Linux System Duplication
Andrew McGill, ledge.co.za
Revision 0.3; $Id: systemduplication.sgml,v 1.10 2006/11/16 07:58:08 andrewm Exp $Step by step instructions for duplicating a Linux system by copying the files from one hard disk to another.
1. Introduction
You may need to duplicate your Linux system onto another hard disk for any number of reasons, including:
- You have just replaced your hard disk with a newer, bigger or more reliable one
- You have a new computer
- You tried it with Ghost, and it messed up. You would like to mess it up yourself.
- You want to change the filesystem type you are using (e.g. reiserfs to ext3fs)
1.1 Assumptions
The following assumptions have been used in this document to simpify things (for the author, and not so much for the reader):
- The original, working system resides on a single IDE disk (e.g. hda)
- A second disk is available for copying the system to (e.g. hdc)
- You can type commands fairly accurately (no dyslexia)
- You can think and adapt if your system is a little different
- You want to duplicate your system
1.2 Introduction to the method
- Do some research (
mount; fdisk -p /dev/hda
) - Set up second system's drive on /dev/hdc
- Create similar partitions on the new disk hdc (fdisk /dev/hdc)
- Format the new partitions (mke2fs / mkreiserfs / mkswap /dev/hdc99)
- Mount the new disk on /mnt (mount /dev/hdc3 /mnt) and create mount directories in /mnt and mount the new file systems there
- Copy the files (cp -vax /. /mnt ... or something similar) (don't try cp -vax /* /mnt - it's not the same)
- Shutdown the system
- Install the hard disk (hdc) in a new system (it won't work yet)
- Boot the new system using a rescue disk (or something)
- Run lilo, reboot and test
1.3 Disclaimer
You will destroy your data. Don't blame me.
2. Research
Short version: Make notes of the partitions on your existing disk
Before you can copy a system, you need to know how big the various partitions are. Write down the output of one of the commands below. (fdisk is more useful if your new disk is the same as the old, and df is more useful at other times). The output of grep will show where your partitions should be mounted.
You may have a disk with SCSI or SATA drives. In this case the drives are named
fdisk -p /dev/hda
df -hl
mount
grep hd /etc/fstab
/dev/sda
, /dev/sdb
etc, and the partitions are named /dev/sda1
, /dev/sda2
, /dev/sda3
, etc. On my system with a 12G drive, the output looks like this:
tonto:~ # fdisk -l /dev/hda
Disk /dev/hda: 255 heads, 63 sectors, 1467 cylinders
Units = cylinders of 16065 * 512 bytes
Device Boot Start End Blocks Id System
/dev/hda1 * 1 255 2048256 c Win95 FAT32
/dev/hda2 256 264 72292+ 82 Linux swap
/dev/hda3 265 776 4112640 83 Linux
/dev/hda4 777 1467 5550457+ 5 Extended
/dev/hda5 777 777 8001 83 Linux
/dev/hda6 778 1467 5542393+ 83 Linux
tonto:~ # df -h
Filesystem Size Used Avail Use% Mounted on
/dev/hda3 3.9G 3.7G 262M 94% /
/dev/hda5 7.6M 5.7M 1.5M 79% /boot
/dev/hda6 5.3G 4.7G 700M 88% /data
shmfs 58M 0 57M 0% /dev/shm
/dev/hda1 1.9G 1.6G 399M 80% /windows/C
tonto:~ # mount
/dev/hda3 on / type reiserfs (rw)
proc on /proc type proc (rw)
devpts on /dev/pts type devpts (rw,mode=0620,gid=5)
/dev/hda5 on /boot type ext2 (rw)
/dev/hda6 on /data type reiserfs (rw)
shmfs on /dev/shm type shm (rw)
usbdevfs on /proc/bus/usb type usbdevfs (rw)
/dev/hda1 on /windows/C type vfat (rw,noexec)
tonto:~ # grep hd /etc/fstab
/dev/hda1 /windows/C vfat noauto,user 0 0
/dev/hda5 /boot ext2 defaults 1 2
/dev/hda2 swap swap defaults 0 2
/dev/hda3 / reiserfs defaults 1 1
/dev/hda6 /data reiserfs defaults 1 1
(it's a wonderfully bad example, since it includes a Windows filesystem). The thing to take note of is the size of the partitions (how many megabytes M or gigabytes G) and their locations. You will be creating identical partitions on your new disk.
3. Playing with hardware I
Short version: Plug in new hard disk into old machine
This howto works on the assumption that your system is configured something like the following: (or that you are smart enough to figure out what to do)
Primary IDE channel: Master : /dev/hda Original system
Slave : /dev/hdb CDROM or unused
Secondary IDE channel: Master : /dev/hdc Duplicate system
Slave : /dev/hdd Unused
If you plug the duplicate hard disk into /dev/hdb instead of /dev/hdc, then you will need to set the jumpers on the hard disk for it to act as a "Slave" and not as a "Master". Copying data between disks on separate interfaces could make things work a little faster though.
4. Create similar partitions
Short version: fdisk /dev/hdc; (d)elete existing partitions and make (n)ew paritions using (t)ype 82 and 83.
Fdisk is a tool that edits the first part of the disk, which is called the partition table. This determines how the space on the disk is allocated.
The resources for using fdisk are the fdisk man page, and the output of the help command when you run fdisk:
man fdisk
fdisk /dev/hdc
Command (m for help): m
Here's the procedure:
- Make sure you are using the correct disk (/dev/hdc, not /dev/hda)
fdisk /dev/hdc
- Test how to escape - press Ctrl+C to stop fiddling the partition table.
- Delete the existing partitions
You may have to delete the `logical' partitions before you delete the extended partitionp # Print the existing partition table
d # Delete a partition - Create new partitions of the correct sizes. Use the same numbers as before. To create partitions with a number greater than 4, create an extended partition, and then create additional "logical" partitions.
n # new partition
Command (m for help): n
Command action
l logical (5 or over)
p primary partition (1-4)
p # primary partition
Partition number (1-4): 1
First cylinder (1-1467, default 1): 1
Last cylinder or +size or +sizeM or +sizeK
(1-255, default 255): 255 - Set the type of the new partitions you have created. For Linux partitions, you will want to set the type to Linux (83) for the data partitions, and to Linux swap (82) for the swap partition(s).
Command (m for help): t
Partition number (1-6): 1
Hex code (type L to list codes): 83
Changed system type of partition 1 to 83 (Linux) - Have a look at the new partition table (it should look something like the one on the original disk)
If you are happy with what you see, write it to the disk:p
If fdisk complains that it cannot convince the kernel to reload the new partition table, you will have to reboot the system. This is normally a bad sign though, because there is no reason you will see this on an unused disk:w
If you inadvertently overwrote your original system's partition table, you should be able to recover by using the tool gpart (guess partitions) which is found on most rescue disks. Alternatively you can simply re-enter the same partition information as you had previously. Note that some systems have a menu driven program called cfdisk. If you like menu driven programs, you can give it a try, but don't blame me. When all is done, if it is done correctly, then these commands should produce similar output:Calling ioctl() to re-read partition table.
WARNING: Re-reading the partition table failed with error
16: Device or resource busy. The kernel still uses the
old table. The new table will be used at the next reboot.
Syncing disks.fdisk -p /dev/hda
fdisk -p /dev/hdc
5. Format the new partitions
Short version: mke2fs or mkreiserfs and mkswap
If the output of
looks like this:
grep hd /etc/fdtab
/dev/hda1 /windows/C vfat noauto,user 0 0
/dev/hda5 /boot ext2 defaults 1 2
/dev/hda2 swap swap defaults 0 2
/dev/hda3 / reiserfs defaults 1 1
/dev/hda6 /data reiserfs defaults 1 1
Then these are the commands that you will use to `format' the new partitions: There is an IMPORTANT change here! All of the partitions are being created on the NEW drive /dev/hdc, not on the old drive. Don't get it wrong, or you will delete the system you are trying to duplicate.
There is also
mkfs.ext2 /dev/hdc4
mkswap /dev/hdc2
mkfs.reiserfs /dev/hdc3
mkfs.reiserfs /dev/hdc6
mkfs.ext3
which makes ext3
format filesystems. We won't need the Windows partion on the new system :) ... but if we did for some reason, it would be safer to get Windows to do it with its own format command.
6. Mount partitions
Mount the root partition of the new system on the /mnt point:
mount /dev/hdc3 /mnt
Create directories in this system for each of the mount points it will use. On my system, this means three directories (although you probably won't have all of these)
mkdir -p /mnt/boot
mkdir -p /mnt/windows/C
mkdir -p /mnt/data
Now mount the partitions on the directory mount points you have made:
Check your work. The output of `mount' should show similar entries for /dev/hda (point points based at /) and /dev/hdc (based at /mnt/).
mount /dev/hdc5 /mnt/boot
mount /dev/hdc3 /mnt/
mount /dev/hdc6 /mnt/data
7. Copy files
For each partition, copy all the files (see GOTCHA in endnotes). The copy command make exact(ish) archive (-a) copies, has a handy verbose mode (-v), and a `don't cross filesystems' option (-x), which we will use. Copy each of the partitions from the old system to the new system:
Alternatively, you can use tar to do the same thing. This is a better idea if you have sparse files (but if you are reading this howto, you might not know what those are...)
cp -vax /boot/. /mnt/boot
cp -vax /. /mnt
cp -vax /data/. /mnt/data
You have to specify each mount point, since the `l' option above tells tar not to cross between file-systems (similar to the `-x' option in cp).
cd /
tar clS / /data /boot | tar xv -C /mnt
Did I mention that if you have a database server or a mail server running you should stop it during the time that you copy its files? If you fail to do this on a relatively busy server, you may copy files which are in a particularly nonsensical state which they pass though during updates.
To be (relatively) sure that the data has been copied to the disk:
sync
That's it. Well, almost.
7.1 If you changed device names and file systems ...
You're one of those people who is doing this whole thing because you're migrating from ext3 to jfs (crazy!), from SCSI to IDE, and now suddenly your system doesn't boot because of kernel panics or something similar.
You need to edit files:
vi /mnt/etc/fstab
-- edit the filesystem table that says which devices should be put where.vi /mnt/etc/lilo
-- if your system is using LILO to boot, then make sure that the lineroot=/dev/sda8
points to the device your main partition (/.
) is on. If you've changed filesystem types, thenreiserfs
may change toext2
andjfs
so that the device names correspond again with the partition types they contain. After changing this file, runchroot /mnt
andlilo
again as described above.vi /mnt/boot/grub/menu.lst
-- if you're using GRUB as your boot loader, then this is where you need to change your device names.
vi
, here's a three point tutorial: - Press
i
to insert, andEscape
when you're finished inserting. - Type
ZZ
(capitals) to save and exit, orZQ
to exit without saving. - If in doubt, quit
vi
and run the commandvimtutor
to learn how to do it.
7.2 If you changed your disk controller ...
If you are using a different disk controller on the target system (e.g. sata_nv
to piix
), for most distributions, you will have to make a new initial root disk, using the mkinitrd
command. If you need to do this and you don't do this, you will get a kernel panic "cannot mount root filesystem".
You need to:
- Find out which module(s) the disk requires
- Tell
mkinitrd
to include it (or them) - Run
mkinitrd
on the target system to make a newinitrd
file for booting.
lspci
and lsmod
. As the kernel becomes more and more modular, it becomes harder to know which is your disk controller module. You can use modinfo piix
to see what a module says about itself: If you don't know, guess. It can't hurt that much.
modinfo piix
filename: /lib/modules/2.6.15-23-386/kernel/drivers/ide/pci/piix.ko
author: Andre Hedrick, Andrzej Krzysztofowicz
description: PCI driver module for Intel PIIX IDE
license: GPL
vermagic: 2.6.15-23-386 preempt 486 gcc-4.0
Now tell mkinitrd
to include the module:
- Debian/Ubuntu:
vi /etc/mkinitrd/modules
, then runupdate-initrd
. - SuSE:
vi /etc/sysconfig/kernel
, then runmkinitrd
. - Redhat ... erk ... suggestions welcome
8. Playing with hardware II
Now you have to get the new system to be bootable.
8.1 Method 1 (easy) (using rescue disk)
- Shutdown the original system.
- Remove the duplicate hard disk.
- Put the duplicate disk in the new system.
- Boot up the duplicate system using the rescue disk or rescue boot option provided by your Linux distribution. This should dump you at a shell prompt.
- Mount the root partition:
mount /dev/hda3 /mnt
- Enter the new system, mount additional filesystems (e.g. /boot), and run lilo to make the system bootable.
If you are using the GRUB boot loader, then instead of lilo, you typechroot /mnt
mount -a
lilogrub-install /dev/hda
to install GRUB on the MBR.On some distributions,
grub-install
is broken. For these you have to ...grub
root (hd0,0) # assuming /boot is /dev/hda1
setup (hd0)
quit - Now you can exit and shutdown:
umount -a
sync
exit
umount /mnt
reboot
Remove the disk and reboot. The system should boot as a duplicate.
8.2 Method 2 (best for GRUB) (hard, but you don't need a rescue disk)
If your system boots with GRUB, you can set up the second disk to be ready to boot when it becomes the first disk:
- Boot up the original system with the duplicate hard disk in (probably you are here already)
- Chroot into the new system.
- Lie to GRUB about where its hard disks are
- Install GRUB (on the second disk)
- Tell GRUB the truth again for posterity
Here's the detail:
- Mount the duplicated root partition:
mount /dev/hdc3 /mnt
- Chroot into the new system, mount additional filesystems (e.g. /boot):
chroot /mnt
mount -a - Now edit
/boot/grub/device.map
, and tell it that the first disk is your duplicate disk (/dev/hdc):
Change the contents of device.map from this ...cd /boot/grub
cp device.map device.map.foo
vi device.map.foo
... to this...(hd0) /dev/hda
(hd0) /dev/hdc
- Now, tell GRUB to install itself. GRUB's device naming is funny, but you have to give the partition number-1. If your duplicated root partition is
/dev/hdc7
, then the name to give GRUB is(hd0,6)
. Here's how you run grub and get it to install: you start GRUB, using the device map file that says what the BIOS drive number will be after we swap the disks ...grub --device-map=device-map.foo
root (hd0,6)
setup (hd0)
quit
8.3 Method 3 (best for LILO) (hard, but you don't need a rescue disk)
If your system boots with LILO, you can set up the second disk to be ready to boot when it becomes the first disk:
- Boot up the original system with the duplicate hard disk in (probably you are here already)
- Chroot into the new system.
- Lie to LILO about where its hard disks are
- Install LILO (on the second disk)
- Tell LILO the truth again for posterity
Here's the detail:
- Mount the duplicated root partition:
mount /dev/hdc3 /mnt
- Chroot into the new system, mount additional filesystems (e.g. /boot):
chroot /mnt
mount -a - Now edit
/etc/lilo.conf
, and tell it that the first disk is your duplicate disk (/dev/hdc). You need to add this data:disk=/dev/hdc
bios=0x80
disk=/dev/hda
bios=0x80 - Now, tell LILO to install itself on the new hard disk.
lilo -b /dev/hdc
lilo.conf
on the new disk, but you could happily leave them there too. 8.4 Method 4 (easier, but more likely to fail) (actually, 100% likely)
This method involves booting up off a floppy disk. The only problem is that you cannot use an initial root disk (initrd), which may make scsi and reiserfs and ext3 systems fail. Actually, it's not very likely to work at all Actually, it's not very likely to work at all. It won't work. Do this if you're desparate.
Create a boot disk containing the Linux kernel:
dd if=/boot/vmlinuz of=/dev/fd0 bs=18k
Set the root partition
rdev /dev/fd0 /dev/hda3
- Shutdown the original system.
- Remove the duplicate hard disk.
- Put the duplicate disk in the new system.
- Boot up the duplicate system using the kernel disk you made.
- It should boot as a duplicate of the original system.
- Login as root and install lilo:
lilo
9. History
Version 0.1: Thanks to Brett Geer for pointing out that cp -vax /* /mnt is wrong. That was not pretty.
Version 0.2: Added some GRUB data ... and a bit of fstab and menu.lst notes.
Did I mention you will destroy your data?
Someone from Spain says there's a "mistake mounting partitions", but didn't elaborate. So be careful there.
Gotcha: Newer systems may mount a temporary filesystem over /dev
for devfs or udev. This causes cp -a
to be incomplete, and the result is an unbootable system (missing /dev/console
). To avoid this, the root filesystem of the source must be remounted somewhere where the real contents of /dev
are not hidden. That's a TODO.
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