NAME
syslog
, syslog_r
,
vsyslog
, vsyslog_r
,
syslogp
, syslogp_r
,
vsyslogp
, vsyslogp_r
,
openlog
, openlog_r
,
closelog
, closelog_r
,
setlogmask
, setlogmask_r
— control system log
LIBRARY
library “libc”
SYNOPSIS
#include
<syslog.h>
void
syslog
(int
priority, const char
*message, ...);
void
syslog_r
(int
priority, struct
syslog_data *data, const
char *message,
...);
void
syslogp
(int
priority, const char
*msgid, const char
*sdfmt, const char
*message, ...);
void
syslogp_r
(int
priority, struct
syslog_data *data, const
char *msgid, const char
*sdfmt, const char
*message, ...);
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);
#include
<stdarg.h>
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
vsyslogp
(int
priority, const char
*msgid, const char
*sdfmt, const char
*message, va_list
args);
void
vsyslogp_r
(int
priority, struct
syslog_data *data, const
char *msgid, const char
*sdfmt, const char
*message, va_list
args);
DESCRIPTION
Thesyslog
()
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 multithread-safe 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 and the
SYSLOG_DATA_INIT
constant are defined as:
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 { \ .log_file = -1, \ .log_fac = LOG_USER, \ .log_mask = 0xff, \ }
The 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 alternative form in which the arguments have already been
captured using the variable-length argument facilities of
stdarg(3).
The
syslogp
()
variants take additional arguments which correspond to new fields in the
syslog-protocol message format. All three arguments are evaluated as
printf(3) format strings and any of them can be
NULL
. This enables applications to use message IDs,
structured data, and UTF-8 encoded content in messages.
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 multithread-safe 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.
LOG_NLOG
- Stops syslog from writing to the system log. Only useful with
LOG_PERROR
. 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. (This PID is placed within brackets between the ident and the message.)
LOG_PTRIM
- Trim anything syslog added to the message before writing to standard error output.
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 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 multithread-safe 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 multithread-safe functions.
The
closelog
()
function can be used to close the log file.
The
closelog_r
()
does the same thing as
closelog(3) but in a multithread-safe 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 multithread-safe version of
setlogmask
(). It takes an additional pointer to a
syslog_data structure.
RETURN VALUES
The routines closelog
(),
closelog_r
(), openlog
(),
openlog_r
(), syslog
(),
syslog_r
(), vsyslog
(),
vsyslog_r
(), syslogp
(),
syslogp_r
(), vsyslogp
(), and
vsyslogp_r
() 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"); syslogp(LOG_INFO|LOG_LOCAL2, NULL, NULL, "foobar error: %m"); syslogp(LOG_INFO, "ID%d", "[meta language=\"en-US\"]", "event: %s", 42, EventDescription);
For the multithread-safe functions:
struct syslog_data sdata = SYSLOG_DATA_INIT; syslog_r(LOG_INFO|LOG_LOCAL2, &sdata, "foobar error: %m");
SEE ALSO
The BSD syslog Protocol, RFC, 3164, August 2001.
The syslog Protocol, Internet-Draft, draft-ietf-syslog-protocol-23, September 2007.
HISTORY
These non-multithread-safe functions appeared in 4.2BSD. The multithread-safe functions appeared in OpenBSD 3.1 and then in NetBSD 4.0. The async-signal-safe functions appeared in NetBSD 4.0. The syslog-protocol functions appeared in NetBSD 5.0.
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 your stack,
leading to a possible security hole. This holds true even if you have built
the string “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);
With syslogp
() the caller is responsible
to use the right formatting for the message fields. A
msgid must only contain up to 32 ASCII characters. A
sdfmt has strict rules for parenthesis and character
quoting. If the msgfmt contains UTF-8 characters, then
it has to start with a Byte Order Mark.