lwt

Promises, concurrency, and parallelized I/O
Library lwt_unix
Module Lwt_daemon
val daemonize : ?syslog:bool -> ?stdin:[ `Dev_null | `Close | `Keep ] -> ?stdout: [ `Dev_null | `Close | `Keep | `Log_default | `Log of Lwt_log.logger ] -> ?stderr: [ `Dev_null | `Close | `Keep | `Log_default | `Log of Lwt_log.logger ] -> ?directory:string -> ?umask:[ `Keep | `Set of int ] -> unit -> unit

Put the current running process into daemon mode. I.e. it forks and exit the parent, detach it from its controlling terminal, and redict standard intputs/outputs..

Notes:

  • you must be sure that there is no pending threads when calling this function, otherwise they may be canceled.

If syslog is true (the default), then Lwt_log.default is set to Lwt_log.syslog ~facility:`Daemon (), otherwise it is kept unchanged.

stdin is one of:

  • `Dev_null which means that Unix.stdin is reopened as /dev/null, this is the default behavior
  • `Close means that Unix.stdin is simply closed
  • `Keep means that Unix.stdin is left unchanged

stdout and stderr control how the two associated file descriptors are redirected:

  • `Dev_null means that the output is redirected to /dev/null
  • `Close means that the file descriptor is closed
  • `Keep means that it is left unchanged
  • `Log logger means that the output is redirected to this logger
  • `Log_default means that the output is redirected to the default logger

Both stdout and stderr default to `Log_default.

Warning: do not redirect an output to a logger logging into this output. For example, this code will create an infinite loop:

let logger = Lwt_log.channel ~close_mode:`Keep ~channel:Lwt_io.stderr () in
Lwt_daemon.daemonize ~syslog:false ~stderr:(`Log logger) ();
prerr_endline "foo"

The current working directory is set to directory, which defaults to "/".

umask may be one of:

  • `Keep which means that the umask is left unchanged
  • `Set n which means that the umask is set to n

It defaults to `Set 0o022.