macos - MongoDB can't find data directory after upgrading to Mac OS 10.15 (Catalina)

Question

I updated to MacOS 10.15 (Catalina) today. When I run mongod in the terminal it cannot find the /data/db directory:

?  /Users/william > mongod
2019-10-08T17:02:44.183+0800 I CONTROL  [main] Automatically disabling TLS 1.0, to force-enable TLS 1.0 specify --sslDisabledProtocols 'none'
2019-10-08T17:02:44.209+0800 I CONTROL  [initandlisten] MongoDB starting : pid=43162 port=27017 dbpath=/data/db 64-bit host=Williams-MacBook-Pro-6.local
2019-10-08T17:02:44.209+0800 I CONTROL  [initandlisten] db version v4.0.3
2019-10-08T17:02:44.209+0800 I CONTROL  [initandlisten] git version: 7ea530946fa7880364d88c8d8b6026bbc9ffa48c
2019-10-08T17:02:44.209+0800 I CONTROL  [initandlisten] allocator: system
2019-10-08T17:02:44.209+0800 I CONTROL  [initandlisten] modules: none
2019-10-08T17:02:44.209+0800 I CONTROL  [initandlisten] build environment:
2019-10-08T17:02:44.209+0800 I CONTROL  [initandlisten]     distarch: x86_64
2019-10-08T17:02:44.209+0800 I CONTROL  [initandlisten]     target_arch: x86_64
2019-10-08T17:02:44.209+0800 I CONTROL  [initandlisten] options: {}
2019-10-08T17:02:44.211+0800 I STORAGE  [initandlisten] exception in initAndListen: NonExistentPath: Data directory /data/db not found., terminating
2019-10-08T17:02:44.211+0800 I NETWORK  [initandlisten] shutdown: going to close listening sockets...
2019-10-08T17:02:44.211+0800 I NETWORK  [initandlisten] removing socket file: /tmp/mongodb-27017.sock
2019-10-08T17:02:44.211+0800 I CONTROL  [initandlisten] now exiting
2019-10-08T17:02:44.211+0800 I CONTROL  [initandlisten] shutting down with code:100
?  /Users/william > 

I tried to install MongoDB with brew:

brew install mongodb

?  /Users/william > brew install mongodb
Updating Homebrew...
Error: mongodb: unknown version :mountain_lion

Any help?

Answer 1

This is the main error:

exception in initAndListen: NonExistentPath: Data directory /data/db not found., terminating

Catalina has a surprise change: it won't allow changes to the root directory (this was discussed in a forum thread as well):

% sudo mkdir -p /data/db
mkdir: /data/db: Read-only file system

Unfortunately, this is not spelled out explicitly in Apple's Catalina release notes, other than a brief mention in Catalina features:

macOS Catalina runs in a dedicated, read-only system volume

Since the directory /data/db is coded as MongoDB default, a workaround is to specify a different dbpath that is not located on the root directory. For example:

mongod --dbpath ~/data/db

This will place MongoDB's data in your home directory. Just make sure that the path ~/data/db actually exists.

Alternative method

An alternative method is to follow the instructions at Install MongoDB Community Edition on macOS by leveraging brew:

brew tap mongodb/brew
brew install mongodb-community

This will create some additional files by default:

• the configuration file (/usr/local/etc/mongod.conf)
• the log directory path (/usr/local/var/log/mongodb)
• the data directory path (/usr/local/var/mongodb)

To run mongod you can either:

• Run the command manually from the command line (this can be aliased for convenience):

  mongod --config /usr/local/etc/mongod.conf
  

• Run MongoDB as a service using brew services. Note that this will run MongoDB as a standalone node (not a replica set), so features that depends on the oplog e.g. changestreams will not work unless you modify the mongod configuration file:

  brew services start mongodb-community