Locking updates means that the balena supervisor will not be able to kill your application. This is meant to be used at critical sections of your code where you don't want to be interrupted, or to ensure that updates or environment variable changes take effect at certain times.
In order to do this, users can create a lockfile in a way that it has exclusive access, which will prevent the device supervisor from killing and restarting the app. As with any other lockfile, the supervisor itself will create such a file before killing the app, so you should only create it in exclusive mode. This means that the lockfile should only be created if it doesn't already exist. The exclusive access is achieved by opening the lockfile with the [O_EXCL and O_CREAT flags](https://linux.die.net/man/3/open), and several tools exist to simplify this process with examples given [below](#creating-the-lockfile).
For multicontainer applications, a release will only be updated if all of the services can be updated. While locks are per-service, having the update lock in a single service will prevent all services from updating to a new release.
The presence of a lockfile will ensure that your application does not get killed, but updates will still be downloaded by the supervisor, ready to be applied once the lockfile no longer exists.
On devices running supervisor 7.22.0 and higher, the lockfile is located at `/tmp/balena/updates.lock`. This lock is cleared automatically when the device reboots, so the user app must take it every time it starts up.
On older devices (with v4.0.0 <= supervisor version <v7.22.0)thelockislocatedat`/tmp/resin/resin-updates.lock`.Thelatestsupervisorversionsstilltakethelockatthislegacypathforbackwardscompatibility.
assumption that updates are locked (see [issue #20](https://github.com/balena-os/balena-supervisor/issues/20)). We therefore strongly recommend switching to the new lock location as soon as possible.
__Note:__ Just creating the lockfile, for example by using `touch /tmp/balena/updates.lock`, is not adequate to prevent updates. A file created in this way won't have the exclusive access flag set, and thus does not provide reliable locking.
One simple way to create a lockfile is using [lockfile](https://linux.die.net/man/1/lockfile) (available for example in Debian from the `procmail` package):
The easiest way to do this is to use the 'Override the update lock ...' toggle in the [Fleet or Device Configuration][device-configuration] page. Go to the configuration page of the device or fleet, locate the 'Override the update lock ...' item, click the activate button, and set the toggle to enabled. Disable the toggle afterwards in order to restore the update locks.
Also, you can programatically do this by hitting the `/v1/update` endpoint of the [supervisor HTTP API][supervisor-api], with `{ "force": true }` as body.