mmk lock

Shows who holds the migration lock right now. It changes nothing.

npx mmk lock [--json]

When you need it

Every mmk up, down, redo, import and namespace adopt takes a lock first, so two runs can't overlap. When a run fails with LOCK_ALREADY_HELD, or before you start one, mmk lock tells you who has it: the host, the process and the user, since when, and when it frees itself.

It never takes, renews or releases the lock, and it connects without writing anything, so it's safe to run at any time, on any database, with a user that has only the read role.

What it looks like

$ npx mmk lock
Lock held by namespace "orders-worker": pid 48213 on deploy-runner-7 (ci) since 2026-06-05 12:01:33
If the holder crashed, the lock frees itself at 2026-06-05 12:03:03; `mmk unlock` releases it now (check the holder first)

If nobody holds it:

$ npx mmk lock
No migration lock is currently held

A run that was killed leaves its lock behind until the lock goes stale. Once it has, mmk says so, and you don't need mmk unlock: the next run takes it over.

$ npx mmk lock
Lock left by namespace "orders-worker": pid 48213 on deploy-runner-7 (ci) since 2026-06-05 12:01:33
It has gone stale (the holder stopped renewing it), so the next run takes it over

On a database that several repos share, the holder might be another repo. mmk says so, the way mmk unlock does.

Options

Option	What it does
--json	Print { "holder": …, "stale": … }.

The global flags work here too.

{
  "holder": {
    "lockedAt": "2026-06-05T12:02:03.000Z",
    "pid": 48213,
    "host": "deploy-runner-7",
    "executedBy": "ci",
    "namespace": "orders-worker",
    "acquiredAt": "2026-06-05T12:01:33.000Z",
    "expiresAt": "2026-06-05T12:03:03.000Z"
  },
  "stale": false
}

holder is null when no lock is held, and then stale is false. stale is judged on the database server's clock, by the same rule a run uses to take a lock over. lockedAt moves forward each time the holder renews the lock; acquiredAt is when it first took it. namespace, acquiredAt and expiresAt are there for holders running mongo-migrate-kit 1.5 or newer.

From code

const { holder, stale } = await migrator.lockStatus(); // LockStatus, changes nothing