Upgrading a hosted Debian 8 VM to Debian 9

A long time ago, I extolled the virtues of Cloud at Cost’s developer cloud. It’s a good tool for spinning up a box to mess with, but it’s far from being reliable enough for “production” use. What it is great for is having a box that isn’t constrained by a network (like a VM at work might be), but for which access to it may require modifications to a local firewall (like a VM at home might be), while avoiding the cost of a “real” production VM on Digital Ocean or Amazon.

Using a VM this way is a bit like building your house out of straw. It goes up fast, but it comes down fast too. So I have gotten used to setting up machines quickly and then watching them be corrupted and blowing them away.

Sometimes I do something stupid to corrupt them, sometimes they go corrupt all on their own.

The base Debian install on C@C is getting a bit long in the tooth, so part of my normal setup is now upgrading Debian 8.something all the way to Debian 9.whatever. This procedure will take a pretty long time. A long enough time that you will probably have to leave home to go to work, or vice versa. I recommend locking down SSH and then installing screen so you can attach and detach sessions that are running in the background.

Step 1 – update your sources and update your current version:

First, you should check your version of Debian, to make sure that you are on some version of Jesse, and not an earlier version for some reason:

# cat /etc/debian_version

The sources on a brand new C@C Debian 8 box are woefully out of date. Use your favorite editor (mine is nano; fight me) to edit the sources list.

# nano /etc/apt/sources.list

### Remove the entries and paste these in ####
deb http://httpredir.debian.org/debian jessie main
deb http://httpredir.debian.org/debian jessie-updates main
deb http://security.debian.org jessie/updates main

Once you have the list updated, save the file and run the upgrade scripts like so:

# apt-get update
# apt-get upgrade
# apt-get dist-upgrade

On a new install this will take a long time. Note that if you are having trouble installing screen or fail2ban, you probably have to do this step before installing them.

Step 2 – See how bad the damage is

Now we see what kind of hell we will be unleashing on this poor little machine by upgrading just about everything. First, see what packages are broken:

# dpkg -C

On a fresh debian 8 box, there shouldn’t be a lot to report. If there is you need to fix those packages. Assuming that you got no messages about messed up packages, you can see what’s been held back from upgrade like so:

# apt-mark showhold

If you got a message that packages are obsolete, you can remove them like so:

# apt-get autoremove

Hopefully you don’t have any messed up packages, and you can proceed to the next step.

Step 3 – Do the thing

Now it’s time to change the sources from Jesse to Stretch and basically do step 1 all over again.

First you update the sources.list file:

# nano /etc/apt/sources.list

### Remove the entries and paste these in ####
deb http://httpredir.debian.org/debian stretch main
deb http://httpredir.debian.org/debian stretch-updates main
deb http://security.debian.org stretch/updates main

And then tag packages to be updated:

# apt-get update

Now do a dry run to see if it will blow up or not:

# apt list --upgradable

Assuming there are no flashing red lights or whatever it’s time to pull the trigger.

Step 4 – Hold on to your butt

Once you run the next set of commands, you will be asked if you want to restart services without asking. Assuming that you are doing this in screen, you can lose your SSH connection and the process will still run. In the event of a catastrophic failure, you can probably open the console and attach to your screen session, so say yes and then buckle up.


# apt-get upgrade
# apt-get dist-upgrade

This will take a long time. Like a really long time. It’ll look cool tho. Having a command line window with text rolling by always makes me feel like Neo from the Matrix.

Step 5 – ??? Profit

Once it’s done, check the Debian version and revel in your victory:

# cat /etc/debian_version

Then check for obsolete packages, for which there will probably be a bunch:

# aptitude search '~o'

And then finally remove them all, like so:

# apt-get autoremove

Just to be safe, you should probably update and upgrade one last time:

# apt-get update
# apt-get upgrade

Step 6 – Diversify your backups

Now that you have gone through all of the difficulty of upgrading your house made of straw, it would be a shame for a big bad wolf to blow it down. For this reason, I recommend an old school Unix backup with tar, and keeping a copy of your backup on another computer. For this second part we will be using scp, and I recommend setting up SSH Keys on another Unix host. This might be a good time to set up ssh key pairs without passphrases for your root accounts to use.

The security model looks something like this:

  1. No one can log into any of the hosts via SSH as root.
  2. No one can log into any of the hosts without a private key.
  3. Your plain user account’s private key should require a passphrase.
  4. Your root password should be super strong, probably randomly generated by and stored in password manager like KeePass.
  5. If you want to scp a file as root without a passphrase, you should have logged in as a plain user with a private key with a passphrase and then used su to become root.
  6. If you can get past all those hurdles, a second public key passphrase isn’t going to protect much.

Change to the root of the file system (/) and run a giant compressed backup job of the whole filesystem (except for the giant tarball that you are dumping everything into).

# cd /
# tar -cvpzf backup.tar.gz --exclude=/backup.tar.gz --one-file-system / 

This will also take a long time, so you should seriously be using screen. Also, there is a lot of stuff in the backup that doesn’t actually need to be backed up, so you could add additional –exclude=/shit/you/dont/need statements to shrink the size of your backup file.

Once once the backup is done you can then change the name of the backup file to that of your machine name and use SCP to copy off the backup file to another Unix host. In the example below I am calling the backup randoVM. You should change the name because you may be backing up multiple VMs to the same source. I like to use my HUB VM at home because it has a lot of [virtual] disk space compared to my hosted VMs.

# mv /backup.tar.gz /ranoVM.tar.gz
# scp randoVM.tar.gz steve@home.stevesblog.com:~/backups/ranoVM.tar.gz 

You can leave the big tarball on your VM’s file system, or you can delete it. There are merits to doing either. You will want to repeat this backup procedure periodically as you add features and services to the VM.

If you find yourself needing to restore the VM because you or the big bad wolf did something stupid, you can simply pull the backup down and expand it.

# cd /
# scp steve@home.stevesblog.com:~/backups/ranoVM.tar.gz .
# tar -xvpzf ranoVM.tar.gz

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