SYSLOG(3)
closelog, openlog, syslog - send messages to the system logger
#include
void openlog(const char *ident, int option, int facility);
void syslog(int priority, const char *format, ...);
void closelog(void);
#include
void vsyslog(int priority, const char *format, va_list ap);
closelog() closes the descriptor being used to write to the system logger. optional.
openlog() opens a connection to the system logger for a program.
The string pointed to by ident is prepended to every message, and
is typically set to the program name.
The option argument specifies flags which control the operation of openlog() and subsequent calls to syslog().
The facility argument establishes a default to be used if none is specified in subsequent calls to syslog().
Values for option and facility are given below.
The use of openlog() is optional; it will automatically be called by syslog() if necessary,
in which case ident will default to NULL.
syslog() generates a log message, which will be distributed by syslogd(8).
The priority argument is formed by ORing the facility and the level values.
The remaining arguments are a format,
as in printf(3) and any arguments required by the format,
except that the two character sequence %m will be replaced by the error message string strerror(errno).
A trailing newline is added when needed.
vsyslog() performs the same task as syslog() with the difference that it takes
a set of arguments which have been obtained using the stdarg(3) variable argument list macros.
PARAMETERS
used to set the values of option, facility, and priority.
option
The option argument to openlog() is an OR of any of these:
LOG_CONS Write directly to system console if there is an error while sending to system logger.
LOG_NDELAY Open the connection immediately (normally, the connection is opened when the first message is logged).
LOG_ODELAY The converse of LOG_NDELAY; opening of the connection is delayed until syslog() is called. (default,
LOG_NOWAIT Don't wait for child processes that may have been created while logging the message.
LOG_PERROR Print to stderr as well.
LOG_PID Include PID with each message.
facility
The facility argument is used to specify what type of program is logging the message.
This lets the configuration file specify that messages from different facilities will be handled differently.
RFC 5424
Numerical Facility
Code
0 kernel messages LOG_KERN
1 user-level messages
2 mail system LOG_MAIL
3 system daemons
4 security/authorization messages
5 messages generated internally by syslogd
6 line printer subsystem LOG_LPR
7 network news subsystem LOG_NEWS USENET news subsystem
8 UUCP subsystem LOG_UUCP
9 clock daemon LOG_CRON (cron and at)
10 security/authorization messages
11 FTP daemon LOG_FTP
12 NTP subsystem
13 log audit
14 log alert
15 clock daemon (note 2)
16 local use 0 (local0)
17 local use 1 (local1)
18 local use 2 (local2)
19 local use 3 (local3)
20 local use 4 (local4)
21 local use 5 (local5)
22 local use 6 (local6)
23 local use 7 (local7)
LOG_AUTH security/authorization messages (DEPRECATED Use LOG_AUTHPRIV instead)
LOG_AUTHPRIV security/authorization messages (private)
LOG_DAEMON system daemons without separate facility value
LOG_KERN
LOG_LOCAL0 through LOG_LOCAL7 for local use
LOG_SYSLOG internally by syslogd
LOG_USER (default) generic user-level messages
apple permits any value for the "Facility" ( man syslogd)
only processes running with UID 0 may log messages with a facility value of "com.apple.system",
or with a value that has "com.apple.system" as a prefix.
Messages logged by non UID 0 processes that use "com.apple.system" as a facility value or prefix
will be saved with the facility value "user".
level
This determines the importance of the message. Order in decreasing importance:
0 LOG_EMERG system is unusable
1 LOG_ALERT action must be taken immediately
2 LOG_CRIT critical
3 LOG_ERR
4 LOG_WARNING
5 LOG_NOTICE normal, but significant, condition
6 LOG_INFO
7 LOG_DEBUG
"<"Facility*8+sev">"
Example <0> KERN+EM;
The function setlogmask(3) can be used to restrict logging to specified levels only.
The parameter ident in the call of openlog() is probably stored as-is.
if the string it points to is changed, syslog() may start
prepending the changed string, and if the string it points to ceases to
exist, the results are undefined. Most portable is to use a string constant.
Never pass a string with user-supplied data as a format, use
syslog("%s", string);
SEE ALSO
logger(1), setlogmask(3), syslog.conf(5), syslogd(8)