syslog(3) (BSD Compatibility Package) syslog(3)
NAME
syslog, openlog, closelog, setlogmask - control system log
SYNOPSIS
cc [ flag... ] file ... -lucb
#include <syslog.h>
openlog(ident, logopt, facility)
char *ident;
syslog(priority, message, parameters ... )
char *message;
closelog()
setlogmask(maskpri)
DESCRIPTION
syslog passes message to syslogd(1M), which logs it in an appropriate
system log, writes it to the system console, forwards it to a list of
users, or forwards it to the syslogd on another host over the
network. The message is tagged with a priority of priority. The
message looks like a printf(3S) string except that %m is replaced by
the current error message (collected from errno). A trailing NEWLINE
is added if needed.
Priorities are encoded as a facility and a level. The facility
describes the part of the system generating the message. The level
is selected from an ordered list:
LOGEMERG A panic condition. This is normally
broadcast to all users.
LOGALERT A condition that should be corrected
immediately, such as a corrupted system
database.
LOGCRIT Critical conditions, such as hard device
errors.
LOGERR Errors.
LOGWARNING Warning messages.
LOGNOTICE Conditions that are not error conditions,
but that may require special handling.
LOGINFO Informational messages.
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LOGDEBUG Messages that contain information normally
of use only when debugging a program.
If special processing is needed, openlog can be called to initialize
the log file. The parameter ident is a string that is prepended to
every message. logopt is a bit field indicating logging options.
Current values for logopt are:
LOGPID Log the process ID with each message. This
is useful for identifying specific daemon
processes (for daemons that fork).
LOGCONS Write messages to the system console if
they cannot be sent to syslogd. This
option is safe to use in daemon processes
that have no controlling terminal, since
syslog forks before opening the console.
LOGNDELAY Open the connection to syslogd 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.
LOGNOWAIT 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 parameter encodes a default facility to be assigned to
all messages that do not have an explicit facility already encoded:
LOGKERN Messages generated by the kernel. These
cannot be generated by any user processes.
LOGUSER Messages generated by random user
processes. This is the default facility
identifier if none is specified.
LOGMAIL The mail system.
LOGDAEMON System daemons, such as ftpd(1M),
routed(1M), etc.
LOGAUTH The authorization system: login(1), su(1),
getty(1M), etc.
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LOGLPR The line printer spooling system: lpr(1),
lpc(1M), etc.
LOGNEWS Reserved for the USENET network news
system.
LOGUUCP Reserved for the UUCP system; it does not
currently use syslog.
LOGCRON The cron/at facility; crontab(1), at(1),
cron(1M), etc.
LOGLOCAL0-7 Reserved for local use.
closelog can be used to close the log file.
setlogmask sets the log priority mask to maskpri and returns the
previous mask. Calls to syslog with a priority not set in maskpri
are rejected. The mask for an individual priority pri is calculated
by the macro LOGMASK(pri); the mask for all priorities up to and
including toppri is given by the macro LOGUPTO(toppri). The default
allows all priorities to be logged.
EXAMPLE
This call logs a message at priority LOGALERT:
syslog(LOGALERT, "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 as other messages from system daemons
are, and should include the process ID of the process logging the
message:
openlog("ftpd", LOGPID, LOGDAEMON);
Then it would make the following call to setlogmask to indicate that
messages at priorities from LOGEMERG through LOGERR should be
logged, but that no messages at any other priority should be logged:
setlogmask(LOGUPTO(LOG_ERR));
Then, to log a message at priority LOGINFO, it would make the
following call to syslog:
syslog(LOGINFO, "Connection from host %d", CallingHost);
A locally-written utility could use the following call to syslog to
log a message at priority LOGINFO, to be treated by syslogd as other
messages to the facility LOGLOCAL2 are treated:
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syslog(LOGINFO|LOGLOCAL2, "error: %m");
SEE ALSO
logger(1), login(1), lpr(1), lpc(1M), syslogd(1M), printf(3S)
at(1), crontab(1), login(1) in the User's Reference Manual.
ftpd(1M), routed(1M) in the Network User's and Administrator's Guide.
getty(1M), cron(1M), su(1), printf(3S) in the System Administrator's
Reference Manual.
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