I'm trying to install kaa(IOT platform) on installing the dependencies getting an error on executing the command-

$ sudo systemctl start mongodb
error- Failed to start mongodb.service: Unit mongodb.service is masked.

2 Answers 2


Unit mongodb.service is masked.

So unmask it:

sudo systemctl unmask mongodb

Why are some systemd services in the "masked" state? explains masking.

  • 4
    I also received this error after installing mongodb-org. Why was it masked by default? What does that mean to be masked?
    – Cerin
    Feb 6, 2018 at 18:24
  • sorry. no it does not, is UNMASKS the service file. where do you see an "rm" in this command? Please read up on what masks/unmasks means And the topic starter agrees with me ;-)
    – Rinzwind
    Jun 26, 2019 at 12:12
  • Just another stupid systemd "feature". Systemd is full of charming "surprises". Like PrivateTmp, which silently writes things you intend to go into /tmp into some "magic" directory in Never-Never Land...
    – paulsm4
    Oct 17, 2019 at 18:24

With 3+ version of mongodb. You dont have to start mongodb but you just have to start mongod. So proper way to start mongod will be

sudo systemctl start mongod

  • 5
    Failed to start mongod.service: Unit mongod.service not found. Change mongod to mongodb and hte result is Failed to start mongodb.service: Unit mongodb.service is masked. Jun 10, 2018 at 17:06
  • Yup. By default, you still have to "unmask" it: sudo systemctl unmask mongodb. Silly, silly, silly. But at least it's documented. Sort of...
    – paulsm4
    Oct 17, 2019 at 18:28

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