closelog()
closes the descriptor being used to write to the system logger.
The use of
closelog()
is optional.
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
openlog()
and subsequent calls to
syslog().
The
facility
argument establishes a default to be used if
none is specified in subsequent calls to
syslog().
Values for
option
and
facility
are given below.
The use of
openlog()
is optional; it will automatically be called by
syslog()
if necessary, in which case
ident
will default to NULL.
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
format,
as in
printf(3)
and any arguments required by the
format,
except that the two character sequence
%m
will be replaced by
the error message string
strerror(errno).
A trailing newline may be added if needed.
The function
vsyslog()
performs the same task as
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 list the parameters used to set the values of
option, facility, and priority.
option
The
option
argument to
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
LOG_NDELAY;
opening of the connection is delayed until
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
LOG_FTP
ftp daemon
LOG_KERN
kernel messages (these can't be generage from user processes)
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_ERR
error 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
openlog(),
closelog(),
and
syslog()
(but not
vsyslog())
are specified in SUSv2 and POSIX.1-2001.
POSIX.1-2001 specifies only the
LOG_USER
and
LOG_LOCAL*
values for
facility.
However, with the exception of
LOG_AUTHPRIV
and
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 argument
ident
in the call of
openlog()
is probably stored as-is.
Thus, if the string it points to
is changed,
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,
use the following instead:
This page is part of release 3.14 of the Linux
man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
http://www.kernel.org/doc/man-pages/.
