I recently bought a new iMac and moved all of my files over using Time Machine. The migration went really well overall and within a few hours I had my development machine up and running. After starting an application I’m building I quickly realized that I couldn’t get MongoDB to start. Running the following command resulted in an error about the data/db directory being read-only:
mongod --authI tried every chmod and chown command known to man and woman kind, tried manually changing security in Finder, compared security to my other iMac (they were the same), and tried a bunch of other things as well. But, try as I might I still saw the read-only folder error when trying to start the server….very frustrating. I found a lot of posts with the same issue but they all solved it by changing security on the folder. That wasn’t the problem on my machine.
After doing more research I found out that Catalina added a new volume to the hard drive and creates a special folder where the MongoDB files need to go. The new folder is:
/System/Volumes/DataThe MongoDB files can then go at:
/System/Volumes/Data/data/dbI ran the following commands to install the latest version of MongoDB using Homebrew (see https://github.com/mongodb/homebrew-brew for more details):
brew tap mongodb/brew
brew install mongodb-communityI then went into the MongoDB config file at /usr/local/etc/mongod.conf. Note that it’s possible yours may be located in a different location based on how you installed MongoDB. I changed the dbPath value to the following and copied my existing DB files into the folder:
dbPath: /System/Volumes/Data/data/dbFinally, I made sure my account had the proper access to the folder by running chown (something I had tried many times earlier but on a folder outside of /System/Volumes/Data):
sudo chown -R $USER /System/Volumes/Data/data/dbAfter that I was able to start MongoDB and everything was back to normal. Hopefully this saves someone a few hours – I wasted way too much time on the issue. 🙂
