The hdaemonize package

[Tags: bsd3, library]

Provides two functions that help writing better UNIX daemons, daemonize and serviced: daemonize does what a daemon should do (forking and closing descriptors), while serviced does that and more (syslog interface, PID file writing, start-stop-restart command line handling, dropping privileges).

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Versions0.1, 0.2, 0.3, 0.4, 0.4.1, 0.4.2, 0.4.3, 0.4.4,,,,
Change logNone available
Dependenciesbase (==4.*), extensible-exceptions, filepath, hsyslog, mtl, unix [details]
AuthorAnton Tayanovskyy, Fred Ross
MaintainerFred Ross <madhadron at gmail dot com>
Home page
UploadedFri Mar 29 17:15:30 UTC 2013 by FrederickRoss
DistributionsLTSHaskell:, NixOS:, Stackage:
Downloads2813 total (65 in last 30 days)
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StatusDocs uploaded by user
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Maintainers' corner

For package maintainers and hackage trustees

Readme for hdaemonize-


`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


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
`serviced` function.

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`. Then:

    # 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 `hdaemonize`, and
logged to `/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
Finally, `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.


* 0.4
    * added support for a privileged action before dropping privileges

* 0.3
    * merged with updates by madhadron

* 0.2
    * provided documentation
    * backported to older GHC versions, tested on 6.8.1

* 0.1
    * initial public release


Anton Tayanovskyy <>, bug reports and feature
requests welcome.

The code is originally based on a public posting by
[Andre Nathan](, used by permission.