SYSLOG(3C)SYSLOG(3C)NAME
syslog, openlog, closelog, setlogmask - control system log
SYNOPSIS
#include <syslog.h>
void openlog(const char *ident, int logopt, int facility);
void syslog(int priority, const char *message, .../* arguments */);
void closelog(void);
int setlogmask(int maskpri);
DESCRIPTION
The syslog() function sends a message to syslogd(1M), which, depending
on the configuration of /etc/syslog.conf, logs it in an appropriate
system log, writes it to the system console, forwards it to a list of
users, or forwards it to syslogd on another host over the network. The
logged message includes a message header and a message body. The mes‐
sage header consists of a facility indicator, a severity level indica‐
tor, a timestamp, a tag string, and optionally the process ID.
The message body is generated from the message and following arguments
in the same manner as if these were arguments to printf(3UCB), except
that occurrences of %m in the format string pointed to by the message
argument are replaced by the error message string associated with the
current value of errno. A trailing NEWLINE character is added if
needed.
Symbolic constants for use as values of the logopt, facility, priority,
and maskpri arguments are defined in the <syslog.h> header.
Values of the priority argument are formed by ORing together a severity
level value and an optional facility value. If no facility value is
specified, the current default facility value is used.
Possible values of severity level include, in decreasing order:
LOG_EMERG
A panic condition. This is normally broadcast to all
users.
LOG_ALERT
A condition that should be corrected immediately, such
as a corrupted system database.
LOG_CRIT
Critical conditions, such as hard device errors.
LOG_ERR
Errors.
LOG_WARNING
Warning messages.
LOG_NOTICE
Conditions that are not error conditions, but that may
require special handling.
LOG_INFO
Informational messages.
LOG_DEBUG
Messages that contain information normally of use only
when debugging a program.
The facility indicates the application or system component generating
the message. Possible facility values include:
LOG_KERN
Messages generated by the kernel. These cannot be gener‐
ated by any user processes.
LOG_USER
Messages generated by random user processes. This is the
default facility identifier if none is specified.
LOG_MAIL
The mail system.
LOG_DAEMON
System daemons, such as in.ftpd(1M).
LOG_AUTH
The authentication / security / authorization system:
login(1), su(1M), getty(1M).
LOG_LPR
The line printer spooling system: lpr(1B), lpc(1B).
LOG_NEWS
Designated for the USENET network news system.
LOG_UUCP
Designated for the UUCP system; it does not currently use
syslog().
LOG_CRON
The cron/at facility; crontab(1), at(1), cron(1M).
LOG_AUDIT
The audit facility, for example, auditd(1M).
LOG_LOCAL0
Designated for local use.
LOG_LOCAL1
Designated for local use.
LOG_LOCAL2
Designated for local use.
LOG_LOCAL3
Designated for local use.
LOG_LOCAL4
Designated for local use.
LOG_LOCAL5
Designated for local use.
LOG_LOCAL6
Designated for local use.
LOG_LOCAL7
Designated for local use.
The openlog() function sets process attributes that affect subsequent
calls to syslog(). The ident argument is a string that is prepended to
every message. The openlog() function uses the passed-in ident argument
directly, rather than making a private copy of it. The logopt argument
indicates logging options. Values for logopt are constructed by a bit‐
wise-inclusive OR of zero or more of the following:
LOG_PID
Log the process ID with each message. This is useful for
identifying specific daemon processes (for daemons that
fork).
LOG_CONS
Write messages to the system console if they cannot be
sent to syslogd(1M). This option is safe to use in daemon
processes that have no controlling terminal, since sys‐
log() forks before opening the console.
LOG_NDELAY
Open the connection to syslogd(1M) immediately. Normally
the open is delayed until the first message is logged.
This is useful for programs that need to manage the order
in which file descriptors are allocated.
LOG_ODELAY
Delay open until syslog() is called.
LOG_NOWAIT
Do not wait for child processes that have been forked to
log messages onto the console. This option should be
used by processes that enable notification of child ter‐
mination using SIGCHLD, since syslog() may otherwise
block waiting for a child whose exit status has already
been collected.
The facility argument encodes a default facility to be assigned to all
messages that do not have an explicit facility already encoded. The
initial default facility is LOG_USER.
The openlog() and syslog() functions may allocate a file descriptor.
It is not necessary to call openlog() prior to calling syslog().
The closelog() function closes any open file descriptors allocated by
previous calls to openlog() or syslog().
The setlogmask() function sets the log priority mask for the current
process to maskpri and returns the previous mask. If the maskpri argu‐
ment is 0, the current log mask is not modified. Calls by the current
process to syslog() with a priority not set in maskpri are rejected.
The mask for an individual priority pri is calculated by the macro
LOG_MASK(pri); the mask for all priorities up to and including toppri
is given by the macro LOG_UPTO(toppri). The default log mask allows all
priorities to be logged.
RETURN VALUES
The setlogmask() function returns the previous log priority mask. The
closelog(), openlog() and syslog() functions return no value.
ERRORS
No errors are defined.
EXAMPLES
Example 1 Example of LOG_ALERT message.
This call logs a message at priority LOG_ALERT:
syslog(LOG_ALERT, "who: internal error 23");
The FTP daemon ftpd would make this call to openlog() to indicate that
all messages it logs should have an identifying string of ftpd, should
be treated by syslogd(1M) as other messages from system daemons are,
should include the process ID of the process logging the message:
openlog("ftpd", LOG_PID, LOG_DAEMON);
Then it would make the following call to setlogmask() to indicate that
messages at priorities from LOG_EMERG through LOG_ERR should be logged,
but that no messages at any other priority should be logged:
setlogmask(LOG_UPTO(LOG_ERR));
Then, to log a message at priority LOG_INFO, it would make the follow‐
ing call to syslog:
syslog(LOG_INFO, "Connection from host %d", CallingHost);
A locally-written utility could use the following call to syslog() to
log a message at priority LOG_INFO to be treated by syslogd(1M) as
other messages to the facility LOG_LOCAL2 are:
syslog(LOG_INFO|LOG_LOCAL2, "error: %m");
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
┌────────────────────┬───────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├────────────────────┼───────────────────┤
│Interface Stability │ Committed │
├────────────────────┼───────────────────┤
│MT-Level │ Safe │
├────────────────────┼───────────────────┤
│Standard │ See standards(5). │
└────────────────────┴───────────────────┘
SEE ALSOat(1), crontab(1), logger(1), login(1), lpc(1B), lpr(1B), auditd(1M),
cron(1M), getty(1M), in.ftpd(1M), su(1M), syslogd(1M), printf(3UCB),
syslog.conf(4), attributes(5), standards(5)
Mar 16, 2009 SYSLOG(3C)