This module provides a simple interface to creating, checking the status of, and stopping background jobs.

Use runDetached to start a background job. For instance, here is a daemon that peridically hits a webserver:

 import Control.Concurrent
 import Control.Monad
 import Data.Default
 import Data.Maybe
 import Network.BSD
 import Network.HTTP
 import Network.URI
 import System.Posix.Daemon

 main :: IO ()
 main = runDetached (Just "diydns.pid") def $ forever $ do
     hostname <- getHostName
     _ <- simpleHTTP
              (Request { rqURI     = fromJust (parseURI "http://foo.com/dns")
                       , rqMethod  = GET
                       , rqHeaders = []
                       , rqBody    = hostname })
     threadDelay (600 * 1000 * 1000)

To check if the above job is running, use isRunning with the same pidfile:

 isRunning "diydns.pid"

Finally, to stop the above job (maybe because we're rolling a new version of it), use kill:

 kill "diydns.pid"

To stop a job and wait for it to close (and release its pidfile), use killAndWait:

 killAndWait "diydns.pid" >> doSomething

As a side note, the code above is a script that the author uses as a sort of homebrew dynamic DNS: the remote address is a CGI script that records the IP addresses of all incoming requests in separate files named after the contents of the requests; the addresses are then viewable with any browser.