How can fsck be so fast?

Question

Is it normal, that fsck on an SSD takes a second or two? I am on Linux Mint 17.3 and I called

sudo touch /forcefsck

EDIT: ext4 filesystem

What filesystem are you using? It's possible that a journaling filesystem will immediately go "oh, the journal looks ok, I didn't lose any transactions, all is well" — Ulrich Schwarz, Apr 07 '16 at 15:19
Did you reboot after running that `touch`? You're aware that forces an fsck on the next boot, correct? — derobert, Apr 07 '16 at 16:11
@don_crissti if you're familiar with fsck times on SSDs, please post an answer—do not use comments to answer the question. — derobert, Apr 07 '16 at 20:09
@derobert - I've been experiencing about the same times when forcing a `fsck` on an otherwise consistent `ext4`: less than 2 seconds. Not sure how to put that in an answer (sounds OK as a comment imo but really dumb as an answer so I'll leave it as a comment). — don_crissti, Apr 07 '16 at 21:45

score 0 · Answer 1 · answered Apr 07 '16 at 15:39

0

There are two kinds of fsck, "normal"

sudo fsck /dev/sdx

and "full"

sudo fsck -f /dev/sdx

Your computer runs a normal fsck at every boot, which is really fast. fsck -f obviously takes longer, but in newer filesystems (ext4) it's still quite fast. With SSD might as well double that, and your fsck -f shouldn't take long at all.

Warning: Never run those codes on a mounted disk. It can cause severe filesystem corruption.

answered Apr 07 '16 at 15:39

nebulon

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6

1

Not really, ext4 only has one type of fsck. It just tracks internally if it is needed—without `-f`, it only does an fsck if it thinks one is needed. With `-f`, it does one regardless. Refer to `man e2fsck`. – derobert Apr 07 '16 at 16:10
I've found fsck -f -t takes longer than fsck -t consistently, but I guess that's just anecdotal – nebulon Apr 07 '16 at 19:55
that's probably because without -f it didn't actually run an fsck. Not entirely sure of the behavior of -t as I've never run fsck time trials... You can use tune2fs to set the fsck needed flag, BTW. – derobert Apr 07 '16 at 19:58
freaking ubuntu forums misled me. http://ubuntuforums.org/showthread.php?t=1680978 I wanted to edit the "f-ck" to fsck but apparently my time for that ran out. well I suppose that's good for everyone since that joke is old and tired. – nebulon Apr 07 '16 at 20:06
I can't believe 2 things: a) on kubuntu 16, `man fsck` DOES NOT have the `-f` option. Is it a hidden one??, WTF, how idiotic. Assume you have a half trusted device and you want to check it when you want, why can't linux allow you to do it. 2) Why this GREAT answer had -2 points is beyond me! – Angelos Pikoulas Oct 12 '18 at 22:47

score 0 · Accepted Answer · answered Apr 07 '18 at 09:03

Actual answer is, that the command on Linux Mint does not work as proven in this answer, section:

These two options did NOT work: Adding the /forcefsck empty file with

Please refer to the mentioned answer for more information, for instance as to how to actually force a file system check.

How can fsck be so fast?

2 Answers2