Dir-overlay-install

General Discussions
1

Hello Mender,

I am trying https://github.com/mirzak/dir-overlay-install with read-only filesystem.

Should we modify dir-overlay-install scripts to enable update on read-only filesystem?
What would be correct way to handle update on read-only filesystem?

Some logs:
Oct 13 21:16:39 iqube mender[2137]: time=“2020-10-13T21:16:39Z” level=info msg="Update module output: tar: can’t remove old file ./usr/bin/app: Read-only file system"
Oct 13 21:16:39 iqube mender[2137]: time=“2020-10-13T21:16:39Z” level=error msg=“Update module terminated abnormally: exit status 1”
Oct 13 21:16:39 iqube mender[2137]: time=“2020-10-13T21:16:39Z” level=error msg=“Update module terminated abnormally: exit status 1”
Oct 13 21:16:39 iqube mender[2137]: time=“2020-10-13T21:16:39Z” level=error msg=“transient error: Update module terminated abnormally: exit status 1”
Oct 13 21:16:39 iqube mender[2137]: time=“2020-10-13T21:16:39Z” level=error msg=“transient error: Update module terminated abnormally: exit status 1”
Oct 13 21:16:39 iqube mender[2137]: time=“2020-10-13T21:16:39Z” level=info msg=“State transition: update-install [ArtifactInstall] -> rollback [ArtifactRollback]”

Many thanks.
Rostislav

1 Like
2

What would your objective be in doing this type of update to a read only filesystem? Usually that is enabled to ensure that the entire filesystem is identical to what was originally installed so doing incremental updates is a bit odd here.

You can temporarily enable read-write in a pre-install state script:

$ sudo mount -o remount,rw /

and then put it back in read-only mode after the install:

$ sudo mount -o remount,ro /

But note that if you are using RO for purposes of mender-binary-delta updates, this will not work. Applying the binary deltas requires that the active filesystem be completely unmodified.

Drew

3

Drew,
we use RO to ensure that filesystem on SD card will not be broken e.g. when there is power failure. Many thanks for the tips.
Rostislav