Linux

Most operating systems have a mechanism to upgrade the existing version into a newer one. In most cases even thinking about upgrading without a fresh install-as-new makes me puke. The upgrade process is always complex and missing something while at it is more than likely to happen. These misses typically aren't too fatal, but may make your system emit weird messages while running or leave weird files into weird subdirectories. I run my systems clean and neat, so no leftovers for me, thanks.

There are two operating systems, which are exceptions to this rule of mine:
Windows 10 is capable of upgrading itself into a newer build successfully (upgrading a Windows 7 or 8 into a 10 is crap, do that to get your license transferred, then do a fresh install) and openSUSE. Upgrading a macOS is kinda working. It does leave weird files and weird subdirectories, but resulting upgraded OS is stable. Other Linuxes then openSUSE are simply incapable doing doing a good enough job of upgrading and I wouldn't recommend doing that. They'll leave turd, residue and junk behind from previous install and the only reasonable way is taking backups and doing a fresh install. openSUSE engineers seem to have mastered the skill of upgrade to my satisfaction, so that gets my thumbs up.

As openSUSE Leap 15.2 saw daylight on 2nd July, I felt the urge to update my Mac Book Pro into it. Some stories about my install of 15.1 are available here and and here.

The system upgrade of an openSUSE is well documented. See SDB:System upgrade for details.

To assess what needs to change, run zypper repos --uri and see the list of your current RPM-repositories. Pretty much everything you see in the list will have an URL with a version number in it. If it doesn't, good luck! It may or may not work, but you don't know beforehand. My repo list has something like this in it:

#  | Alias                     | Name                              
---+---------------------------+-----------------------------------
 2 | google-chrome             | google-chrome                     
 3 | home_Sauerland            | Sauerland's Home Project (openSUSE
 4 | openSUSE_Leap_15.1        | Mozilla Firefox                   
 5 | packman                   | packman                           
 6 | repo-debug                | Debug Repository                  
 7 | repo-debug-non-oss        | Debug Repository (Non-OSS)        
 8 | repo-debug-update         | Update Repository (Debug)         
 9 | repo-debug-update-non-oss | Update Repository (Debug, Non-OSS)
10 | repo-non-oss              | Non-OSS Repository                
11 | repo-oss                  | Main Repository                   
12 | repo-source               | Source Repository                 
13 | repo-source-non-oss       | Source Repository (Non-OSS)       
14 | repo-update               | Main Update Repository            
15 | repo-update-non-oss       | Update Repository (Non-Oss)       

What I always do, is a backup of the repo-configurations. Commands like this run as root will do the trick and create a file repos-15.1-backup.tar into /etc/zypp/repos.d/:

# cd /etc/zypp/repos.d/
# tar cf repos-15.1-backup.tar *.repo

Next, upgrade versions in the static URLs with a carefully crafted sed-run:

# sed -i 's/15.1/15.2/g' /etc/zypp/repos.d/*.repo

A non-static .repo-file (example: /etc/zypp/repos.d/repo-oss.repo) will contain something like this:

[repo-oss]
name=Main Repository
enabled=1
autorefresh=1
baseurl=https://download.opensuse.org/distribution/leap/$releasever/repo/oss/
path=/
type=rpm-md
keeppackages=0

Notice the variable $releasever. No amount of editing or running sed will change that. Luckily there is an easier way. Run zypper with an argument of --releasever 15.2 to override the value of the variable. More about repository variables like $releasever are in documentation https://doc.opensuse.org/projects/libzypp/HEAD/zypp-repovars.html. zypper arguments are in the man page at https://en.opensuse.org/SDB:Zypper_manual_(plain).

Additional:
As my system is depending on stuff found in Sauerland-repo, I did this to upgrade the entries:

# zypper removerepo home_Sauerland
# zypper addrepo https://download.opensuse.org/repositories/home:Sauerland/openSUSE_Leap_15.2/home:Sauerland.repo

Now all the repo URLs are set. As documented doing some preparations:

# zypper --gpg-auto-import-keys ref
# zypper --releasever 15.2 refresh

Finally going for the actual distro update:

# zypper --releasever 15.2 dist-upgrade --download-in-advance

This will resolve all conflicts between old and new packets. If necessary you'll need to decide a suitable course of action. When all is set, a lengthy download will start. When all the required packets are at your computer, following prompt will be presented for you:

The following product is going to be upgraded:
  openSUSE Leap 15.1  15.1-1 -> 15.2-1
The following 7 packages require a system reboot:
  dbus-1 glibc kernel-default-5.3.18-lp152.20.7.1 kernel-firmware libopenssl1_1 systemd udev

2210 packages to upgrade, 14 to downgrade, 169 new, 54 to remove, 2 to change arch.
Overall download size: 1.40 GiB. Already cached: 0 B. After the operation, additional 475.5 MiB will be used.

    Note: System reboot required.
Continue? [y/n/v/...? shows all options] (y): y

Going for a Yes will start the actual process:

Loading repository data...
Reading installed packages...
Warning: You are about to do a distribution upgrade with all enabled repositories. Make sure these repositories are compatible before you continue. See 'man zypper' for more information about this command.
Computing distribution upgrade...

When everything is done, following message will be displayed:

Core libraries or services have been updated.
Reboot is required to ensure that your system benefits from these updates.

This is your cue. Reboot the system.

If your upgrade went ok, you'll end up in a successfully upgraded system. To confirm the version of openSUSE, you can as an exmple query which package owns /etc/motd:

# rpm -q -f /etc/motd

The expected answer should be something like: openSUSE-release-15.2-lp152.575.1.x86_64

Also, second thing you need to verify is the version of Linux kernel your system is running with a:

# cat /proc/version

In openSUSE Leap 15.2 you'll get something like: Linux version 5.3.18-lp152.20.7-default (geeko@buildhost). If your kernel version isn't in the 5.3-series, something went wrong. 15.2 will use that. If you see that version, you're golden.

Congratulations! You did it!

Quite fast and painless, wasn't it?