fsck [LWN.net]

fsck

Posted Mar 20, 2007 12:53 UTC (Tue) by etienne_lorrain@yahoo.fr (guest, #38022)
In reply to: fsck by nix
Parent article: The 2007 Linux Storage and File Systems Workshop

An image of the partition before applying the EXT3 journal would certainly be usefull, so quite a few full DVDs; but you always think: well, I've lost two or three files, just begin the recovery, will not be too bad... well it seems a bit more, give the "always answer yes" option to fsck... well it begin to feel bad... well there was nothing that important on the filesystem... and too late to do it right anyways.
That is at those times that you like the separate partition for valuable files, with simple partition schemes and no optimised filesystem (choice in between FAT and ext2fs).
The thing I should have done is to run an e3fsck after I had few crashs with the floppy driver on this PC (a bug already solved leaving interrupt disabled so power-off in X), but it was 6 to 10 sessions (i.e. few hours of work followed by shutdown/power off) before so it should have been handled by the EXT3 journal recovery.
I still should have forced the check from another distribution to be sure - or the FC6 live CD... too late.

Etienne.

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fsck

Posted Mar 20, 2007 14:55 UTC (Tue) by nix (subscriber, #2304) [Link]

If you give e2fsck the -y option, IMHO you deserve everything you get. There's a *reason* it's not the default. (And, yes, when I'm lucky enough to have enough accessible storage and a major filesystem does south without recent backups, I *do* gzip up the filesystem image and back it up before doing a fsck. Perhaps I could use e2image but I've never dared risk it.)

fsck

Posted Mar 20, 2007 16:02 UTC (Tue) by bronson (subscriber, #4806) [Link]

Unless you're an ext3 filesystem engineer, how are you supposed to know what fixes to make?? If fsck asks my mom, "1377 unreferenced nodes, delete? (Y)" (whatever a typical error looks like; it's been a while), what is she supposed to do?

The only two modes that the average Linux user can run fsck in:
- All Y, which you say is a bad idea.
- All N, in which case there's no point.

Maybe fsck could offer an "all trivial" setting, where it would automatically make fixes that it thinks are unlikely to cause data loss. If a bigger problem is found, fsck could bail out saying, "Serious errors found, back up partition before repairing!"

This is the same problem as Windows users splatting "Yes" every time their OS asks, "Do you want to allow a connection to sdlkh.phishing.org" except that the fsck questions are even less understandable!

fsck

Posted Mar 20, 2007 17:02 UTC (Tue) by nix (subscriber, #2304) [Link]

Your points have merit: it's hard to work out which changes are safe. That's why I tend to e2fsck first with -n, and review the list to see if there are a lot of changes or they look intuitively frightening. If they do, it's image-first time, so I can retry with more n answers if fsck goes wrong.

(The `all trivial' option already exists: it's what you get if you run e2fsck with -a. If e2fsck says you must run fsck manually, that means it has nontrivial fixes to make. In my experience this is rare indeed, even in the presence of repeated power failures or qemu kills while doing rm -r.)

This is yet one more place where a CoW device-mapper layer would be useful: instead of doing huge copies, you could just do the e2fsck in a CoWed temporary image (maybe mounted on a loopback filesystem somewhere :) ) and see if that worked...