NAME
closelog, openlog, syslog - send messages to the system logger
SYNOPSIS
#include <syslog.h>
I void openlog(const char * ident , int option , int facility );
I void syslog(int priority , const char * format , ...);
I void closelog(void);
#define _BSD_SOURCE
#include <stdarg.h>
I void vsyslog(int priority , const char * format , va_list ap );
DESCRIPTION
R closelog ()
closes the descriptor being used to write to the system logger.
The use of
R closelog ()
is optional.
R openlog ()
opens a connection to the system logger for a program.
The string pointed to by
ident
is prepended to every message, and is typically set to the program name.
The
option
argument specifies flags which control the operation of
R openlog ()
and subsequent calls to
R syslog ().
The
facility
argument establishes a default to be used if
none is specified in subsequent calls to
R syslog ().
Values for
option
and
facility
are given below.
The use of
R openlog ()
is optional; it will automatically be called by
R syslog ()
if necessary, in which case
ident
will default to NULL.
R syslog ()
generates a log message, which will be distributed by
syslogd(8).
The
priority
argument is formed by ORing the
facility
and the
level
values (explained below).
The remaining arguments
are a
R format ,
as in
printf(3)
and any arguments required by the
R format ,
except that the two character sequence %m will be replaced by
the error message string
R strerror ( errno ).
A trailing newline may be added if needed.
The function
R vsyslog ()
performs the same task as
R syslog ()
with the difference that it takes a set of arguments which have
been obtained using the
stdarg(3)
variable argument list macros.
The subsections below lists the parameters used to set the values of
R option , facility , and priority .
option
The
option
argument to
R openlog ()
is an OR of any of these:
LOG_CONS
Write directly to system console if there is an error while sending to
system logger.
LOG_NDELAY
Open the connection immediately (normally, the connection is opened when
the first message is logged).
LOG_NOWAIT
Don't wait for child processes that may have been created while logging
the message.
(The GNU C library does not create a child process, so this
option has no effect on Linux.)
LOG_ODELAY
The converse of
R LOG_NDELAY ;
opening of the connection is delayed until
R syslog ()
is called.
(This is the default, and need not be specified.)
LOG_PERROR
(Not in POSIX.1-2001.)
Print to stderr as well.
LOG_PID
Include PID with each message.
facility
The
facility
argument is used to specify what type of program is logging the message.
This lets the configuration file specify that messages from different
facilities will be handled differently.
LOG_AUTH
security/authorization messages (DEPRECATED Use
LOG_AUTHPRIV
instead)
LOG_AUTHPRIV
security/authorization messages (private)
LOG_CRON
clock daemon
(cron and at)
LOG_DAEMON
system daemons without separate facility value
R LOG_LOCAL0 through LOG_LOCAL7
reserved for local use
LOG_LPR
line printer subsystem
LOG_NEWS
USENET news subsystem
LOG_SYSLOG
messages generated internally by
syslogd(8)
R LOG_USER (default)
generic user-level messages
LOG_UUCP
UUCP subsystem
level
This determines the importance of the message.
The levels are, in order of decreasing importance:
LOG_EMERG
system is unusable
LOG_ALERT
action must be taken immediately
LOG_CRIT
critical conditions
LOG_WARNING
warning conditions
LOG_NOTICE
normal, but significant, condition
LOG_INFO
informational message
LOG_DEBUG
debug-level message
The function
setlogmask(3)
can be used to restrict logging to specified levels only.
CONFORMING TO
The functions
R openlog (),
R closelog (),
and
R syslog ()
(but not
R vsyslog ())
are specified in SUSv2 and POSIX.1-2001.
POSIX.1-2001 specifies only the
LOG_USER
and
R LOG_LOCAL*
values for
R facility .
However, with the exception of
R LOG_AUTHPRIV
and
R LOG_FTP ,
the other
facility
values appear on most Unix systems.
The
LOG_PERROR
value for
option
is not specified by POSIX.1-2001, but is available
in most versions of Unix.
NOTES
The parameter
ident
in the call of
R openlog ()
is probably stored as-is.
Thus, if the string it points to
is changed,
R syslog ()
may start prepending the changed string, and if the string
it points to ceases to exist, the results are undefined.
Most portable is to use a string constant.
Never pass a string with user-supplied data as a format,
the following instead:
syslog(priority, "%s", string);
SEE ALSO
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