Log the given text message via syslog(3). Please note that log messages are committed to the log verbatim --- printf()-style text formatting features offered by the underlying system function are not available. If your log message reads "%s", then that string is exactly what will be written to the log. Also, log messages cannot contain \0 bytes. If they do, all content following that byte will be cut off because the C function assumes that the string ends there.

The Haskell String type can be easily logged with withCStringLen:

 withCStringLen "Hello, world." $ syslog (Just User) Info

ByteStrings can be logged in the same way with the unsafeUseAsCStringLen function from Data.ByteString.Unsafe, which extracts a CStringLen from the ByteString in constant time (no copying!).

Log messages are prioritized with one of the following levels:

>>> [minBound..maxBound] :: [Priority]
[Emergency,Alert,Critical,Error,Warning,Notice,Info,Debug]

The Ord instance for Priority considers the more urgent level lower than less urgent ones:

>>> Emergency < Debug
True
>>> minimum [minBound..maxBound] :: Priority
Emergency
>>> maximum [minBound..maxBound] :: Priority
Debug

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

This function configures the process-wide hidden state of the system's syslog engine. It's probably a bad idea to call this function anywhere except at the very top of your program's main function. And even then you should probably prefer withSyslog instead, which guarantees that syslog is properly initialized within its scope.

Release all syslog-related resources.

Run the given IO a computation within an initialized syslogging scope. The definition is:

  withSyslog ident opts facil f =
    withCString ident $ ptr ->
      bracket_ (openlog ptr opts facil) closelog f

Configure a process-wide filter that determines which logging priorities are ignored and which ones are forwarded to the syslog implementation. For example, use setlogmask [Emergency .. Info] to filter out all debug-level messages from the message stream. Calling setlogmask [minBound..maxBound] enables everything. The special case setlogmask [] does nothing, i.e. the current filter configuration is not modified. This can be used to retrieve the current configuration.

The function openlog allows one to configure a handful of process-wide options that modify the behavior of the syslog function. These options are pid, cons, odelay, and ndelay.