filesystem has unsupported features - fix with debugfs

On occasion I need to build machines with old distributions - usually, this involves copying the disks using tar or rsync onto a server that has been booted off a live CD such as GRML. When making an ext3 filesystem via a newer distribution such as GRML for what will be an older system such as redhat 7.2, certain ext3 features are not supported by the kernel and/or libraries (not sure which), and so it will complain when starting up, though it will still boot. I am not sure if it affects stability of the system. You can however remove the newer features put by there by the new boot CD by using debugfs. debugfs will do this on mounted filesystems as well. As a basis for comparison, I look at what one of the older servers has as the supported features by running debugfs on filesystems there, and then remove the features on the newly-built machine. You may also be able to get supported features in other ways, perhaps via logs or debugfs or researching what features are supported in the particular kernel/libraries/user-space tools or whatever enables the feature. I took the lazy method that is available though!

There is context sensitive

debugfs comes with its own shell, a bit like grub. You can type 'help' to access list of supported commands/operations. For instance, type 'feature' to list supported fs features, and 'feature - etc..' to delete features. Alternatively, you can run commands via the '-R' option from standard bash or other shell, or you can create a file with the operations you want to perform and send them to debugfs.

Very cool :)