SYSLOG(3) | Library Functions Manual | SYSLOG(3) |
syslog
, syslog_r
,
vsyslog
, vsyslog_r
,
openlog
, openlog_r
,
closelog
, closelog_r
,
setlogmask
, setlogmask_r
— control system log
#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);
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
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:
LOG_AUTH
LOG_AUTHPRIV
LOG_AUTH
, but logged to a file
readable only by selected individuals.LOG_CRON
LOG_DAEMON
LOG_FTP
LOG_KERN
LOG_LPR
LOG_MAIL
LOG_NEWS
LOG_SYSLOG
LOG_USER
LOG_UUCP
LOG_LOCAL0
LOG_LOCAL1
through LOG_LOCAL7
.The level (ORed with the facility) is selected from the following ordered (high to low) list:
LOG_EMERG
LOG_ALERT
LOG_CRIT
LOG_ERR
LOG_WARNING
LOG_NOTICE
LOG_INFO
LOG_DEBUG
The
vsyslog_r
()
function 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
syslog
() cannot pass the message to
syslogd(8) it will attempt
to write the message to the console
(/dev/console).LOG_NDELAY
LOG_ODELAY
LOG_NDELAY
and is the default behaviour when
neither option is specified.LOG_PERROR
LOG_PID
The facility parameter encodes a default facility to be assigned to all messages that do not have an explicit facility encoded.
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.
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.
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");
These functions appeared in 4.2BSD. The reentrant functions appeared in OpenBSD 3.1.
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).
July 10, 2014 | OpenBSD-5.6 |