Git "filtering not recognized by server" - Partial Clone Fails

A partial clone with --filter=blob:none asks the server to omit object data and fetch it lazily. If the remote does not advertise the partial-clone capability, the filter is ignored or a later command fails fetching a blob on demand.

What this error means

A git clone --filter=blob:none warns that filtering is not recognized, or a later operation fails trying to lazily fetch a missing object. It happens against servers or mirrors that have partial clone disabled.

warning: filtering not recognized by server, ignoring
# or, on lazy fetch:
fatal: missing blob object 'a1b2c3...'
fatal: unable to read tree (a1b2c3...)

Common causes

The server does not support partial clone

Partial clone needs the filter capability on the remote. Older Git servers, some mirrors, and certain hosting tiers do not advertise it, so the --filter request is silently ignored.

Lazy fetch cannot reach the promisor remote

A partial clone defers downloading blobs until needed. If the runner later goes offline from the promisor remote, the on-demand fetch of a missing object fails.

How to fix it

Fall back to a shallow clone

When the server lacks partial-clone support, a shallow clone gives a similar size reduction without needing the filter capability.

git clone --depth 1 https://github.com/org/repo.git
# instead of: git clone --filter=blob:none ...

Materialize the objects you need

If you must use partial clone, backfill the blobs you will reference so no lazy fetch happens mid-job.

git clone --filter=blob:none https://github.com/org/repo.git
cd repo
git fetch origin --refetch   # or: git rev-list --all | git cat-file --batch-check

How to prevent it

• Verify the remote advertises the filter capability before using --filter.
• Prefer shallow clones for simple CI size reduction.
• Keep the promisor remote reachable for the whole job when using partial clone.

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