kazulog@sv1:~$ cat ino_test.sh
#!/bin/bash
# 監視を3つ起動して、それぞれ作成できたかを表示する
for i in 1 2 3; do
  inotifywait -q -m /tmp > /dev/null 2>/tmp/ino$i.err &
  sleep 1
  if [ -s /tmp/ino$i.err ]; then echo "watcher $i: $(head -1 /tmp/ino$i.err)"; else echo "watcher $i: OK"; fi
done
sleep 1; pkill -f "inotifywait -q -m /tmp"; rm -f /tmp/ino*.err
kazulog@sv1:~$ sysctl fs.inotify.max_user_instances
fs.inotify.max_user_instances = 128
kazulog@sv1:~$ sudo sysctl -w fs.inotify.max_user_instances=2
fs.inotify.max_user_instances = 2
kazulog@sv1:~$ ./ino_test.sh
watcher 1: Couldn't initialize inotify: Too many open files
watcher 2: Couldn't initialize inotify: Too many open files
watcher 3: Couldn't initialize inotify: Too many open files
kazulog@sv1:~$ sudo sysctl -w fs.inotify.max_user_instances=128
fs.inotify.max_user_instances = 128
kazulog@sv1:~$ ./ino_test.sh
watcher 1: OK
watcher 2: OK
watcher 3: OK