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I have two Debian 9 servers, server A and Server B.

Server A is a LAMP stack server.

Server A is slow. Server B is fast.

I want to clone server A to server B without shutting down server A.

How do I do that?

I think I can do something like this:

  1. Install Debian 9 on server B as a base installation
  2. use rsync to copy over all of /home/ from A to B, then copy over /etc/passwd, /etc/groups, and /etc/shadow
  3. Dump the packages that are installed on A, create a script to install those on B.
  4. Dump the MySQL databases from A, copy to B, and import
  5. Copy over the contents of /etc/ with rsync.

Or... could I just rsync the ENTIRE server from B to A?

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Please read over each link carefully before attempting any commands.

I have used this rsync example by user ericslaw to successfully clone my working Linux install to a different drive.

You can mount a remote or local target file system to /mnt of your source file system. As root(sudo) run the following:

mount /dev/sdb1 /mnt

/dev/sdb1 is your second server disk. It can be remote or local, whatever works best for you.

rsync -gloptruncv \
      --exclude={/dev/*,/proc/*,/sys/*,/tmp/*,/run/*,/mnt/*,/media/*,/lost+found} \ 
      / /mnt 

This will be a dry run. If there are no errors then you should be good to go to exclude the n option. After which you need to follow the advice in this post. After your back up has completed ( You can even use their options instead depending on your circumstances) Then reset /mnt/etc/fstab for the boot and swap partitions. I highly recommend these entries are based on the UUID of the block devices. blkid will tell the information you need. After fstab is fixed you need to run grub-install /dev/[serverB disk] to be able to boot. Alternatively you can chroot into the backup and install grub that way.

 chroot /mnt
 grub-install --recheck /dev/sdb1
 update-grub

Lastly you may need to recreate the missing folders of your backup (/dev/, /proc/, /sys/, /tmp/, /run/, /mnt/, /media/, and /lost+found).

This can also be done in reverse. Have Server B mount Server A's disk and then sync non system files between the two. This is easiest if Server A and B are running the same version of the same distro.

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