Upgrading older mongo database after unintentional mongo version upgrade

I solved the problem by installing the older version of mongodb on a system for which it wasn't a problem to get it pre-packaged (well, Windows 10, even though oficially it's stated the package is for Windows Server 2008), copying the database files (contents of /var/lib/mongodb) there, running it with --dbpath param (mongod --dbpath /path/to/dbfiles), setting the compatibility flag according to the docs and finally copying the db files back to the server.

Would like to know about a better option, but it's good to know the db files are easily transferable to another system, even another architecture (the db was relatively simple and small though).

Running mongod --repair worked for me.

here similar issue, unintentionally upgrade from 4.2.1 to 4.4.3, then mongodb can NOT started..

Final worked solution:

1. uninstall (latest, but not worked version: 4.4.3)

brew uninstall mongodb-community

2. reinstall, old but worked 4.2.1

brew install mongodb-community@4.2

3. run

• for now: brew services run mongodb-community@4.2
• for now and set bootable: brew services start mongodb-community@4.2

4. check status

brew services