mjhjmtu

The OS is Ubuntu 17.10 and I've been trying to recover(undelete) with extundelete.
(The File System is ext4.)

This didn't work. So, I tried with

extundelete /dev/mapper/ubuntu--vg-root --restore-file /home/chan/origol/routes/user.js

And It worked.

However, I got another problem.

Loading filesystem metadata ... extundelete: Block bitmap checksum does not match bitmap when trying to examine filesystem

I couldn't find any information about it. How can I solve this problem?

You probably have the metadata_csum feature enabled in your filesystem, but extundelete does not understand this feature and is not updating the block bitmap checksum when it is modifying it to indicate the blocks from the undeleted file are again in use. That said, extundelete shouldn't be modifying a filesystem that has features it does not understand, since this can lead to more significant filesystem corruption.

You should be able to fix this by running e2fsck -fy on the filesystem. It would probably also be worthwhile to submit a bug report (ideally with an accompanying patch) to the extundelete author/maintainer to both fix it to compute the metadata checksums, as well as ensure that it does not try to open filesystems for which it does not understand INCOMPAT features, and only allow read-only opens for filesystems with RO_COMPAT features.