Learn the DD command

psjoberg · 09-19-2006, 02:00 PM

I'm trying to use dd to copy whatever data I can from a bad to a good disk but bumped into a problem that dd retires the same sector forever (or at least hours).

For example, I did

Code:

strace dd if=/dev/sdb of=/dev/sdc bs=512 seek=122030010 skip=122030010 count=1 conv=noerror,notrunc

and exepected it to fail to copy one sector (that one isn'r readable) but it did retry over and over. The stray shows how it does

Code:

lseek(0, 0, SEEK_CUR)                   = 62479380480
ioctl(0, MGSL_IOCSTXIDLE or MTIOCGET or SNDCTL_MIDI_MPUCMD, 0x7fffcc749dc0) = -1 ENOTTY (Inappropriate ioctl for device)
lseek(0, 512, SEEK_CUR)                 = 62479380992
read(0, 0x50c000, 512)                  = -1 EIO (Input/output error)

repeated over and over for 1h.
Is it a bug in dd (v5.93) or did I fiddle wrong with my parameters ?

/ps

jiml8 · 09-20-2006, 07:44 AM

Try moving the conv= to the front of the dd statement.

booyaadewd · 09-20-2006, 01:10 PM

Good Morning,

I have a question. I would like to use dd to wipe a drive, i can do this no problem with the command:

dd if=/dev/zero of=/dev/hda bs=1024

what i want to do is actually email a log with the date, time, computer name, and wether the script completed okay to someone.

How could i do this at the command line? Keep in mind i would like to use the a very minimal kernel install to do this. (I think im going to have to add mail to tthe kernel)

thanks
booyaa

NapalmD · 09-20-2006, 01:25 PM

Quote:

Originally Posted by NapalmD

lol, it is working fine, despite that 15GB problem!
I have a temporary HD(80Gb) to put the 40GB data to fix this problem... sorry but I didnt understand correctly your last tips...
so 1st I need to put hda1 (15gb) in hdb1 in some way, but I need to create partitions 1st in this temporary HD right?
then will I need to format the hda1? how is that done?

then, transfer the data back to where it belongs but using all space provided by 37gb partition, how is that dd done?

I have read the 1st post, but it seems that it didnt work the way I liked. sorry but because I'm not good in english maybe I missed some word

thanks

I was able to do the trick with cp -a * /mnt/backup
then mkfs.ext3 /dev/hda1
then files back with cp -a again..
then it certainly would work...
I've read this in a google search, it seems that dd does not work right when copying from a small to a bigger drive...

linuxquestionsorg42 · 09-20-2006, 04:58 PM

Quote:

Originally Posted by AwesomeMachine

dd [I][COLOR="DarkSlateGray"][SIZE="4"]Most comprehensive documentation and example sheet for one of the most useful linux/UNIX commands, "dd".

Will this be in the Linux Tutorial section?

Thank you.

Emmanuel_uk · 09-21-2006, 01:34 AM

AwesomeMachine,

You have done a great

work/tutorial

. If this goes to the TLDP
or if you keep enhancing the thread, here are some suggestions:

add http://dcfldd.sourceforge.net/ where ddrescue is
maybe talk about http://linux.maruhn.com/sec/sdd.html
(I have no experience with sdd)

external links (this one was quite comprehensive
"Unix dd command and image creation"
by Softpanorama: (slightly skeptical) Open Source Software Educational Society
http://www.softpanorama.org/Tools/dd.shtml

I let you know if I have further ideas

AwesomeMachine · 09-26-2006, 03:17 AM

Quote:

Originally Posted by booyaadewd

Good Morning,

I have a question. I would like to use dd to wipe a drive, i can do this no problem with the command:

dd if=/dev/zero of=/dev/hda bs=1024

what i want to do is actually email a log with the date, time, computer name, and wether the script completed okay to someone.

How could i do this at the command line? Keep in mind i would like to use the a very minimal kernel install to do this. (I think im going to have to add mail to tthe kernel)

thanks
booyaa

If you boot from a live CD, such as Helix, which is linked in the OP, you can run dd, and email the logs entries with the live CD. Knoppix would also work for this. I don't recommend using the same kernel you are erasing to run dd. You should use a live CD.

AwesomeMachine · 09-26-2006, 03:18 AM

Quote:

Originally Posted by linuxquestionsorg42

Will this be in the Linux Tutorial section?

Thank you.

In the dd tutorial there is a link to this post.

AwesomeMachine · 09-26-2006, 03:20 AM

Quote:

Originally Posted by psjoberg

I'm trying to use dd to copy whatever data I can from a bad to a good disk but bumped into a problem that dd retires the same sector forever (or at least hours).

For example, I did

Code:

strace dd if=/dev/sdb of=/dev/sdc bs=512 seek=122030010 skip=122030010 count=1 conv=noerror,notrunc

and exepected it to fail to copy one sector (that one isn'r readable) but it did retry over and over. The stray shows how it does

Code:

lseek(0, 0, SEEK_CUR)                   = 62479380480
ioctl(0, MGSL_IOCSTXIDLE or MTIOCGET or SNDCTL_MIDI_MPUCMD, 0x7fffcc749dc0) = -1 ENOTTY (Inappropriate ioctl for device)
lseek(0, 512, SEEK_CUR)                 = 62479380992
read(0, 0x50c000, 512)                  = -1 EIO (Input/output error)

repeated over and over for 1h.
Is it a bug in dd (v5.93) or did I fiddle wrong with my parameters ?

/ps

Try using ddrescue. It is linked in the OP. It works the same way as dd, but it will work with bad media.

AwesomeMachine · 09-26-2006, 03:23 AM

Quote:

Originally Posted by NapalmD

lol, it is working fine, despite that 15GB problem!
I have a temporary HD(80Gb) to put the 40GB data to fix this problem... sorry but I didnt understand correctly your last tips...
so 1st I need to put hda1 (15gb) in hdb1 in some way, but I need to create partitions 1st in this temporary HD right?
then will I need to format the hda1? how is that done?

then, transfer the data back to where it belongs but using all space provided by 37gb partition, how is that dd done?

I have read the 1st post, but it seems that it didnt work the way I liked. sorry but because I'm not good in english maybe I missed some word

thanks

Use the command mke2fs to make a ext2 or ext3 file system. man mke2fs for info

Tinkster · 09-26-2006, 03:29 AM

Have you considered overhauling the original post in terms of layout/paragraph
and colorisation? The content is fine, but it's such an eye-sore.

Cheers,
Tink

AwesomeMachine · 09-26-2006, 03:53 AM

Quote:

Originally Posted by Tinkster

Have you considered overhauling the original post in terms of layout/paragraph
and colorisation? The content is fine, but it's such an eye-sore.

Cheers,
Tink

Tink,

I'm almost at the maximum word count in the OP. I don't have much flexibility on paragraph styling, although I admit a little more "white space" would be attractive. Blank lines count toward total word count, so I'm in a pinch. If you would PM me I would be willing to listen to some thoughts on colorisation. I myself am not able to PM you for lack of sufficient board privileges. I'm open to suggestions, but this is off topic.

sardaukar_siet · 09-26-2006, 04:53 AM

Hello.

I used to extract boot info from Linux partitions by copying the first 512 bytes to a file, like so :

dd if=/dev/<partition with boot info> of=bootsect.lnx bs=512 count=1

The produced file is suitable to work with XP's ntldr, editing boot.ini. This way dual boot is clean and easy, since upgrading Windows won't wipe Linux's boot info as long as you keep the file.

But this only works for simple partitions. How can I make it work with LVM or MDraid partitions? Where is the boot info located in them?

Thanks in advance!

AwesomeMachine · 09-27-2006, 02:59 AM

Quote:

Originally Posted by sardaukar_siet

Hello.

I used to extract boot info from Linux partitions by copying the first 512 bytes to a file, like so :

dd if=/dev/<partition with boot info> of=bootsect.lnx bs=512 count=1

The produced file is suitable to work with XP's ntldr, editing boot.ini. This way dual boot is clean and easy, since upgrading Windows won't wipe Linux's boot info as long as you keep the file.

But this only works for simple partitions. How can I make it work with LVM or MDraid partitions? Where is the boot info located in them?

Thanks in advance!

Your are speaking of sector 1 on the HDD. This holds the partition table, among other things. Raid and LVM are special considerations. With software raid you must disconnect all but one disk, copy the info you need, make all your changes, and rebuild the raid array. This only works with RAID 0. Other types of raid will not respond well to dd. LVM is a special type of volume where the description is kept in an extended partition. How to find this information is really quite complex, and you have to have a good eye for what you looking for. These two types of applications are poor for using dd.

prashant.gupta · 09-27-2006, 04:24 AM

This article on dd command is very nice. Can we get the dd command for windows/dos?