openlog(3C)
NAME
syslog, openlog, closelog, setlogmask - control system log
SYNOPSIS
#include <syslog.h>
void openlog(const char *ident, int logopt, int facility);
void syslog(int priority, const char *message, .../* argu-
ments */);
void closelog(void);
int setlogmask(int maskpri);
DESCRIPTION
The syslog() function sends a message to syslogd(1M), which,
depending on the configuration of /etc/syslog.conf, logs it
in an appropriate system log, writes it to the system con-
sole, forwards it to a list of users, or forwards it to sys-
logd on another host over the network. The logged message
includes a message header and a message body. The message
header consists of a facility indicator, a severity level
indicator, a timestamp, a tag string, and optionally the
process ID.
The message body is generated from the message and following
arguments in the same manner as if these were arguments to
printf(3UCB), except that occurrences of %m in the format
string pointed to by the message argument are replaced by
the error message string associated with the current value
of errno. A trailing NEWLINE character is added if needed.
Values of the priority argument are formed by ORing together
a severity level value and an optional facility value.
If no facility value is specified, the current default
facility value is used.
Possible values of severity level include:
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.
The facility indicates the application or system component
generating the message. Possible facility values include:
LOG_KERN
Messages generated by the kernel. These cannot be gen-
erated 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).
LOG_LPR
The line printer spooling system: lpr(1B), lpc(1B).
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).
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.
The openlog() function sets process attributes that affect
subsequent calls to syslog(). The ident argument is a string
that is prepended to every message. The logopt argument
indicates logging options. Values for logopt are con-
structed by a bitwise-inclusive OR of zero or more of the
following:
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. Nor-
mally 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 allo-
cated.
LOG_ODELAY
Delay open until syslog() is called.
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 other-
wise block waiting for a child whose exit status has
already been collected.
The facility argument encodes a default facility to be
assigned to all messages that do not have an explicit facil-
ity already encoded. The initial default facility is
LOG_USER.
The openlog() and syslog() functions may allocate a file
descriptor. It is not necessary to call openlog() prior to
calling syslog().
The closelog() function closes any open file descriptors
allocated by previous calls to openlog() or syslog().
The setlogmask() function sets the log priority mask for the
current process to maskpri and returns the previous mask.
If the maskpri argument is 0, the current log mask is not
modified. Calls by the current process 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 includ-
ing toppri is given by the macro LOG_UPT(toppri). The
default log mask allows all priorities to be logged.
Symbolic constants for use as values of the logopt, facil-
ity, priority, and maskpri arguments are defined in the
<syslog.h> header.
RETURN VALUES
The setlogmask() function returns the previous log priority
mask. The closelog(), openlog() and syslog() functions
return no value.
ERRORS
No errors are defined.
EXAMPLES
Example 1: Example of LOG_ALERT message.
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 identify-
ing 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");
ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| MT-Level | Safe |
|_____________________________|_____________________________|
SEE ALSO
at(1), crontab(1), logger(1), login(1), lpc(1B), lpr(1B),
cron(1M), getty(1M), in.ftpd(1M), su(1M), syslogd(1M),
printf(3UCB), syslog.conf(4), attributes(5)
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