SYSLOG
Section: Linux Programmer's Manual (3)
Updated: 2008-11-12
NAME
closelog, openlog, syslog, vsyslog - send messages to the system logger
SYNOPSIS
#include <syslog.h>
void openlog(const char *ident, int option, int facility);
void syslog(int priority, const char *format, ...);
void closelog(void);
#include <stdarg.h>
void vsyslog(int priority, const char *format, va_list ap);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
vsyslog():
_BSD_SOURCE
DESCRIPTION
closelog()
closes the descriptor being used to write to the system logger.
The use of
closelog()
is optional.
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.
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().
Values for
option
and
facility
are given 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()
generates a log message, which will be distributed by
syslogd(8).
The
priority
argument is formed by ORing the
facility
and the
level
values (explained below).
The remaining arguments
are a
format,
as in
printf(3)
and any arguments required by the
format,
except that the two character sequence
%m
will be replaced by
the error message string
strerror(errno).
A trailing newline may be added if needed.
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)
variable argument list macros.
The subsections below list the parameters used to set the values of
option, facility, and priority.
option
The
option
argument to
openlog()
is an OR of any of these:
- LOG_CONS
-
Write directly to system console if there is an error while sending to
system logger.
- LOG_NDELAY
-
Open the connection immediately (normally, the connection is opened when
the first message is logged).
- 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.)
Print to stderr as well.
- LOG_PID
-
Include PID with each message.
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 (DEPRECATED Use
LOG_AUTHPRIV
instead)
- 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
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)
can be used to restrict logging to specified levels only.
CONFORMING TO
The functions
openlog(),
closelog(),
and
syslog()
(but not
vsyslog())
are specified in SUSv2 and POSIX.1-2001.
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, 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
logger(1),
setlogmask(3),
syslog.conf(5),
syslogd(8)
COLOPHON
This page is part of release 3.27 of the Linux
man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
http://www.kernel.org/doc/man-pages/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- option
-
- facility
-
- level
-
- CONFORMING TO
-
- NOTES
-
- SEE ALSO
-
- COLOPHON
-
This document was created by
man2html,
using the manual pages.
Time: 07:35:16 GMT, March 26, 2013