syslog(3) - Linux manual page (original) (raw)
syslog(3) Library Functions Manual syslog(3)
NAME top
closelog, openlog, syslog, vsyslog - send messages to the system
loggerLIBRARY top
Standard C library (_libc_, _-lc_)SYNOPSIS top
**#include <syslog.h>**
**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)):
**vsyslog**():
Since glibc 2.19:
_DEFAULT_SOURCE
glibc 2.19 and earlier:
_BSD_SOURCEDESCRIPTION top
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).
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)](../man3/printf.3.html), and any
arguments required by the _format_, except that the two-character
sequence **%m** will be replaced by the error message string
_strerror_(_[errno](../man3/errno.3.html)_). 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)](../man3/stdarg.3.html) variable argument list macros.closelog() closelog() closes the file descriptor being used to write to the system logger. The use of closelog() is optional.
[1mValues 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)](../man2/chroot.2.html) 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.[1mValues 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)
**LOG_USER** (default)
generic user-level messages
**LOG_UUCP**
UUCP subsystem[1mValues 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)](../man3/setlogmask.3.html) can be used to restrict logging to
specified levels only.ATTRIBUTES top
For an explanation of the terms used in this section, see
[attributes(7)](../man7/attributes.7.html).
┌───────────────────────────┬───────────────┬────────────────────┐
│ **Interface** │ **Attribute** │ **Value** │
├───────────────────────────┼───────────────┼────────────────────┤
│ **openlog**(), **closelog**() │ Thread safety │ MT-Safe │
├───────────────────────────┼───────────────┼────────────────────┤
│ **syslog**(), **vsyslog**() │ Thread safety │ MT-Safe env locale │
└───────────────────────────┴───────────────┴────────────────────┘STANDARDS top
**syslog**()
**openlog**()
**closelog**()
POSIX.1-2008.
**vsyslog**()
None.HISTORY top
**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 top
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 top
[journalctl(1)](../man1/journalctl.1.html), [logger(1)](../man1/logger.1.html), [setlogmask(3)](../man3/setlogmask.3.html), **syslog.conf**(5),
**syslogd**(8)COLOPHON top
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man-pages@man7.orgLinux man-pages 6.10 2024-07-23 syslog(3)
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