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The following page summarizes various considerations for downgrading to 4.2. For specific instructions for your deployment type, see:
Before you upgrade or downgrade a replica set, ensure all replica set members are running. If you do not, the upgrade or downgrade will not complete until all members are started.
If you need to downgrade from 4.4, downgrade to the latest patch release of 4.2.
MongoDB only supports single-version downgrades. You cannot downgrade to a release that is multiple versions behind your current release. You may downgrade a 4.4-series to a 4.2-series deployment, however, further downgrading that 4.2-series deployment to a 4.0-series deployment is not supported.
If you need to downgrade from version 4.4, downgrade to 4.2.6 or a later version. You cannot downgrade to 4.2.5 or an earlier version.
Optional but Recommended. Create a backup of your database.
Before downgrading the binaries, you must downgrade the
featureCompatibilityVersion (fCV) to
Before downgrading the binaries, remove all persisted 4.4 features that are incompatible with 4.2.