|SYSLOG(3)||Linux Programmer's Manual||SYSLOG(3)|
void openlog(const char *ident, int option, int facility); void syslog(int priority, const char *format, ...); void closelog(void);
void vsyslog(int priority, const char *format, va_list ap);
Since glibc 2.19: _DEFAULT_SOURCE Glibc 2.19 and earlier: _BSD_SOURCE
The string pointed to by ident is prepended to every message, and is typically set to the program name. If ident is NULL, the program name is used. (POSIX.1-2008 does not specify the behavior when ident is NULL.)
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(). The values that may be specified for option and facility are described below.
The use of openlog() is optional; it will automatically be called by syslog() if necessary, in which case ident will default to NULL.
The priority argument is formed by ORing together a facility value and a level value (described below). If no facility value is ORed into priority, then the default value set by openlog() is used, or, if there was no preceding openlog() call, a default of LOG_USER is employed.
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). The format string need not include a terminating newline character.
The function 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.
- Write directly to the system console if there is an error while sending to the system logger.
- Open the connection immediately (normally, the connection is opened when the first message is logged). This may be useful, for example, if a subsequent chroot(2) would make the pathname used internally by the logging facility unreachable.
- Don't wait for child processes that may have been created while logging the message. (The GNU C library does not create a child process, so this option has no effect on Linux.)
- The converse of LOG_NDELAY; opening of the connection is delayed until syslog() is called. (This is the default, and need not be specified.)
- (Not in POSIX.1-2001 or POSIX.1-2008.) Also log the message to stderr.
- Include the caller's PID with each message.
- security/authorization messages
- security/authorization messages (private)
- clock daemon (cron and at)
- system daemons without separate facility value
- ftp daemon
- kernel messages (these can't be generated from user processes)
- LOG_LOCAL0 through LOG_LOCAL7
- reserved for local use
- line printer subsystem
- mail subsystem
- USENET news subsystem
- messages generated internally by syslogd(8)
- LOG_USER (default)
- generic user-level messages
- UUCP subsystem
- system is unusable
- action must be taken immediately
- critical conditions
- error conditions
- warning conditions
- normal, but significant, condition
- informational message
- debug-level message
The function setlogmask(3) can be used to restrict logging to specified levels only.
|openlog (), closelog ()||Thread safety||MT-Safe|
|syslog (), vsyslog ()||Thread safety||MT-Safe env locale|
POSIX.1-2001 specifies only the LOG_USER and LOG_LOCAL* values for facility. However, with the exception of LOG_AUTHPRIV and LOG_FTP, the other facility values appear on most UNIX systems.
The LOG_PERROR value for option is not specified by POSIX.1-2001 or POSIX.1-2008, but is available in most versions of UNIX.
Never pass a string with user-supplied data as a format, use the following instead:
syslog(priority, "%s", string);