syslog(3) UNIX System V(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:
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.
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syslog(3) UNIX System V(BSD Compatibility Package) syslog(3)
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:
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. 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 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_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 parameter encodes a default facility to be assigned to all
messages that do not have an explicit facility already encoded:
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 ftpd(1M), routed(1M),
etc.
LOG_AUTH The authorization system: login(1), su(1),
getty(1M), etc.
LOG_LPR The line printer spooling system: lpr(1),
lpc(1M), etc.
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syslog(3) UNIX System V(BSD Compatibility Package) syslog(3)
LOG_NEWS Reserved for the USENET network news system.
LOG_UUCP Reserved for the UUCP system; it does not
currently use syslog.
LOG_CRON The cron/at facility; crontab(1), at(1),
cron(1M), etc.
LOG_LOCAL0-7 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
LOG_MASK(pri); the mask for all priorities up to and including toppri is
given by the macro LOG_UPTO(toppri). The default allows all priorities
to be logged.
EXAMPLE
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 as other messages from system daemons are, and 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 as other messages
to the facility LOG_LOCAL2 are treated:
syslog(LOG_INFO|LOG_LOCAL2, "error: %m");
SEE ALSO
logger(1), login(1), lpr(1), lpc(1M), syslogd(1M), printf(3S)
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syslog(3) UNIX System V(BSD Compatibility Package) syslog(3)
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), in the System Administrator's Reference
Manual
printf(3S) in the Programmer's Reference Manual
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