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Sending a USR1 signal to a running ‘dd’ process makes it print I/O
statistics to standard error and then resume copying.
$ dd if=/dev/zero of=/dev/null& pid=$!
$ kill -USR1 $pid
I still haven't found how to dd a partition out of a sparse file
Sending a USR1 signal to a running ‘dd’ process makes it print I/O
statistics to standard error and then resume copying.
$ dd if=/dev/zero of=/dev/null& pid=$!
$ kill -USR1 $pid
I still haven't found how to dd a partition out of a sparse file
For everyone who doesn't know, a sparse file is a placeholder of a certain size on a hard drive. It doesn't take up as much disk space as its size. It just reserves space for a large file. One must populate the sparse file with something, like zeroes for instance. I have tried dd with everything to do with sparse files and find it works fine. I don't know how or why one would need to dd a partition out of a sparse file. If the sparse file has a file system on it it could be mounted as a loop back device partition, but to use dd on such a thing you wouldn't need to mount it, but only:
dd if=/home/sam/sparsefile.img of=/dev/sda3
Sparse files withing a partition also dd to the new partition perfectly.
A useful example of a sparse file is this:
dd if=/dev/zero of=/dev/ram7 bs=4096 count=4096
to make a ramdisk into a ramdrive. If you put a file system on this device you can mount it just like a HDD, and write files to it. In the OP there is an example of this, with the proper command line to format and mount the drive. A ramdrive has throughput comparable to HDD cache speeds (950 MB/s Ramdrive vs 50 MB/s Sequential disk reads vs 950 MB/s HDD cache transfers) If you are using
a web browser it can be helpful to place the browser caches in a ramdrive so it doesn't need to search 400,000 cached jpg files off the disk platters every time you go to a new web site. The ramdrive is also useful for working on large documents, or programming projects which require many compiles.
One thing you've impressed upon me is how dangerous this command can be if misused. So I'd like to verify that I understand you correctly before I attempt to use the snippet of code that I've gotten from you.
One thing you've impressed upon me is how dangerous this command can be if misused. So I'd like to verify that I understand you correctly before I attempt to use the snippet of code that I've gotten from you.
Files need to be placed in a directory, within a file system. Files cannot be directly written to devices. The way to write to a file is to specify a path, starting with the mount point of the drive. For the / directory, which is mounted as root you begin with /. I always use /home/sam in my examples.
Quote:
Originally Posted by CyberCod
This (from what I gather) will back up the MBR of hda to a file called MBR.image, in the /hda3/backup directory... yes?
Quote:
Originally Posted by CyberCod
and to restore the mbr would be the opposite...
which would be
My other question is, would this also back up the grub portion of the MBR? would restoring this restore grub (assuming it is installed) as well?
You can always reinstall grub from an install CD/DVD, which would be the easy, correct method, I have found, when cloning to different sized partitions, especially if there are multiple os's involved, and then you might still need to edit /boot/grub/menu.lst. I strongly do not suggest using a script to restore data, unless it is a production system that doesn't change very often. For a consumer desktop I recommend, and this is my latest recommendation:
Make /home on a separate partition from /. Make / about 15 GB. Then you can backup / to /home with dd. If you trash / with some slip of the finger as the root user, or like to experiment, no matter what you do you can always boot with the http://www.efense.com/helix CD and write the backed up, known good / back from /home/sam to /. If you always do a backup:
I like the idea of being able to use dd to regenerate/rejuvenate a hard drive, so I whipped up this little script to automate the process a bit, with some basic sanity checks......Comments/feedback welcome....
regenhdd
Code:
#! /bin/sh
#
# regenhdd : Regenerate/rejuvenate hard drive by rewriting all data back onto
# itself. Restores possible data loss on unused drives.
#
### SANITY CHECKS
# Commandline check:
if ! [ $# -eq 1 -o -b "${1}" ] ;then
echo -e "\tUSAGE: ${0} <block_device>" >&2
echo -e "\t NOTE: Device must be a valid block device, such as '/dev/hda'." >&2
exit 1
else
DEV=$1
fi
# Check for mounted partitions:
if grep -q "${DEV}.\+rw" /proc/mounts ;then
echo -e "Please make sure all partitions on ${DEV} are not mounted, or at least mounted as read-only (ro) to avoid possible filesystem corruption." | fold -s >&2
echo -e "If this is the root filesystem ( / ), then drop into single-user mode (runlevel 1) and make sure the filesystem is mounted as read-only. Even better, reboot to a live cd/usb stick and run this program from there." | fold -s >&2
exit 1
fi
### Time to go to work
echo "Regenerating block device, ${DEV}. This may take a while..."
nice dd if=${DEV} of=${DEV} || exit $?
echo 'Done!'
exit 0
Can you use the dd command on Live CDs or Live DVD's such has Knoppix 5.1.1?
If so, is it any different than using dd on installed distros?
Do devices mount in a different folder on Live CDs/DVDs?
If so, in what folder do the devices mount?
I ask all of these questions because I am trying to image my HDD hda1, MBR and all, to my external HDD "sdb2" and save the output as an image(.img).
Again, I am using Knoppix 5.1.1 DVD
Thanks
Dd works the same way on a live CD as it does from a hard drive installation. You didn't mention any problems, but I'm guessing your external drive might not show up in Knoppix. You can try hotplugging it, and then do:
dmesg | tail
pretty quickly after you plug in the external hard drive. The other problem might be file system dependant. Certain file systems only allow 2 GB files, and certain other ones only 4 GB files.
The only problem is that the page is stretched out horizontally.
The first DIV contains:
dd if=<source> of=<target> bs=<byte size>("USUALLY" some power of 2,...
So to read each line, I have to keep scrolling back and forth. This is very annoying and distracting.
I suggest the width of the DIV be reduced to 790px.
Well, I finally tested this DD thing to clone a hard drive. The command I used was:
# dd if=/dev/sda of=/dev/sdb conv=notrunc,noerror
Once the cloning was done, I unplugged the original drive, and left the newly cloned drive in.
It booted up great, and everything seemed ok, like the original drive.
Unfortunately the command,
# crontab -e
gave me the error:
cron/root: Input/output error
I don't know what this error means, or how to fix it.
So, I assumed the drive was bad.
So I removed the supposedly bad drive, put in another blank drive, hooked up the original drive, and repeated:
# dd if=/dev/sda of=/dev/sdb conv=notrunc,noerror
This time, the cloning didn't give the error above. The cloned drive seems to be an exact copy of the original.
The only problem is that the page is stretched out horizontally.
The first DIV contains:
dd if=<source> of=<target> bs=<byte size>("USUALLY" some power of 2,...
So to read each line, I have to keep scrolling back and forth. This is very annoying and distracting.
I suggest the width of the DIV be reduced to 790px.
Well, I finally tested this DD thing to clone a hard drive. The command I used was:
# dd if=/dev/sda of=/dev/sdb conv=notrunc,noerror
Once the cloning was done, I unplugged the original drive, and left the newly cloned drive in.
It booted up great, and everything seemed ok, like the original drive.
Unfortunately the command,
# crontab -e
gave me the error:
cron/root: Input/output error
I don't know what this error means, or how to fix it.
So, I assumed the drive was bad.
So I removed the supposedly bad drive, put in another blank drive, hooked up the original drive, and repeated:
# dd if=/dev/sda of=/dev/sdb conv=notrunc,noerror
This time, the cloning didn't give the error above. The cloned drive seems to be an exact copy of the original.
The only thing dd can do for a drive with I/O errors is write zeroes to every sector. Then one needs to use a hard drive utility from the drive manufacturer's web site to relocate the bad sectors.
Hi,
I found the answers to many of my questions. thank you very much.you are a very good teacher.
Here is one of my problems with my home network and its internet connection sharing. Maybe you could help me to solve my problem.
1- I have a xp(windows) which is connected to internet using a dialup modem,I owuld like to set it up as a gateway (proxy) for my linux (redhat9) machine to access the internet.
2- my second question is exaxctly vise versa, I have a redhat9 installed pc which is connected to internet using a dialup modem and I would like to set it up as a gateway for my xp(windows) machine to access the internet.
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I/O error is almost always the drive hardware.
