Increase max number of open files of mongodb on Ubuntu with systemd

You can increase the maximum number of open files of a processs spawn by systemd by editing its config file, for example, /lib/systemd/system/mongod.service.

But it’d be better to use drop-in file. In this case, create a directory in /etc/systemd/system based on the service name, and put a configuration file in it.

For mongodb, you can create /etc/systemd/system/mongod.service.d/nofile.conf (the filename itself doesn’t matter, but it should have .conf extension), and put the following line to increase the number of open files.

[Service]
LimitNOFILE=1006500

You need to make systemd reload configuration files by sudo systemctl daemon-reload, then restart the service by sudo systemctl restart mongod.

Use systemctl status mongod to check if this configuration was applied properly.

systemctl status mongod
● mongod.service - MongoDB Database Server
   Loaded: loaded (/lib/systemd/system/mongod.service; enabled; vendor preset: e
  Drop-In: /etc/systemd/system/mongod.service.d
           └─nofile.conf
   Active: active (running) since Sun 2020-07-12 23:09:14 UTC; 23h ago
     Docs: https://docs.mongodb.org/manual
 Main PID: 32120 (mongod)
   CGroup: /system.slice/mongod.service
           └─32120 /usr/bin/mongod --config /etc/mongod.conf

Jul 12 23:09:14 ip-10-0-11-10 systemd[1]: Started MongoDB Database Server.