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SYSLOG(3) FreeBSD Library Functions Manual SYSLOG(3) 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); 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 vari- able 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 in- formation. 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 va_start(3). The message is tagged with priority. Priorities are encoded as a facility and a level. The facility describes the part of the system gen- erating the message: 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 gener- ated 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 through LOG_LOCAL7. The level (ORed with the facility) is selected from the following list, ordered by decreasing importance: 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 possi- bly be handled specially. LOG_INFO Informational messages. LOG_DEBUG Messages that contain information normally of use only when debugging a program. 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 reen- trant 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 points to a string that will be prepended to every message; its storage must persist until closelog() or the corresponding closelog_r(). If the content of the string is changed, behaviour is unspecified. 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_ODELAY Delay opening the connection to syslogd(8) until the first message is logged. This is the opposite of LOG_NDELAY and is the default behaviour when neither option is specified. 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 identify- ing instantiations of daemons. 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() func- tion. 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 re- turns the previous mask. Calls to syslog() with a priority not set in maskpri are rejected. The mask for an individual priority pri is calcu- lated 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 al- lows all priorities to be logged, which corresponds to setlogmask(LOG_UPTO(LOG_DEBUG)). The setlogmask_r() function is the reentrant version of setlogmask(). It takes an additional pointer to a syslog_data structure. RETURN VALUES 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 logger(1), syslogd(8) STANDARDS The functions syslog(), openlog(), closelog(), and setlogmask() conform to the X/Open Systems Interfaces option of IEEE Std 1003.1-2008 ("POSIX.1"). The facilities LOG_AUTHPRIV, LOG_FTP, and LOG_SYSLOG, the option LOG_PERROR, and the macro LOG_UPTO() are extensions to that standard. The standard option LOG_NOWAIT is deprecated in OpenBSD and has no ef- fect. HISTORY The functions syslog(), openlog(), and closelog() appeared in 4.2BSD, setlogmask() in 4.3BSD, and vsyslog() in 4.3BSD Net/1. The functions syslog_r(), vsyslog_r(), openlog_r(), closelog_r(), and setlogmask_r() appeared in 386BSD 0.1 and have been available since OpenBSD 3.1. CAVEATS It is important never to pass a string with user-supplied data as a for- mat 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() be- ing not reentrant, only syslog_r() should be used here. For more infor- mation about reentrancy and signal handlers, see signal(3). FreeBSD 13.0 February 5, 2020 FreeBSD 13.0
NAME | SYNOPSIS | DESCRIPTION | RETURN VALUES | EXAMPLES | SEE ALSO | STANDARDS | HISTORY | CAVEATS
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