Log messages have a priority attached.

Syslog distinguishes various system facilities. Most applications should log in USER.

withSyslog options for the syslog service.

withSyslog options for the priority mask

A practical default syslog config. You'll at least want to change the identifier.

Bracket an IO computation between calls to _openlog, _setlogmask, and _closelog, and provide a logging function which can be used as follows:

main = withSyslog defaultConfig $ \syslog -> do
         putStrLn "huhu"
         syslog [Debug] "huhu"

Note that these are process-wide settings, so multiple calls to this function will interfere with each other in unpredictable ways.

The type of logging function provided by withSyslog.

Like withSyslog but provides a function for logging to specific facilities per message rather than the default facilities in your SyslogConfig.

The type of function provided by withSyslogTo.

Open a connection to the system logger for a program. The string identifier passed as the first argument is prepended to every message, and is typically set to the program name. The behavior is unspecified by POSIX.1-2008 if that identifier is nullPtr.

Close the descriptor being used to write to the system logger.

A process has a log priority mask that determines which calls to syslog may be logged. All other calls will be ignored. Logging is enabled for the priorities that have the corresponding bit set in mask. The initial mask is such that logging is enabled for all priorities. This function sets this logmask for the calling process, and returns the previous mask. If the mask argument is 0, the current logmask is not modified.

Generate a log message, which will be distributed by syslogd(8). The priority argument is formed by ORing the facility and the level values (explained below). 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 may be added if needed.