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Re: Debian 8 and Debian 9 Dual Boot

On 11/13/17 07:26, Dan Norton wrote:

On 11/13/2017 01:10 AM, David Christensen wrote:

1.  Image, backup, and/or archive everything.  You will especially want to get a copy of the /etc tree onto a USB flash drive so you can see LVM, fstab, etc., configuration settings for mounting the Debian 8 disk under Debian 9.

Please say more about the configuration settings. I back up /home and /var. The git stuff is in /opt and pushed to GitHub. Should the /etc tree be backed up also? How would the settings be used from 9?

Every operating system and every software application installed on that operating system has configuration settings. One of the advantages of the traditional Unix model is that most OS settings are in plain text files that you can change with a text editor. Similarly so for server applications. (Desktops and their applications are another story, see below.) Good software has manual pages that explain where its configuration files reside and the format and meaning of the contents. Debian and Debian-ized applications seem to put most of their configuration files under /etc.

Whenever I decide to change such files, I make a copy with '-orig' appended, put the original file into a version control system (CVS), edit-test-repeat, and check-in to CVS when done. On a typical workstation, I might have a dozen files under /etc checked in. On a server, more.

I once tried putting the entire /etc directory into CVS. Adding and removing software made a lot of changes, as expected. But, so did normal operations. Locating meaningful changes in became an exercise in "find the needle in the hay stack". And, adding/removing lots of files and directories in CVS working directories is labor intensive. I don't do that any more.

For migrations, unless you are an expert already or psychic, you will want the old drive in it's entirety. (I keep my system drives under 16 GB, to encourage me to take images at opportune moments like this.) It's useful to also copy /etc onto a flash drive when your old drive is more complex than a partition table and normal file systems (so that you will have clues about how to mount it, for starters).

As for how the settings are used, each OS instance and it applications determine that. Migrating settings involves editing configuration files and/or overwriting configuration files. You have to go through each subsystem one at a time and see what configuration files it wants, format, and content, and then do what it takes to make it happy.

As others have replied, desktop and desktop application configuration settings and data in home directories are not agreeable to migration. I don't even try. I backup Thunderbird mail and export address books on the old system, and restore/ import on the new system. I use the sync service built into Firefox to keep it current on all my machines where it is installed. I check in my CVS working directories on the old system and check them out on the new system. My bulk data is on the file server. I manually configure whatever is left -- desktop, Open Office preferences, etc..

2.  Put your bulk data onto a separate drive or a file server/ NAS.

3.  If your computer has a spare drive bay, buy a new drive, unplug your old drive, install the new drive, install Debian 9 onto the new drive, reconnect the old drive and mount read-only under Debian 9, and migrate your settings and remaining data from the old drive to the new drive. Your BIOS/UEFI should allow you to boot from either drive during this process.  So long as you don't damage the Debian 8 disk, you can always fall back to Debian 8 if the migration goes badly.

4.  If you computer does not have a spare drive bay, buy a new drive and a USB external drive enclosure, put your old drive in the enclosure, install the new drive, install Debian 9 onto the new drive, plug in the old drive and mount read-only under Debian 9, and migrate your settings and remaining data from the old drive to the new drive. Again, your BIOS/UEFI should allow you to boot from either drive and you can fall back to Debian 8 if necessary.

Sobering advice - good! Makes me re-think some things. A bit inefficient WRT disk space.

Disk space is far cheaper than data loss. Don't make the mistake of trying to save money through partition, LVM, file system, etc., gymnastics rather than simply buying another drive and doing it the KISS way.

You did say "migrate" and not "upgrade" as I first read. Thanks David.

YW.  :-)


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