ERROR: Failed to allocate directory watch: Too many open files

解决办法：

systemctl start core-daemon.service
    Failed to allocate directory watch: Too many open files
    Job forr core-daemon.service failed because the service did not take the steps required by its unit configuration.
    See "systemctl  status core-daemon.service" and "journalctl  -xe" forr details.

sysctl fs.inotify.max_user_instances=512