This module provides support for daemonizing a process. It provides flexibility as to where the standard file descriptors (stdin, stdout and stderr) are connected after daemonization has occurred.
module Fd_redirection : sig .. end
type t = [ `Dev_null
| `Do_not_redirect
| `File_append of string
| `File_truncate of string ]
val daemonize : ?redirect_stdout:Fd_redirection.t ->
?redirect_stderr:Fd_redirection.t -> ?cd:string -> ?umask:int -> unit -> unit
daemonize makes the executing process a daemon.

See Chapter 13 of Advanced Programming in the UNIX Environment Second Edition by Stephens and Rago for more details.

The optional arguments have defaults as per daemonize_wait, below.

By default, output sent to stdout and stderr after daemonization will be silently eaten. This behaviour may be adjusted by using redirect_stdout and redirect_stderr. See the documentation for daemonize_wait below.

Raises Failure if fork was unsuccessful.
val daemonize_wait : ?redirect_stdout:Fd_redirection.t ->
?redirect_stderr:Fd_redirection.t ->
?cd:string -> ?umask:int -> unit -> (unit -> unit) Staged.t
daemonize_wait makes the executing process a daemon, but delays full detachment from the calling shell/process until the returned "release" closure is called.

Any output to stdout/stderr before the "release" closure is called will get sent out normally. After "release" is called, stdin is connected to /dev/null, and stdout and stderr are connected as specified by redirect_stdout and redirect_stderr. The default is the usual behaviour whereby both of these descriptors are connected to /dev/null.

Note that calling release will adjust SIGPIPE handling, so you should not rely on the delivery of this signal during this time.

daemonize_wait allows you to daemonize and then start async, but still have stdout/stderr go to the controlling terminal during startup. By default, when you daemonize, toplevel exceptions during startup would get sent to /dev/null. With daemonize_wait, toplevel exceptions can go to the terminal until you call release.

Raises Failure if fork was unsuccessful.