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);
[Note] Note
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 lists 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

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 parameter 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 2.79 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/.


  Written  Feb 1994 by Steve Greenland (stevegrneosoft.com)

Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.

Permission is granted to copy and distribute modified versions of this
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entire resulting derived work is distributed under the terms of a
permission notice identical to this one.

Since the Linux kernel and libraries are constantly changing, this
manual page may be incorrect or out-of-date.  The author(s) assume no
responsibility for errors or omissions, or for damages resulting from
the use of the information contained herein.  The author(s) may not
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which is licensed free of charge, as they might when working
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Formatted or processed versions of this manual, if unaccompanied by
the source, must acknowledge the copyright and authors of this work.

Updated 1999.12.19 by Karl M. Hegbloom <karlhegdebian.org>

Updated 13 Oct 2001, Michael Kerrisk <mtk.manpagesgmail.com>
Added description of vsyslog
Added descriptions of LOG_ODELAY and LOG_NOWAIT
Added brief description of facility and option arguments
Added CONFORMING TO section
2001-10-13, aeb, minor changes
Modified 13 Dec 2001, Martin Schulze <joeyinfodrom.org>
Modified 3 Jan 2002, Michael Kerrisk <mtk.manpagesgmail.com>