Which notify to use

depontius · Advocate Joined: 05 May 2004 Posts: 3509

I want to do some notification-driven stuff. There seem to be at least two, possibly three different notification systems in the kernel, each attempting to get better at it. At the moment it appears that the most (in number of different packages) exists for "inotify". Of course that may be a false metric, maybe there's something newer than inotify that isn't old enough to have many packages yet, but is just obviously better.

In my particular case, I'm going to have a fairly extensive directory tree, typically three levels deep, and would prefer to start one notification at the top. By the time you're down near the bottom, there will likely be a few hundred subdirectories that will need monitoring. Principally I'm looking for files to be created or destroyed in one of those bottom-level subdirectories, but it's also possible, though less frequent, that a bottom-level subdirectory will be created, as well as it's contents.

Right now I'd start the job with pyinotify. Would anyone urge me on a different course?
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steveL · Posted: Sat Mar 28, 2015 1:36 am Post subject:

No, I'd just warn you that you can't do recursive notification, ie you have to monitor subdirectories individually (unless pyinotify wraps that for you.)

AFAIK it's inotify nowadays (replacement for older dnotify.) There's fanotify too, but idk what that's about.

depontius · Advocate Joined: 05 May 2004 Posts: 3509

depontius · Advocate Joined: 05 May 2004 Posts: 3509

I've been playing a bit with pyinotify, and apparently it does wrap directory recursion for me.

For test purposes I've hung one notification on a higher-level directory, then went into my CAD tool and started fiddling with a new schematic. I appear to have received all of the expected notification events, with the creation of a blank schematic. I added a few subcircuits and saved, seeing a further set of modification events. The files related to the circuit are two subdirectories below the inotify monitor point.

I wish there were a way to query the number of inotify handles used. Since this appears to be wrapped, it would seem that one call may generate many, and in fact according to what I just did, a dynamic number of monitor points. Obviously /proc/sys/fs/inotify is just a way to set the max, not to monitor usage. I've taken a quick jaunt around /sys and don't see anything relevant.

But at least it's working.
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