Module Inotify

module Inotify: sig .. end
Public interface
Author(s): Ludovic Stordeur, Vincent Hanquez (initial project)

Inotify overview

The Inotify system provides a mechanism for monitoring file system events. Inotify can be used to monitor individual files, or to monitor directories. When a directory is monitored, Inotify will return events for the directory itself, and for files inside the directory.

Inotify was merged into the 2.6.13 Linux kernel. The required library interfaces were added to glibc in version 2.4.

A quick example

If you are impatient to test this binding, you can cut and paste the following example in your favorite editor then save it under a file named Then, you can compile it with the following command :

$ ocamlfind ocamlc -package onotify -linkpkg -o example

Finally, its execution will monitor all filesystem events which occur directly under the /tmp directory and report them on the standard output.

    (* Make this example more readable. *)
    open Inotify

    (* Initialize a new Inotify instance and get a file descriptor on it. *)
    let fd = init ()

    (* Request for monitoring all event types under "/tmp".
       The returned watch descriptor is unused in this example. *)

    let wd = add_watch fd "/tmp" [ Inotify.R_All ]

    (* This is a convenience formatting routine to print an event. *)
    let string_of_ev {wd=wd; mask=mask; cookie=cookie; name=name} =
        let mask = String.concat ":" ( string_of_ev_type mask) in
        let name = match name with
            | Some s -> s
            | None   -> "\"\"" in
        Printf.sprintf "wd[%d] mask[%s] cookie[%ld] %s" wd mask cookie name

    (* This example never ends. Send a termination signal to kill it. *)
    let _ =
        while true
            (* Read the file descriptor attached to the Inotify instance.
               This can be a blocking operation, so you can poll the file descriptor
               with a timeout before reading it. *)

            let evs = read fd in

            (* Process all detected events. *)
            List.iter (fun ev -> printf "%s\n%!" (string_of_ev ev)) evs

        (* Close the file descriptor attached to the Inotify instance.
           In this example, this operation is never reached because of the above infinite loop.
           However, this is always a good practice to close file descriptors... ;) *)

        Unix.close fd

The Inotify first step

The first function to call if you wish to use Inotify is init.

val init : unit -> Unix.file_descr
init creates a new Inotify instance and returns a file descriptor referring to this instance. At the end, this descriptor must be closed using Unix.close.

You can perfectly creates several Inotify instance which can be attached different watch points. This can be usefull if you wish, at a given time, to monitor just a subset of all your managed watch points.

Attaching watch points

Once you have an Inotify instance. You can attach it some watch points using add_watch. This function takes a list of event types you wish to monitor for this watch point.

add_watch returns a watch descriptor associated to this watch point :

type wd = int 

The exhaustive event type list that add_watch can receive is given here :

type ev_type_req =
| R_Access (*Read access to the file*)
| R_Attrib (*Metadata modification*)
| R_Close_write (*Write-opened file closed*)
| R_Close_nowrite (*Non write-opened file closed*)
| R_Create (*File created under the watched directory*)
| R_Delete (*File deleted under the watched directory*)
| R_Delete_self (*Watched file deleted*)
| R_Modify (*File modified*)
| R_Move_self (*Watched file moved*)
| R_Moved_from (*File moved outside of the watched directory*)
| R_Moved_to (*File moved inside the watched directory*)
| R_Open (*File opened*)
| R_All (*All ABOVE events*)
| R_Move (*Moved_from and Moved_to events*)
| R_Close (*Close_write and Close_nowrite events*)
| R_Dont_follow (*Do not dereference watched file if it is a symbolic link*)
| R_Mask_add (*Add events to (instead of replacing) existing ones*)
| R_Oneshot (*Watch the file until the first event*)
| R_Onlydir (*Watch the file only if it is a directory*)
val add_watch : Unix.file_descr -> string -> ev_type_req list -> wd
add_watch fd inode events attaches a new watch point to the instance fd, monitoring for events on inode. It returns a watch descriptor on this watch point.

Monitoring for events on an Inotify instance

The monitoring of an Inotify instance is performed by reading the file descriptor attached to this instance, using the function read. This function is blocking until some events occur on one or several watch points bound to the instance.

read returns a list of events, each of them related to a watch point. Each event contains the list of event types which have occured.

The exhaustive event type list that an event can contain is given here :

type ev_type =
| Access (*Read access to the file*)
| Attrib (*Metadata modification*)
| Close_write (*Write-opened file closed*)
| Close_nowrite (*Non write-opened file closed*)
| Create (*File created under the watched directory*)
| Delete (*File deleted under the watched directory*)
| Delete_self (*Watched file deleted*)
| Modify (*File modified*)
| Move_self (*Watched file moved*)
| Moved_from (*File moved outside of the watched directory*)
| Moved_to (*File moved inside the watched directory*)
| Open (*File opened*)
| Ignored (*The watched file has been removed explicity (rm_watch()) or automatically (file deleted or filesystem unmounted)*)
| Isdir (*Event subject is a directory*)
| Q_overflow (*Event queue overloaded*)
| Unmount (*Filesystem containing the watched file has been unmounted*)

The definition of an event related to a watch point is given here :

type ev = {
   wd : wd; (*The associated watch descriptor*)
   mask : ev_type list; (*List of received events*)
   cookie : int32; (*Unique identifier used to bind events together. Currently only used to bind Move_from and Move_to*)
   name : string option; (*Optional name associated to the event*)

val read : Unix.file_descr -> ev list
read fd reads for events associated to the descriptor fd and returns a list of events. If there is no pending event when calling this function, read blocks until some event occur.

Other functions

val rm_watch : Unix.file_descr -> wd -> unit
rm_watch fd wd removes wd from the set of watch points associated to fd.
val string_of_ev_type : ev_type -> string
string_of_ev_type ev_type returns the string representation of ev_type.