syslog(3C) Standard C Library Functions 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 immedi‐
ately, 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 generated 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 logopt argument indicates logging options. Values
for logopt are constructed by a bitwise-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 pro‐
cesses (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 syslog() 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 termination 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 │Standard │
├─────────────────────────────┼─────────────────────────────┤
│MT-Level │Safe │
└─────────────────────────────┴─────────────────────────────┘
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)SunOS 5.10 28 Jul 2004 syslog(3C)