NAME

syslog , vsyslog , openlog , closelog , setlogmask − control system log

SYNOPSIS

#include <syslog.h>
#include <varargs.h>

void syslog(priority, message, ...);
int priority;
char ∗message;

void vsyslog(priority, message, args);
int priority;
char ∗message;
va_list args;

void openlog(ident, logopt, facility);
char ∗ident;
int logopt;
int facility;

void closelog();

int setlogmask(maskpri);
int maskpri;

DESCRIPTION

The syslog() function writes message to the system message logger.  The message is then written to the system console, log files, logged-in users, or forwarded to other machines as appropriate. (See syslogd(8)).

The message is identical to a printf(3) format string, except that %m is replaced by the current error message as denoted by the global variable errno.  See strerror(3)). A trailing newline is added if none is present.

The vsyslog() function is an alternate form in which the arguments have already been captured using the variable-length argument facilities of varargs(3).

The message is tagged with priority. 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 the following ordered (high to low) list:

LOG_EMERGA panic condition.  This is normally broadcast to all users. 

LOG_ALERTA condition that should be corrected immediately, such as a corrupted system database. 

LOG_CRITCritical conditions, e.g., hard device errors. 

LOG_ERRErrors. 

LOG_WARNINGWarning messages. 

LOG_NOTICEConditions that are not error conditions, but should possibly be handled specially. 

LOG_INFOInformational messages. 

LOG_DEBUGMessages that contain information normally of use only when debugging a program. 

The openlog() function provides for more specialized processing of the messages sent by syslog() and vsyslog(). The parameter ident is a string that will be prepended to every message.  The logopt argument is a bit field specifying logging options, which is formed by OR’ing one or more of the following values:

LOG_CONSIf syslog cannot pass the message to syslogd it will attempt to write the message to the console (/dev/console). 

LOG_NDELAYOpen the connection to syslogd immediately.  Normally the open is delayed until the first message is logged.  Useful for programs that need to manage the order in which file descriptors are allocated. 

LOG_PERRORWrite the message to standard error output as well to the system log. 

LOG_PIDLog the process id with each message: useful for identifying instantiations of daemons. 

The facility parameter encodes a default facility to be assigned to all messages that do not have an explicit facility encoded:

LOG_AUTHThe authorization system: login(1), su(1), getty(8), etc.

LOG_AUTHPRIVThe same as LOG_AUTH , but logged to a file readable only by selected individuals. 

LOG_CRONThe clock daemon. 

LOG_DAEMONSystem daemons, such as routed(8), that are not provided for explicitly by other facilities.

LOG_KERNMessages generated by the kernel.  These cannot be generated by any user processes. 

LOG_LPRThe line printer spooling system: lpr(1), lpc(8), lpd(8), etc.

LOG_MAILThe mail system. 

LOG_NEWSThe network news system. 

LOG_SYSLOGMessages generated internally by syslogd(8).

LOG_USERMessages generated by random user processes.  This is the default facility identifier if none is specified. 

LOG_UUCPThe uucp system. 

LOG_LOCAL0Reserved for local use.  Similarly for LOG_LOCAL1 through LOG_LOCAL7. 

The closelog function can be used to close the log file. 

The setlogmask function 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.

RETURN VALUES

The routines closelog(), openlog(), syslog() and vsyslog() return no value.

The routine setlogmask() always returns the previous log mask level.

EXAMPLES

syslog(LOG_ALERT, "who: internal error 23");
 
openlog("ftpd", LOG_PID, LOG_DAEMON); setlogmask(LOG_UPTO(LOG_ERR)); syslog(LOG_INFO, "Connection from host %d", CallingHost);
 
syslog(LOG_INFO|LOG_LOCAL2, "foobar error: %m");

SEE ALSO

logger(1), syslogd(8)

BUGS

Under 2.11BSD the logfile /usr/adm/messages is used if a non networking kernel has been booted.  That file must be publically writeable in this case. 

HISTORY

These functions appeared in 4.2BSD. 

4.2 Berkeley Distribution  —  April 1, 1995