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); |
void
vsyslog( |
int priority, |
| const char *format, | |
va_list ap); |
![[Note]](../stylesheet/note.png) |
Note | ||||
|---|---|---|---|---|---|
|
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).
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), 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) 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) 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 untilsyslog() 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_LOCAL0throughLOG_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
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) can be used to restrict logging to specified levels only.
ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).
| Interface | Attribute | Value |
openlog(), closelog() |
Thread safety | MT-Safe |
syslog(), vsyslog() |
Thread safety | MT-Safe env locale |
CONFORMING TO
The functions openlog(),
closelog(), and syslog() (but not vsyslog()) are specified in SUSv2,
POSIX.1-2001, and POSIX.1-2008.
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);
COLOPHON
This page is part of release 5.11 of the Linux man-pages project. A
description of the project, information about reporting bugs,
and the latest version of this page, can be found at
https://www.kernel.org/doc/man−pages/.
|
Written Feb 1994 by Steve Greenland (stevegrneosoft.com) and Copyright 2001, 2017 Michael Kerrisk <mtk.manpagesgmail.com> %%%LICENSE_START(VERBATIM) 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 manual under the conditions for verbatim copying, provided that the 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 have taken the same level of care in the production of this manual, which is licensed free of charge, as they might when working professionally. Formatted or processed versions of this manual, if unaccompanied by the source, must acknowledge the copyright and authors of this work. %%%LICENSE_END 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> |