User:Skierpage/Recovery: Difference between revisions

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Moved to http://userbase.kde.org/User:Skierpage/Disk_recovery
== Disaster! ==
I followed instructions to create a bootable SD card,
zcat blah.bootable.gz > /dev/sd''X''

This is dangerous because it overwrites the partition, but I had done it before, I knew there was nothing on my SD card and /dev/sda is my SD card.

But /dev/sda is my hard drive. The whole thing.

I checked with df and the size looked wrong, then I read my notes (should have done that first) and I was overwriting the wrong disk. Ctrl-C!

Then I tested the .gz file and it was corrupt, so I thought nothing had been written. My computer worked fine.

The next day I got an error coming out of standby about not reading C:\$MFT or something. So I decided to reboot. '''Big mistake''', I should have read partition tables, backed up some key files, and prepared for disaster.
: '''Rule 1''': do what you can while it's working.

Errors shutting down, then could not reboot, bad disk.

== Failed recovery ==
I couldn't find my Windows XP CD-ROM, even though Falcon Northwest make a big deal. Of course my Windows XP is so dramatically different thanks to all the updates and service packs that the original disk has been useless for System File Checking and file recovery and such. I had always meant to follow instructions to ''slipstream'' a new boot CD-ROM, where you make a fresh Windows CD-ROM that contains the latest files, but never did.
: '''Rule 2''' You need a boot disk around.

Falcon Northwest provided me a personalized Recovery Disk, I inserted this and nothing happened. Zero feedback.

== Into Kubuntu Live CD ==
I had built a Kubuntu Live CD. That booted fine.

The Kubuntu Live CD startup menu has "check disk" menu choice is useless, it just checks the CD-ROM. ''BUG:'' it is badly named.

So I ran the Live CD environment, and that worked fine.
I'm updating this web page from the Live CD. Hooray for free software that is happy for the world to make bootable CDs.

== Create a recovery disk/USB? ==

There are lots of dedicated "recovery CD" distributions. [http://distrowatch.com:80/search.php?category=Rescue&status=Active Distrowatch lists dozens], and the search leaves out the GParted distribution.

The problem is, I'm running from my only CD drive, so I can't burn another CD. Besides, I don't want to. I have gigabytes of space on my USB flash drive and SD memory card.

'''BUG:''' All the distributions I checked have '''crap''' guides to creating a bootable USB. Some even talk about making a floppy. The functionality and documentation for making a bootable USB needs to be separated from all these distributions.

== Use what I have ==
But I'm already running Linux. Kubuntu has the <tt>parted</tt> partition editor and the NTFS tools.

'''BUG:''' all the online web recovery instructions are crap. They tell you how to make a recovery CD or floppy or whatever, tell you to stick it in the machine and reboot, but fail to tell you what to do next. I guess they assume you'll walk through their beautiful menu system. ''It is stupid and short-sighted not to mirror help and guidelines on a web site.'' You should never have to create physical media and boot from it just to read documentation.

The first four pages of Google results for "linux partition recovery tutorial" are either sites trying to sell me something or yet another guide to creating a recovery CD. I gave up finding any explanation of what to do.

=== Find your hard drive ===
You have to find the UNIX device name for your disk, like hdb ("hard disk B") or sda ("SCSCI disk A" but also "Secure Digital" memory card). Then tools can access your disk using its entry in the special <tt>/dev</tt> directory. That's how I was able to scribble all over my hard drive in the first place.

Unfortunately, the /dev directory has lots of devices in it.

Another approach is to look for boot messages where the Linux kernel finds hardware devices. In a Linux console, enter
dmesg | grep disk
dmesg | grep drive

one of those should identify promising disk devices, or enter
dmesg | less
to read the whole boot thing (which might have hints about the state of the drive).

The best approach I've found is the somewhat undocumented one of looking in the special file <tt>/proc/partitions</tt>:
cat /proc/partitions

This identifies the partitions on the various devices, and their blocks. I guess if your hard drive was really badly trashed, it wouldn't have any partitions.

All these confirmed my hunch that /dev/sda is my poor hard drive. The good news is /proc/partitions showed my sda1 and sda2

=== Run parted ===
Now start <tt>parted</tt>. I should probably start this as the root user, using sudo
$ '''parted'''
Using /dev/sdb

that's wrong, I need to select /dev/sda.
(parted) '''help'''
... '' lots of commands''
(parted) '''select /dev/sda'''
Error: Error opening /dev/sda: Permission denied

so I do have to be root.
$ '''parted'''
GNU Parted 1.8.8
Using /dev/sda ''(good, now I'm root it picks sda as I can write to it)''
Welcome to GNU Parted! Type 'help' to view a list of commands.
&nbsp;
(parted) '''check'''
Partition number? '''1'''
Error: \8. is 512k, but it has 15994 clusters (63976k).
Ignore/Cancel? i
Fatal: Bad FAT: cluster 12 is cross-linked for \0.8. You should run dosfsck or scandisk.
there you go!
Let's see if the Linux partition is OK at least.
(parted) '''check'''
Partition number? '''1'''
Error: Partition doesn't exist.
Damn.
(parted) '''print'''
Model: ATA ST3120026AS (scsi)
Disk /dev/sda: 120GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos
&nbsp;
Number Start End Size Type File system Flags
1 17.4kB 2031MB 2031MB primary fat32 boot, lba

damn. That's completely wrong, I should have an enormous Windows partition. My original destructive ''zcat bootable'' scribbled a new partition table on the front of my disk that's completely wrong.

=== How bad is it ===

So as a result of scribbling over the front of the disk I have
# probably trashed the special loader (called grub? maybe) that let me boot from Windows or Linux
# probably trashed the Windows boot code, I'm not sure if it's in the first partition or somewhere else (the ''MBR'' "Master Boot Record" ?)
# probably trashed a big chunk of my NTFS Windows partition
# somehow completely messed up my Linux setup. With firefishe's advice I had set up the second half of the disk with root, swap, and home, now it's nowhere to be seen :-(

parted has a '''rescue''' command that will try to locate and revive partitions, but I thought there's a backup somewhere on the disk with partition information. The "MBR" again?? But since the first partition table looks OK, the program trusts it.

=== Recovering partitions ===
So now I'm back to trying to find out more about disk repair.
* http://sysblogd.wordpress.com/2008/01/05/data-recovery-with-linux-from-hard-drives-cd-roms-or-dvds/ seems useful, has other links.

Fortunately I [http://userbase.kde.org/User:Skierpage made notes] when I created the partition setup.

/dev/sda1 ntfs Size 90025 MB (83.8 GB) hopefully untouched
/dev/sda2 ext3 Mount / Format? checked Size 20003 MB Used 495 MB
/dev/sda3 ext4 Mount /home Format? checked Size 8003 MB Used unknown
/dev/sda4 swap Mount [blank] Format? [blank] Size 1998 MB Used unknown


Rather than guess at partitions with parted's rescue, [http://www.cgsecurity.org/wiki/TestDisk testdisk] sounded promising. But it's not on the Kubuntu live CD.

I tried using <tt>aptitude</tt> to install it, but that didn't work on the LiveCD. So I downloaded it. There's a [http://packages.ubuntulinux.org/testdisk Ubuntu package] available, navigate to the Jaunty version, get the URL of the amd64-bit version.
I have no idea how you can install new software to a read-only CD-ROM, so I did this in the temporary directory
cd /tmp
wget http://ubuntu.cs.utah.edu/ubuntu/pool/universe/t/testdisk/testdisk_6.10-1_amd64.deb

then
sudo dpkg -i testdisk_6.10-1_amd64.deb
to install.

=== testdisk to the rescue! ===
Praise be, this has a [http://www.cgsecurity.org/wiki/TestDisk_Step_By_Step pretty good intro], so I walked through that while running
sudo testdisk

and then turned on its expert mode and went slowly.

Like every other tool testdisk initially found only the bad small partition:
Disk /dev/sda - 120 GB / 111 GiB - CHS 14593 255 63
Current partition structure:
Partition Start End Size in sectors
&nbsp;
Warning: Incorrect number of heads/cylinder 63 (FAT) != 255 (HD)
Warning: Incorrect number of sectors per track 62 (FAT) != 63 (HD)
1 * FAT32 LBA 0 0 35 246 237 22 3966909 [LIVE]

But then its quick analyze command found my various Linux partitions!

And then, I pressed Enter then chose [Deep analyze], which went back through my disk slowly. Glory be, this found evidence of the bigger partition!

Disk /dev/sda - 120 GB / 111 GiB - CHS 14593 255 63
Partition Start End Size in sectors
D FAT32 0 0 35 246 254 63 3968021 [LIVE]
<span style="color:green">P HPFS - NTFS 0 1 1 10944 254 63 175831362 [Windows XP]</span>
D Linux 1902 0 1 4419 254 63 40451670
<span style="color:green">* Linux 10945 0 1 13376 254 63 39070080
D Linux 12139 2 1 14571 254 63 39086019</span
<span style="color:green">P Linux 13377 0 1 14349 254 63 15631245</span>
<span style="color:green">P Linux Swap 14350 0 1 14592 254 63 3903795</span>

wahoo! There's my Windows XP partition! It also found two extra bogus partitions, but by matching the size ("sector" is 1/2 kB) and using the info testdisk prints as you choose each partition, I figured out the proper partitions whose Start follows the End of the previous, and used the left and right arrow keys to enable the good partitions as shown, and delete the bad ones.

Press Enter, confirm writing the new thing. I'm not sure about the geometry errors.

Then it immediately displayed information about my NTFS partition:
Boot sector
Status: Bad
&nbsp;
Backup boot sector
Status: OK
&nbsp;
Sectors are not identical.
&nbsp;
A valid NTFS Boot sector must be present in order to access
any data; even if the partition is not bootable.

so I chose its [Backup BS] to copy the backup boot sector.

I tried [Repair MFT] to check the NTFS Master File Table, but that requires rebooting

=== Testdisk glitches ===

==== Quit for previous menu is odd ====
[Quit] everywhere to return to previous menu is very confusing. It should support [Esc]ape key, and the command should be [Back]

==== Analyze forces a Quick search ====
Also, if you choose analyze, you have a [Quick search] option, so there's no way to return to the main menu. You have to start a quick search. If you stop that, it'll be half-way through finding the partitions, so it looks as if it's lost all the information I've carefully brought back.

It's crazy that the only way I can see the current MBR is by choosing "Advanced".

So the main menu should have a "Current status" that shows
# what's on the disk MBR and partition info
# indicator if what testdisk has in memory is different (because you haven't written it yet)
# if not, show what's in its idea of the MBR and partitions is
# any other info it has or hasn't written to disk.

==== Ctrl-C ====
I tried to copy some text to here with Shift+Ctrl+C, and accidentally pressed Ctrl+C and testdisk immediately exited. Please trap Ctrl+C and ask "Are you sure?"

==== give user-friendly MB/KB size ====
When people are looking for partitions, they probably know the size in kB or kibibytes, but not in sectors. So maybe in parentheses give a user-friendly size like 5,203 KB or 12,304 MB.

==== Add partition is confusing ====
This is weird. First, I thought this would add the partition that testdisk had found that I've highlighted with the cursor keys, since D(eleted) is the opposite of Add.

Then, when I really did want to add a partition, the information line has no explanation
D No partition 0 0 1 1020 251 62 15952104

and I can't choose a particular partition type with the cursor, it highlights a row of three at a time!!

Latest revision as of 01:47, 4 June 2009

Moved to http://userbase.kde.org/User:Skierpage/Disk_recovery

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