR** line printer subsystem - **LOG\_MAIL** mail subsystem - **LOG\_NEWS** USENET news subsystem - **LOG\_SYSLOG** messages generated internally by [**syslogd**(8)](/syslogd/8.md) - **LOG\_USER** (default) generic user-level messages - **LOG\_UUCP** UUCP subsystem ### Values for *level* This determines the importance of the message. The levels are, in order of decreasing importance: - **LOG\_EMERG** system is unusable - **LOG\_ALERT** action must be taken immediately - **LOG\_CRIT** critical conditions - **LOG\_ERR** error conditions - **LOG\_WARNING** warning conditions - **LOG\_NOTICE** normal, but significant, condition - **LOG\_INFO** informational message - **LOG\_DEBUG** debug-level message The function [**setlogmask**(3)](/setlogmask/3.md) can be used to restrict logging to specified levels only. ## ATTRIBUTES For an explanation of the terms used in this section, see [**attributes**(7)](/attributes/7.md). | | | | | --- | --- | --- | | **Interface** | **Attribute** | **Value** | | **openlog**(), **closelog**() | Thread safety | MT-Safe | | **syslog**(), **vsyslog**() | Thread safety | MT-Safe env locale | ## STANDARDS - **syslog**() **openlog**() **closelog**() POSIX.1-2008. - **vsyslog**() None. ## HISTORY - **syslog**() 4\.2BSD, SUSv2, POSIX.1-2001. - **openlog**() **closelog**() 4\.3BSD, SUSv2, POSIX.1-2001. - **vsyslog**() 4\.3BSD-Reno. POSIX.1-2001 specifies only the **LOG\_USER** and **LOG\_LOCAL\*** values for *facility*. However, with the exception of **LOG\_AUTHPRIV** and **LOG\_FTP**, the other *facility* values appear on most UNIX systems. The **LOG\_PERROR** value for *option* is not specified by POSIX.1-2001 or POSIX.1-2008, but is available in most versions of UNIX. ## NOTES The argument *ident* in the call of **openlog**() is probably stored as-is. Thus, if the string it points to is changed, **syslog**() may start prepending the changed string, and if the string it points to ceases to exist, the results are undefined. Most portable is to use a string constant. Never pass a string with user-supplied data as a format, use the following instead: ``` syslog(priority, "%s", string); ``` ## SEE ALSO [**journalctl**(1)](/journalctl/1.md), [**logger**(1)](/logger/1.md), [**setlogmask**(3)](/setlogmask/3.md), [**syslog.conf**(5)](/syslog.conf/5.md), [**syslogd**(8)](/syslogd/8.md)