How can I monitor a whole directory tree for changes in Linux (ext3 file system)?
Currently the directory contains about half a million files in about 3,000 subdirectories, organized in three directory levels.
Those are mostly small files (< 1kb, some few up to 100 kb). It's a sort of queue and I need to know when files are being created, deleted or their content modified within 5-10 seconds of that happening.
I know there is inotify and sorts, but AFAIK they only monitor a single directory, which means I would need 3,000 inotify handles in my case - more than the usual 1024 handles allowed for a single process. Or am I wrong?
In case the Linux system can't tell me what I need: perhaps there is a FUSE project that simulates a file system (replicating all file accesses on a real file system) and separately logs all modifications (couldn't fine one)?
To my knowledge, there's no other way than recursively setting an inotify watch on each directory.
That said, you won't run out of file descriptors because inotify does not have to reserve an fd to watch a file or a directory (its predecessor, dnotify, did suffer from this limitation). inotify uses "watch descriptors" instead.
According to the documentation for inotifywatch, the default limit is 8192 watch descriptors, and you can increase it by writing the new value to /proc/sys/fs/inotify/max_user_watches.