The
syslog ();
function
writes
Fa message
to the system message logger.
The message is then written to the system console, log files,
logged-in users, or forwarded to other machines as appropriate.
(See
syslogd(8).)
The message is identical to a
printf(3)
format string, except that
`%m'
is replaced by the current error
message.
(As denoted by the global variable
errno
see
strerror(3).)
A trailing newline is added if none is present.
The
vsyslog ();
function
is an alternate form in which the arguments have already been captured
using the variable-length argument facilities of
stdarg(3).
The message is tagged with
Fa priority .
Priorities are encoded as a
Fa facility
and a
level
The facility describes the part of the system
generating the message.
The level is selected from the following
ordered
(high to low) list:
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, e.g., hard device errors.
LOG_ERR
Errors.
LOG_WARNING
Warning messages.
LOG_NOTICE
Conditions that are not error conditions,
but should possibly be handled specially.
LOG_INFO
Informational messages.
LOG_DEBUG
Messages that contain information
normally of use only when debugging a program.
The
openlog ();
function
provides for more specialized processing of the messages sent
by
syslog ();
and
vsyslog (.);
The
Fa ident
argument
is a string that will be prepended to every message.
The
Fa logopt
argument
is a bit field specifying logging options, which is formed by
OR 'ing
one or more of the following values:
LOG_CONS
If
syslog ();
cannot pass the message to
syslogd(8)
it will attempt to write the message to the console
(``/dev/console
''
)
LOG_NDELAY
Open the connection to
syslogd(8)
immediately.
Normally the open is delayed until the first message is logged.
Useful for programs that need to manage the order in which file
descriptors are allocated.
LOG_PERROR
Write the message to standard error output as well to the system log.
LOG_PID
Log the process id with each message: useful for identifying
instantiations of daemons.
The
Fa facility
argument encodes a default facility to be assigned to all messages
that do not have an explicit facility encoded:
LOG_AUTH
The authorization system:
login(1),
su(1),
getty(8),
etc.
LOG_AUTHPRIV
The same as
LOG_AUTH
but logged to a file readable only by
selected individuals.
LOG_CONSOLE
Messages written to
/dev/console
by the kernel console output driver.
Messages generated by random user processes.
This is the default facility identifier if none is specified.
LOG_UUCP
The uucp system.
LOG_LOCAL0
Reserved for local use.
Similarly for
LOG_LOCAL1
through
LOG_LOCAL7
The
closelog ();
function
can be used to close the log file.
The
setlogmask ();
function
sets the log priority mask to
Fa maskpri
and returns the previous mask.
Calls to
syslog ();
with a priority not set in
Fa maskpri
are rejected.
The mask for an individual priority
Fa pri
is calculated by the macro
LOG_MASK (pri ;);
the mask for all priorities up to and including
Fa toppri
is given by the macro
LOG_UPTO (toppri ; .);
The default allows all priorities to be logged.
RETURN VALUES
The routines
closelog (,);
openlog (,);
syslog ();
and
vsyslog ();
return no value.
The routine
setlogmask ();
always returns the previous log mask level.
Never pass a string with user-supplied data as a format without using
`%s'
An attacker can put format specifiers in the string to mangle your stack,
leading to a possible security hole.
This holds true even if the string was built using a function like
snprintf (,);
as the resulting string may still contain user-supplied conversion specifiers
for later interpolation by
syslog (.);
