borg fills the disk, even though it shouldn't (causing no space left on device)

[mikae1]

The manual reads:

If you run a backup that stops due to a disk running full, Borg will roll back, delete the new new segment file and thus freeing disk space automatically.

That did not happen. When I ran a backup to an external disk it completely ran out of space and now I can not even run borg list or borg prune on it because borg tells me:
Failed to create/acquire the lock /run/media/username/external_disk/machine/lock.exclusive ([Errno 28] No space left on device: '/run/media/username/external_disk/machine/lock.exclusive.g2o0oj6d.tmp').

I have nothing else than this borg backup on the disk, so I can't free up space.

Expected outcome when space ran out would have been: borg acts as the manual says.

Now I probably have to get a larger disk to solve the problem.

[ThomasWaldmann]

Yeah, that might be not totally reliable. But note that it also says "Borg cannot work if you really have zero free space on the backup disk, ..." in the section you linked.

What you can do is delete the last segment file borg_repo_dir/data/N/M, with N being the highest numbered subdirectory there and M being the file(s) with the highest number(s).

That will remove data from your last backup(s), but the very last backup is incomplete anyway.

After that, it will have space again to create the lock.

Next step is running borg check --repair --progress -v ... to bring the repository into a known-good state.

Then you can use borg list / borg delete / borg prune AND borg compact to free more space.

And then take steps as documented that this never happens again by reserving some space on that disk or better monitoring disk space.

[ThomasWaldmann]

BTW, if you did not run borg as root (for the borg process that managed that repository) and you used ext2/3/4 for the filesystem and you used default parameters when creating that filesystem (5% space reserve), there might be some reserved space (only for root, not for normal users) on the filesystem.

ext2/3/4 - check reserved space:

tune2fs -l /dev/sdXN

ext2/3/4 - reduce reserved space:

tune2fs -m 1 /dev/sdXN  # reduce to 1% reserved space