NAME
syslog
, syslog_r
,
vsyslog
, vsyslog_r
,
openlog
, openlog_r
,
closelog
, closelog_r
,
setlogmask
, setlogmask_r
— control system log
SYNOPSIS
#include
<syslog.h>
#include <stdarg.h>
void
syslog
(int
priority, const char
*message, ...);
void
syslog_r
(int
priority, struct
syslog_data *data, const
char *message,
...);
void
vsyslog
(int
priority, const char
*message, va_list
args);
void
vsyslog_r
(int
priority, struct
syslog_data *data, const
char *message, va_list
args);
void
openlog
(const
char *ident, int
logopt, int
facility);
void
openlog_r
(const
char *ident, int
logopt, int
facility, struct
syslog_data *data);
void
closelog
(void);
void
closelog_r
(struct
syslog_data *data);
int
setlogmask
(int
maskpri);
int
setlogmask_r
(int
maskpri, struct
syslog_data *data);
struct syslog_data { int log_file; int connected; int opened; int log_stat; const char *log_tag; int log_fac; int log_mask; }; #define SYSLOG_DATA_INIT {-1, 0, 0, 0, NULL, LOG_USER, 0xff}
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.
The
syslog_r
()
function is a reentrant version of the syslog
()
function. It takes a pointer to a syslog_data
structure which is used to store information. This parameter must be
initialized before syslog_r
() is called. The
SYSLOG_DATA_INIT
constant is used for this purpose.
The syslog_data structure is composed of the following
elements:
log_file
- contains the file descriptor of the file where the message is logged
connected
- indicates if connect has been done
opened
- indicates if
openlog_r
() has been called log_stat
- status bits, set by
openlog_r
() log_tag
- string to tag the entry with
log_fac
- facility code
log_mask
- mask of priorities to be logged
The
vsyslog
()
function is an alternate form in which the arguments have already been
captured using the variable-length argument facilities of
varargs(3).
The message is tagged with priority. Priorities are encoded as a 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
vsyslog_r
()
is used the same way as vsyslog
() except that it
takes an additional pointer to a syslog_data
structure. It is a reentrant version of the
vsyslog
() function described above.
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. This option must be used in programs that call chroot(2) where the new root does not have its own log socket.
LOG_PERROR
- Write the message to standard error output as well as to the system log.
LOG_PID
- Log the process ID with each message; useful for identifying 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 dhcpd(8), that are not provided for explicitly by other facilities.
LOG_FTP
- The file transfer protocol daemon, ftpd(8).
LOG_KERN
- Messages generated by the kernel. These cannot be generated 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_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
throughLOG_LOCAL7
.
The
openlog_r
()
function is the reentrant version of the openlog
()
function. It takes an additional pointer to a
syslog_data structure. This function must be used in
conjunction with the other reentrant functions.
The
closelog
()
function can be used to close the log file.
closelog_r
()
does the same thing but in a reentrant way and takes an additional pointer
to a syslog_data structure.
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 calculated 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.
The
setlogmask_r
()
function is the reentrant version of setlogmask
().
It takes an additional pointer to a syslog_data
structure.
RETURN VALUES
The closelog
(),
closelog_r
(), openlog
(),
openlog_r
(), syslog
(),
syslog_r
(), vsyslog
(), and
vsyslog_r
() functions return no value.
The routines setlogmask
() and
setlogmask_r
() always return 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");
For the reentrant functions:
struct syslog_data sdata = SYSLOG_DATA_INIT; syslog_r(LOG_INFO|LOG_LOCAL2, &sdata, "foobar error: %m");
SEE ALSO
HISTORY
These functions appeared in 4.2BSD. The reentrant functions appeared in OpenBSD 3.1.
CAVEATS
It is important never to pass a string with user-supplied data as
a format without using ‘%s
’. An
attacker can put format specifiers in the string to mangle the stack,
leading to a possible security hole. This holds true even if the string has
been built “by hand” using a function like
snprintf
(), as the resulting string may still
contain user-supplied conversion specifiers for later interpolation by
syslog
().
Always be sure to use the proper secure idiom:
syslog(priority, "%s", string);
syslog_r
() and the other reentrant
functions should only be used where reentrancy is required (for instance, in
a signal handler). syslog
() being not reentrant,
only syslog_r
() should be used here. For more
information about reentrancy and signal handlers, see
signal(3).