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SYSLOG(3) BSD Library Functions Manual SYSLOG(3)
NAME
closelog, openlog, setlogmask, syslog, vsyslog -- control system log
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#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, ...);
#include <syslog.h>
#include <stdarg.h>
void
vsyslog(int priority, const char *message, va_list args);
DESCRIPTION
The syslog() function writes 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.
Newlines and other non-printable characters embedded in the message
string are printed in an alternate format. This prevents someone from
using non-printable characters to construct misleading log messages in an
output file. Newlines are printed as "\n", tabs are printed as "\t".
Other control characters are printed using a caret ("^") representation,
for example "^M" for carriage return.
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 priority. Priorities are encoded as a
facility and a level. The facility describes the part of the system gen-erating generating
erating 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 possi-bly possibly
bly 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 parameter ident is a string
that will be prepended to every message. The 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 identify-ing identifying
ing instantiations of daemons.
The facility parameter 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_CRON The cron daemon: cron(8).
LOG_DAEMON System daemons, such as routed(8), that are not provided
for explicitly by other facilities.
LOG_FTP The file transfer protocol daemons: ftpd(8), tftpd(8).
LOG_KERN Messages generated by the kernel. These cannot be gener-ated generated
ated by any user processes.
LOG_LPR The line printer spooling system: lpr(1), lpc(8), lpd(8),
etc.
LOG_MAIL The mail system.
LOG_NEWS The network news system.
LOG_SECURITY Security subsystems, such as ipfw(4).
LOG_SYSLOG Messages generated internally by syslogd(8).
LOG_USER 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 maskpri and
returns the previous mask. Calls to syslog() with a priority not set in
maskpri are rejected. The mask for an individual priority pri is calcu-lated calculated
lated by the macro LOG_MASK(pri); the mask for all priorities up to and
including 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.
EXAMPLES
syslog(LOG_ALERT, "who: internal error 23");
openlog("ftpd", LOG_PID | LOG_NDELAY, LOG_FTP);
setlogmask(LOG_UPTO(LOG_ERR));
syslog(LOG_INFO, "Connection from host %d", CallingHost);
syslog(LOG_INFO|LOG_LOCAL2, "foobar error: %m");
LEGACY SYNOPSIS
#include <syslog.h>
#include <stdarg.h>
These include files are necessary for all functions.
SEE ALSO
logger(1), compat(5), syslogd(8)
HISTORY
These functions appeared in 4.2BSD.
BUGS
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().
Always use the proper secure idiom:
syslog(LOG_ERR, %s, string);
BSD June 4, 1993 BSD
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