Hi there,

in this small post we are going to see how systemd works and what are the difference from the old init.d system.

A problem I recently had to solve was a mongodb instance which was starting with the wrong arguments. To debug it I used the following commands:

vdo@ubuntu:/lib/systemd/system$ systemctl status mongod.service 
- mongod.service - High-performance, schema-free document-oriented database
   Loaded: loaded (/lib/systemd/system/mongod.service; enabled; vendor preset: enabled)
   Active: failed (Result: exit-code) since Fri 2016-11-04 14:24:21 CET; 3 days ago
 Main PID: 2870 (code=exited, status=100)

vdo@ubuntu:/lib/systemd/system$ systemctl status mongodb
- mongodb.service - LSB: An object/document-oriented database
   Loaded: loaded (/etc/init.d/mongodb; bad; vendor preset: enabled)
   Active: active (running) since Mon 2016-11-07 15:14:44 CET; 1min 23s ago
  Process: 16456 ExecStop=/etc/init.d/mongodb stop (code=exited, status=0/SUCCESS)
  Process: 16474 ExecStart=/etc/init.d/mongodb start (code=exited, status=0/SUCCESS)
   CGroup: /system.slice/mongodb.service
           +-16486 /usr/bin/mongod --config /etc/mongodb.conf

So basically I had mongod and mongodb. But which was I suppesed to use and how should I start it?

By googling around I found that mongodb was renamed to mongod after version 2.4. Now that I was sure of the version I was supposed to use I could then enable the correct start script. If you have no startup script you can create one follwing this template:

[Unit]
Description=High-performance, schema-free document-oriented database
After=network.target
Documentation=https://docs.mongodb.org/manual

[Service]
User=mongodb
Group=mongodb
ExecStart=/usr/bin/mongod --replSet singleNodeRepl --quiet --config /etc/mongodb.conf

[Install]
WantedBy=multi-user.target

To enable the script:

sudo systemctl enable mongod.service

this command creates a symlink to your service file:

mongod.service -> /lib/systemd/system/mongod.service