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inotify

Control the maximum number of watchers.

inotify watcher count limit

Check current limits:

$ sysctl fs.inotify
fs.inotify.max_queued_events = 16384
fs.inotify.max_user_instances = 128
fs.inotify.max_user_watches = 409600

Count opened files:

lsof | grep inotify | wc -l

Increase the limit:

echo fs.inotify.max_user_watches=524288 | 
  sudo tee /etc/sysctl.d/40-max-user-watches.conf && 
  sudo sysctl --system

echo "fs.inotify.max_user_watches=409600" | sudo tee -a /etc/sysctl.conf

Check who's using them all:

$ bin/inotify-consumers 

   INOTIFY   INSTANCES
   WATCHES      PER   
    COUNT     PROCESS   PID USER         COMMAND
------------------------------------------------------------
   26730         1        2815 m           /usr/bin/syncthing serve --no-browser --logfile=default
    5374         1        3900 m           /usr/libexec/tracker-miner-fs-3
<snip>
   35051  WATCHES TOTAL COUNT

INotify instances per user (e.g. limits specified by fs.inotify.max_user_instances): 

INSTANCES    USER
-----------  ------------------
65           m

/proc interfaces

     The following interfaces can be used to limit the amount of
     kernel memory consumed by inotify:

     /proc/sys/fs/inotify/max_queued_events
            The value in this file is used when an application calls
            inotify_init(2) to set an upper limit on the number of
            events that can be queued to the corresponding inotify
            instance.  Events in excess of this limit are dropped, but
            an IN_Q_OVERFLOW event is always generated.

     /proc/sys/fs/inotify/max_user_instances
            This specifies an upper limit on the number of inotify
            instances that can be created per real user ID.

     /proc/sys/fs/inotify/max_user_watches
            This specifies an upper limit on the number of watches
            that can be created per real user ID.