Running Systems

On most cases, when preparing a recovery server, you can just ‘tar’ the entire server’s contents and just move it, along with a short recipe on how to rebuild the original partition layout (software Raid? LVM? flat partition tables?), how to mount volumes in-place, how to extract the tar files into the right locations, and how to install your favorite boot loader, either Lilo or Grub. Also, beforehand, you deal with taking a nice snapshot (or capturing the system in a single-user phase), and life is good, yada yada yada.

Most of us, however, never prepare for a rainy day. It’s not that we don’t want to, it’s not that we don’t plan, it’s just that we never seem to get to it, and after all, the hardware is rather new, and there should be no reason for failure. I can guess some of you heard this before – maybe in their own voices.

So, backup is a tiring job, and I will not deal with the things you need to do to maintain a replica of your data, but I will deal with how to prepare, quickly and easily, a system-recovery server (or a postmortem server) with just a little thought beforehand. This might be a bit too late for you if you’re reading it now, but, well, for the next time…

This little trick worked (as part of a large-scale process) when I migrated a server from 64bit server to a 32bit server (yeah, I know – the other way around).

It assumes you use RPM as your tool to install applications, and that if you do not, you have a method of knowing which piece of software you installed from source, and which package was installed from an external source (not your day-to-day RPM repository).

On the source server, run ‘rpm -qa > /tmp/rpmlist.long‘. Keep this file. It is important. Also, try to keep your yum.repos.d directory, or at least know which rpm repositories you use (I always use rpmforge, so I see no problem with that).

Install your target server – Same version as the source, minimal package selection. Copy the file rpmlist.long to /tmp. Make sure yum is configured (I will deal here with YUM, but you can replace it with any other repository client of your choice). Run the two following lines:

cat /tmp/rpmlist.long | sed s/-[0-9].*$/”/g > /tmp/rpmlist-short

for i in `cat /tmp/rpmlist-short`; do

yum install -y $i

done

This will add the missing RPMs with their dependencies, and will bring your system to a similar status. At least, this is a good place to start recovering.

On future chapters:

– Fully migrating from 64 to 32 bit and vice versa

– Using LVM snapshots for a smart backup, and for a smart recovery