{"id":58,"date":"2017-10-30T00:13:43","date_gmt":"2017-10-30T00:13:43","guid":{"rendered":"http:\/\/tajdini.net\/blog\/?p=58"},"modified":"2020-12-20T11:17:55","modified_gmt":"2020-12-20T09:17:55","slug":"howto-repair-a-broken-ext4-superblock-in-ubuntu","status":"publish","type":"post","link":"https:\/\/tajdini.net\/blog\/cloud-and-devsecops\/howto-repair-a-broken-ext4-superblock-in-ubuntu\/","title":{"rendered":"HOWTO: Repair a broken Ext4 Superblock in Ubuntu"},"content":{"rendered":"

This has happened to me a few times, and it\u2019s not a nice problem to find yourself in. You computer won\u2019t boot, all your filesystem checks tell you you\u2019ve a bad superblock, but you cant seem to find how to fix it. Well, here goes \ud83d\ude42<\/p>\n

This guide is for ext4 , though I\u2019ll explain how other filesystems can be cured along the way. The easiest way to carry all this out, seeing as your computer probably won\u2019t boot at this stage, is to download and burn a copy of Parted Magic. Boot from that, and you\u2019ll access to a number of useful tools.<\/p>\n

First, figure out what partition we\u2019re dealing with.<\/p>\n

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1<\/div>\n<\/td>\n
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sudo<\/code> fdisk<\/code> -l<\/code><\/div>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n<\/blockquote>\n

The above will list all the partitions on all the drives in your computer. To recover a lost partition, your going to need Testdisk. Testdisk is included in Parted Magic, and there\u2019s a great guide on their site. For this though, we just need the partition number, such as \/dev\/sda3 or \/dev\/hdb1.<\/p>\n

Now, make sure your superblock is the problem, by starting a filesystem check, replacing xxx with your partition name. Here, you can change ext4 to ext3, or ext2 to suit the filesystem.<\/p>\n

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1<\/div>\n<\/td>\n
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sudo<\/code> fsck<\/code>.ext4 -<\/code>v<\/code> \/dev\/xxx<\/code><\/div>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n<\/blockquote>\n

If your superblock is corrupt, the output will look like this<\/p>\n

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1<\/div>\n
2<\/div>\n
3<\/div>\n
4<\/div>\n
5<\/div>\n
6<\/div>\n
7<\/div>\n
8<\/div>\n
9<\/div>\n
10<\/div>\n
11<\/div>\n<\/td>\n
\n
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fsck<\/code> \/dev\/sda5<\/code><\/div>\n
fsck<\/code> 1.41.4 (27-Jan-2009)<\/code><\/div>\n
e2fsck 1.41.4 (27-Jan-2009)<\/code><\/div>\n
fsck<\/code>.ext4: Group descriptors <\/code>look<\/code> bad... trying backup blocks...<\/code><\/div>\n
fsck<\/code>.ext4: Bad magic number <\/code>in<\/code> super-block <\/code>while<\/code> trying to <\/code>open<\/code> \/dev\/sda5<\/code><\/div>\n
<\/div>\n
The superblock could not be <\/code>read<\/code> or does not describe a correct ext4<\/code><\/div>\n
filesystem.\u00a0 If the device is valid and it really contains an ext4<\/code><\/div>\n
filesystem (and not swap or ufs or something <\/code>else<\/code>), <\/code>then<\/code> the superblock<\/code><\/div>\n
is corrupt, and you might try running e2fsck with an alternate superblock:<\/code><\/div>\n
e2fsck -b 8193 &lt;device&gt;<\/code><\/div>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n<\/blockquote>\n

Now lets find where your superblock backups are kept.<\/p>\n

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1<\/div>\n<\/td>\n
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sudo<\/code> mke2fs -n <\/code>\/dev\/xxx<\/code><\/div>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n<\/blockquote>\n

Down at the bottom of this output, should be a list of the backups<\/p>\n

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1<\/div>\n
2<\/div>\n<\/td>\n
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Superblock backups stored on blocks:<\/code><\/div>\n
32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208<\/code><\/div>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n<\/blockquote>\n

Your almost there. Finally, restore the superblock from the backup, again replacing the x\u2019s with your partition name, and block_number with the first backup superblock.<\/p>\n

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1<\/div>\n<\/td>\n
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sudo<\/code> e2fsck -b block_number <\/code>\/dev\/xxx<\/code><\/div>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n<\/blockquote>\n

Now reboot, and your superblock should be fixed. If it\u2019s not, repeat the steps, but restore a different backup superblock \ud83d\ude42<\/p>\n","protected":false},"excerpt":{"rendered":"

This has happened to me a few times, and it\u2019s not a nice problem to find yourself in. You computer won\u2019t boot, all your filesystem checks […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[222,227],"tags":[239,241,4,5,6],"class_list":["post-58","post","type-post","status-publish","format-standard","hentry","category-cloud-and-devsecops","category-linux-and-open-source","tag-backup-and-recovery","tag-cloud-security","tag-linux","tag-ubuntu"],"_links":{"self":[{"href":"https:\/\/tajdini.net\/blog\/wp-json\/wp\/v2\/posts\/58","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/tajdini.net\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/tajdini.net\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/tajdini.net\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/tajdini.net\/blog\/wp-json\/wp\/v2\/comments?post=58"}],"version-history":[{"count":2,"href":"https:\/\/tajdini.net\/blog\/wp-json\/wp\/v2\/posts\/58\/revisions"}],"predecessor-version":[{"id":60,"href":"https:\/\/tajdini.net\/blog\/wp-json\/wp\/v2\/posts\/58\/revisions\/60"}],"wp:attachment":[{"href":"https:\/\/tajdini.net\/blog\/wp-json\/wp\/v2\/media?parent=58"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/tajdini.net\/blog\/wp-json\/wp\/v2\/categories?post=58"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/tajdini.net\/blog\/wp-json\/wp\/v2\/tags?post=58"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}