syslog, openlog, closelog, setlogmask - control system log

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SYNOPSIS

#include <syslog.h>

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

void syslog(int priority, char *logstring, /* parameters */ ...);

void closelog(void);

int setlogmask(int maskpri);

MT-LEVEL

Safe

DESCRIPTION

syslog() passes a message to syslogd.1m which may append it to a log file, write it to the system console, or forward it (to either a list of users or syslogd on another host on the network), depending on the configuration of /etc/syslog.conf. logstring is tagged with a priority of priority, and looks like a printf.3b string with one additional allowable format specification, %m, which is replaced with the error message string corresponding to the error number in errno. A trailing NEWLINE is added if needed. Options passed to openlog() may cause the size of the message to expand. The maximum size of the message passed to syslogd is 1024 bytes.

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 bitwise inclusive OR of zero or more of the following flags, defined in the header <syslog.h>.

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.

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. 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.1m 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.1m 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 in.ftpd.1m

LOG_AUTH

The authorization system: login.1 su.1m getty.1m etc.

LOG_LPR

The line printer spooling system: lpr.1b lpc.1b etc.

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

Reserved for local use.

LOG_LOCAL1

Reserved for local use.

LOG_LOCAL2

Reserved for local use.

LOG_LOCAL3

Reserved for local use.

LOG_LOCAL4

Reserved for local use.

LOG_LOCAL5

Reserved for local use.

LOG_LOCAL6

Reserved for local use.

LOG_LOCAL7

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.

EXAMPLES

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.1m 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.1m as other messages to the facility LOG_LOCAL2 are:

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

SEE ALSO

Created by unroff & hp-tools. © by Hans-Peter Bischof. All Rights Reserved (1997).

Last modified 21/April/97