"How do I increase the inotify limit to get my filesystem watcher to work?"

[da5nsy (Danny Garside)]

Hey! New user here, and I’m seeing:

Failed to start filesystem watcher for folder yourLabel (yourID): failed to set up inotify handler. Please increase inotify limits, see https://docs.syncthing.net/users/faq.html#inotify-limits

which from searching this forum seems to be a common site.

I’m a little confused though, because I only have 4 folders.

number of watches per user (usually 8192)

Is it 1 folder = 1 watch? Is it 1 file = 1 watch? How can one find out what the current restriction is?

(Meta: can I add this info to the docs?)

Also, I think (but I’m not sure, how would I know? I refreshed the web-ui and nothing changed, I had to manually re-scan to see new files) that echo 204800 | sudo tee /proc/sys/fs/inotify/max_user_watches didn’t do anything for me, is there a typo in that line, or does that only work for certain systems?

[Nummer378 (Max)]

@da5nsy

(Meta: can I add this info to the docs?)

The docs are open source, anyone can submit contributions to it through GitHub: GitHub - syncthing/docs: Documentation site

@da5nsy

I’m a little confused though, because I only have 4 folders.

number of watches per user (usually 8192)

Is it 1 folder = 1 watch? Is it 1 file = 1 watch?

The docs mean actual filesystem folders, not “syncthing-folders”. The kernel’s inotify system allows a process to watch for events (file changes) on individual files or directories. However, the latter is not recursive so if I have the following directory structure:

example
├── 1
│   └── foobar.txt
├── 2
│   └── myfile.png
└── 3
    └── other_data.bin

4 directories, 3 files

Then that’s 4 watches: Syncthing watches the top-level folder “example” to see if any new folders or files are added at the same level as 1,2,3, but it also watches folders 1, 2 and 3 individually to check if files and folders are added/removed/changed within them.

@da5nsy

How can one find out what the current restriction is?

The current per-user limit should be in the (virtual) file cat /proc/sys/fs/inotify/max_user_watches. If you change the limit, it will take a moment to become effective. Syncthing needs to retry setting up the watches, so either rescan all folders or restart syncthing entirely. Refreshing the GUI does absolutely nothing for syncthing.

[da5nsy (Danny Garside)]

Thank you @Nummer378!

With what you’ve told me, I’m a bit confused as to why I saw the warnings.

I think this status panel is showing me that I have 124 watches. Nowhere near 8192…

I ran curl -s https://raw.githubusercontent.com/fatso83/dotfiles/master/utils/scripts/inotify-consumers | bash from here, to see what else was using watches…

   INOTIFY   INSTANCES
   WATCHES      PER   
    COUNT     PROCESS   PID USER         COMMAND
------------------------------------------------------------
  181260         1      548474 danny       /usr/bin/proton-drive-sync start --no-daemon
   22869         1      390492 danny       /home/danny/.dropbox-dist/dropbox-lnx.x86_64-242.4
     142         1        8498 danny       /usr/bin/syncthing serve --no-browser --logfile=de
...

… and I see that this is not just a system that syncthing uses! That explains it.