The Single UNIX ® Specification, Version 2
Copyright © 1997 The Open Group


closelog, openlog, setlogmask, syslog - control system log


#include <syslog.h>

void closelog(void);
void openlog(const char *ident, int logopt, int facility);
int setlogmask(int maskpri);
void syslog(int priority, const char *message, ... /* arguments */);


The syslog() function sends a message to an implementation-dependent logging facility, which may log it in an implementation-dependent system log, write it to the system console, forward it to a list of users, or forward it to the logging facility on another host over the network. The logged message includes a message header and a message body. The message header contains at least a timestamp and a tag string.

The message body is generated from the message and following arguments in the same manner as if these were arguments to printf(), 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:

A panic condition.
A condition that should be corrected immediately, such as a corrupted system database.
Critical conditions, such as hard device errors.
Warning messages.
Conditions that are not error conditions, but that may require special handling.
Informational messages.
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:

Messages generated by random processes. This is the default facility identifier if none is specified.
Reserved for local use.
Reserved for local use.
Reserved for local use.
Reserved for local use.
Reserved for local use.
Reserved for local use.
Reserved for local use.
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 constructed by a bitwise-inclusive OR of zero or more of the following:

Log the process ID with each message. This is useful for identifying specific processes.
Write messages to the system console if they cannot be sent to the logging facility. The syslog() function ensures that the process does not acquire the console as a controlling terminal in the process of writing the message.
Open the connection to the logging facility 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.
Delay open until syslog() is called.
Do not wait for child processes that may have been created during the course of logging the message. 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 argument encodes a default facility to be assigned to all messages that do not have an explicit facility 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 default log mask allows all priorities to be logged. A call to openlog is not required prior to calling setlogmask().

Symbolic constants for use as values of the logopt, facility, priority, and maskpri arguments are defined in the <syslog.h> header.


The setlogmask() function returns the previous log priority mask. The closelog(), openlog() and syslog() functions return no value.


No errors are defined.








printf(), <syslog.h>.

UNIX ® is a registered Trademark of The Open Group.
Copyright © 1997 The Open Group
[ Main Index | XSH | XCU | XBD | XCURSES | XNS ]