Tribblix: manual page: syslog.3c

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(8), 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
message header consists of a facility indicator, a severity level
indicator, 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(3C), 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
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.

LOG_AUTH
The authentication / security / authorization system:
login(1), su(8), getty(8).

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(8).

LOG_AUDIT
The audit facility, for example, auditd(8).

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 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 processes (for daemons
that fork).

LOG_CONS
Write messages to the system console if they cannot be
sent to syslogd(8). 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(8) 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
argument 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(8) 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
following 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(8) as
other messages to the facility LOG_LOCAL2 are:

syslog(LOG_INFO|LOG_LOCAL2, "error: %m");

ATTRIBUTES