hdaemonize is a simple library that hides some of the complexities
of writing UNIX daemons in Haskell.
The latest version is available (BSD license) at GitHub.
The synopsis is:
import System.Posix.Daemonize main = daemonize $ program
This code will make
program do what good daemons should do, that is,
detach from the terminal, close file descriptors, create a new process
group, and so on.
If you want more functionality than that, it is available as a
Here is an example:
import Control.Concurrent import System.Posix.Daemonize loop i log = do threadDelay $ 10^6 log (show i) writeFile "/tmp/counter" $ show i if i == 5 then undefined else loop (i + 1) log main = serviced (loop 0)
Let us say this program is compiled as
# mydaemon start
starts the service. A second call to start will complain that the program is already running.
During its execution, mydaemon will simply write a new number to
/tmp/counter every second, until it reaches 5. Then, an exception
will be thrown. This exception will be caught by
/var/log/daemon.log or similar (this is depends on how
syslog works on your platorm).
log (show i) will leave messages
in the same file.
When the exception is thrown, the program will be restared in 5 seconds, and will start counting from 0 again.
The following commands are also made available:
# mydaemon stop # mydaemon restart
mydaemon drops privileges. By default it changes the
effective user and group ids to those of the
daemon user, but it
prefers to use those of
mydaemon, if present.
- Fix pre-AMP builds.
- Updated to use hsyslog >=4
- added support for a privileged action before dropping privileges
- merged with updates by madhadron
- provided documentation
- backported to older GHC versions, tested on 6.8.1
- initial public release
Anton Tayanovskyy .
The code is originally based on a public posting by Andre Nathan, used by permission.