syslog, openlog, closelog, setlogmask, vsyslog - control system log
void openlog(const char *ident, int logopt, int facility);
void syslog(int priority, const char *message, parameters...);
int setlogmask(int maskpri);
void vsyslog(int priority, const char *message, va_list ap);
Syslog arranges to write message onto the system log maintained by
syslogd(1M). The message is tagged with 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.
This message will be read by syslogd(1M) and written to the system
console, log files, or forwarded to syslogd on another host as
appropriate. Vsyslog is like syslog except that instead of being called
with a variable number of arguments, it is called with an argument list
as defined by stdarg(5).
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
LOG_ALERT A condition that should be corrected immediately, such as a
corrupted system database.
LOG_CRIT Critical conditions, e.g., hard device errors.
LOG_WARNING Warning messages.
LOG_NOTICE Conditions that are not error conditions, but should
possibly be handled specially.
LOG_INFO Informational messages.
LOG_DEBUG Messages that contain information normally of use only when
debugging a program.
If syslog cannot pass the message to syslogd, it will attempt to write
the message on /dev/console if the LOG_CONS option is set (see below).
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: useful for
identifying instantiations of daemons.
LOG_CONS Force writing messages to the console if unable to send it
to syslogd. This option is safe to use in daemon processes
that have no controlling terminal since syslog will fork
before opening the console.
LOG_ODELAY Delay opening the connection to syslogd until the first
syslog call. This is the default.
LOG_NDELAY Open the connection to syslogd immediately. Useful for
programs that need to manage the order in which file
descriptors are allocated.
LOG_NOWAIT Don't wait for children forked to log messages on the
console. This option should be used by processes that
enable notification of child termination via SIGCHLD, as
syslog may otherwise block waiting for a child whose exit
status has already been collected.
LOG_PERROR Write messages to stderr as well as to syslogd.
The facility parameter encodes a default facility to be assigned to all
messages that do not have an explicit facility 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 routed(1M), ftpd(1M), rshd(1M),
LOG_AUTH The authorization system: login(1), su(1M), getty(1M),
etc. ftpd(1M), and rshd(1M) also use LOG_AUTH.
LOG_LPR The line printer spooling system: lpr(1), lpd(1M), etc.
LOG_NEWS The network news system.
LOG_UUCP The UNIX-to-UNIX Copy system: uucp(1C), uucico(1M),
LOG_LOCAL0 Reserved for local use. Similarly for LOG_LOCAL1 through
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.
A call to openlog does not make a copy of the ident parameter, it merely
stores a pointer to it. This means that the caller cannot re-use the
memory in which the string is stored.
syslog(LOG_ALERT, "who: internal error 23");
openlog("ftpd", LOG_PID, LOG_DAEMON);
syslog(LOG_INFO, "Connection from host %d", CallingHost);
syslog(LOG_INFO|LOG_LOCAL2, "foobar error: %m");
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