Tag Archives: Leap 15.2

Upgrade of a server host from Opensuse Leap 15.1 to 15.2 – I – a problem with Apache2/MPM and PHP7

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The official support of Opensuse Leap 15.1 is about to end. Time to upgrade some servers to Opensuse Leap 15.2 in my home-office. While the basic upgrade of the OS was a smooth process I stumbled across some problems and challenges with a few services. I shall cover these problems step by step in this series – and hope that my remarks and hints will help some of my readers.

A central server system with network related services and with virtualized guests

One of the two central server systems in my LAN provides DHCP-, DNS-, OpenLDAP-services plus an internal HTTP-service (based on Apache2) for development work. Its list of services in addition comprises NFS, Samba and some SVN-services for multiple purposes, among others as backup space for other systems. The host also works as a CUPS server – offering some pre-defined queues for other Linux-systems in the LAN.

The system also serves as a KVM- and LXC-host for some virtualization guests: A KVM based LAMP/GIT-server for production data, a KVM based mail-server, a KVM based Kali-system plus some LXC-containers for databases. Some LVM volumes on this server are encrypted and all disk-space is based on Raid configurations – both with mdadm for different SSD-raids and with a 3ware controller for a standard hard disk based raid10. This server is also critical as it separates its internal virtual network structure from real LAN segments by a packet-filter. It must cover routing tasks.

I run this Linux host with Opensuse Leap – not SLES. So, it is a good test object for the cleanliness of Opensuse’s upgrade practices. Actually, I am always a bit nervous during upgrade. Fortunately, the HW is from the time of my freelance business – and thus safe and proven to use. It contains a passively cooled Nvidia card, for which the community repositories still provides kernel modules. The 3ware drivers also have worked reasonably well over the last 4 years. So, drivers at least should not pose any problems.

To make a long story short: The basic upgrade did not cost me much headache. I outline the upgrade procedure below – and then turn to the problems I have seen in its wake.

Backup and basic upgrade procedure

It should be clear that a server as the described one requires some regular backup routine for important data. I shall not elaborate on this topic here. Regarding the backup of the “/”-partition I use an approach described in the article
Upgrade workstation from Opensuse Leap 15.1 to Leap 15.2:

I.e. I copied the whole partition to a different, external hard-disk and afterwards in addition to a free partition on the server system itself – all with the help of the “dd”-command. You may do the same with other partitions which you want to re-create quickly in case of an emergency during upgrade.

Regarding the upgrade itself I cling to the procedure described by the Linux Kamarada; see the article mentioned above. (The required work with the Opensuse repositories is much simpler for my servers than for my workstations and laptops as I use much less repositories; the only repositories aside the Update repository for the present Leap version are SUSE’s “Security” and “Network” repositories plus the Nvidia community repository. I have made good experiences with this habit over the last 10 years.)

The upgrade worked almost perfectly. Some quick checks verified that my virtualized (and not yet upgraded) virtual guest systems could be started and worked as expected. The same was true for the slapd-, smb-, the wsdd- and the dns- (=named-) service.

But, there were also exceptions which required additional work:

  • Graphics Failure: The X-system did not start and the “graphical target” of systemd could not be reached directly after the system
    upgrade (expected).
  • Service failure: The Apache2 service did not start (unexpected).
  • Service failure: The smartd-service did not start (unexpected, but probably due to an overwritten configuration file).
  • Required Adjustment: The CUPS libraries had to be changed to Opensuse’s “Printing” repository to become consistent with other Linux hosts which use printer queues on the server (expected).
  • Required Adjustment: The rkhunter-configuration had to be adjusted (expected).
  • Required Adjustment: A specific KDE-settings had to be adjusted to allow for screen-saving functions – even for SDDM screens without started KDE-sessions (unexpected).
  • Required Adjustment: “virt-viewer” access via “qemu+ssh” to some clients posed grave problems (unexpected). These problems may have existed already before, but are worth a description.

I cover the first 2 points in this article. Solving the graphics problem is a short story. The explanation and solution of the problem with the Apache service, however, requires some space. But I hope the information provided in the related text is interesting for some readers who are no experts in Opensuse’s handling of the Apache service.

Nvidia – X-Windows

You may ask: Why X11 on a server at all? Good question; well, as a semi-professional in server-administration, I think that one can do some things faster than without. Normally, I access the server remotely via ssh or “ssh -X”. But during my years with SLES and Opensuse I experienced some situations during which I was happy to be able to access the server directly on a graphical console; certainly not a popular view among profs. Anyway – the Nvidia/X-Window topic is a standard problem and easy to solve:

I just had to reinstall the required drivers from the Nvidia repository (via the CLI-based YaST), perform a “mkinitrd” afterwards and restart the system.

However, I nevertheless recommend not to boot the server system into the graphical systemd target, if not required. The relevant command to set the default target is

systemctl set-default multi-user.target

See the related link at the end of this post.

Off topic: If you prefer KDE as a graphical desktop environment do not even try to switch to Wayland on Leap 15.2. In my experience this is only a frustrating endeavor – as we still do not have Plasma 5.20 available but Plasma 5.18 (see a related link at the end).

Apache does not start due to a problem with “mod_php7” and MPM

Let us turn to something more interesting: An Apache problem with the current PHP-module and MPM-settings.

I admit, I am a bit old-fashioned. Most developers and admins, today, probably use Nginx and in addition Fast-CGI in combination with PHP. I, instead, cling to an old Apache installation for LAMP-services on the server named above. One reason is that I need some compatibility with things I did from 2013 and 2016 – aside of changes of PHP over the years.

So, whilst upgrading Opensuse my Apache 2.4 and PHP installations get upgraded, too.

When one activates the php-Apache-module by “a2enmod php” the presently installed version of the php-Apache-module gets loaded – on Leap 15.2 this is provided by mod_php7.so corresponding to PHP 7.4.6. (You can verify this with the command “php -v”). Using “a2enmod php7” would give you no different result. (Opensuse, unfortunately, does not support the parallel installation of multiple, different PHP-versions. See the critics in the conclusion-section.)

All upgrades from Leap 42.2 to 42.3, 15.0 and eventually to Leap 15.1 went well; but this time the Apache service did not start. Trying “rcapache2 start” followed by “rcapache2 status” (or equivalent systemctl status apache2.service) gave me an error message:

….
[php7:crit] [pid 16004:tid 139738320386304] Apache is running a threaded MPM, but your PHP Module is not compiled to be threadsafe. You need to recompile PHP.
Jan 26 19:15:39 MySRV start_apache2[16004]: AH00013: Pre-configuration failed
Jan 26 19:15:39 MySrv systemd[1]: apache2.service: Main process exited, code=exited, status=1/FAILURE
….

I remembered vaguely that I had experimented with MPM and prefork settings on Leap 15.1, but recompile PHP? With what options? A strange error message!

Confusion when comparing to a seemingly similar Apache2 installation on a different system

I cross-checked with a similarly configured Apache2 installation (with PHP7, but different virtual domains) on one of my my Leap 15.2 workstations; let us call it “MyWS” and the upgraded server “MySRV”. Confusingly, Apache2 started on MyWS without any complaints.

You may suspect now that I may have used different Apache2 configuration directives in “/etc/sysconfig/apache2” or the files in folder “/etc/apache2/” and sub-folders – without being aware of it. But no: I checked and eliminated even small, irrelevant differences for tests. The problem on the server MySRV remained.

When I looked at the Apache2-related processes on the workstation MyWS with “ps aux | grep https” I saw that Apache2 had been started in a pre-forked way. As I was used to …. I got multiple forked processes like 

....
wwwrun    7043  0.0  0.0 236180 10488 ?        S    10:41   0:00 /usr/sbin/httpd-prefork -DSYSCONFIG -DSSL -C PidFile /var/run/httpd.pid -C Include .... 
.....
wwwrun    7045  0.0  0.0 236180 10488 ?        S    10:41   0:00 /usr/sbin/httpd-prefork -DSYSCONFIG -DSSL -C PidFile /var/run/httpd.pid -C Include ... 
...

The interesting thing here is the indicated program “/usr/sbin/httpd-prefork”. Note that it is NOT “usr/bin/httpd”; I shall come back to this point later. The process information was of course consistent with startup information provided by “rcapache2 status” or equivalently by “systemctl status apache2”.

It took me a while to find out what was going on and what I had to do. Whilst searching the Internet and experimenting with Apache I passed some interesting information about details of the Apache-installation on Opensuse which may be interesting for others, too.

MPM methods on Apache 2.4

The error message indicated that the whole problem had to do with MPMs – “Multi-Processing-Modules”, i.e. the ability of Apache to handle a multitude of requests concurrently. There are 3 MPM-methods and respective pre-compiled static modules or loadable DSO modules available with Apache 2.4. See e.g.:

digitalocean tutorials how-to-configure-apache-http-with-mpm-event-and-php-fpm-on-ubuntu-18-04-de,
http://httpd.apache.org /docs /current /en /mpm.html
and links therein.

I quote:

  • Pre-fork: A new process is created for each incoming connection reaching the server. Each process is isolated from the others, so no memory is shared between them, even if they are performing identical calls at some point in their execution. This is a safe way to run applications linked to libraries that do not support threading—typically older applications or libraries.
  • Worker: A parent process is responsible for launching a pool of child processes, some of which are listening for new incoming
    connections, and others are serving the requested content. Each process is threaded (a single thread can handle one connection) so one process can handle several requests concurrently. This method of treating connections encourages better resource utilization, while still maintaining stability. This is a result of the pool of available processes, which often has free available threads ready to immediately serve new connections.
  • Event: Based on worker, this MPM goes one step further by optimizing how the parent process schedules tasks to the child processes and the threads associated to those. A connection stays open for 5 seconds by default and closes if no new event happens; this is the keep-alive directive default value, which retains the thread associated to it. The Event MPM enables the process to manage threads so that some threads are free to handle new incoming connections while others are kept bound to the live connections. Allowing re-distribution of assigned tasks to threads will make for better resource utilization and performance.

In a doc at apache.org about performance scaling we furthermore read:

Httpd Configuration
The Apache 2.2 httpd is by default a pre-forking web server. When the server starts, the parent process spawns a number of child processes that do the actual work of servicing requests. But Apache httpd 2.0 introduced the concept of the Multi-Processing Module (MPM). Developers can write MPMs to suit the process- or threading- architecture of their specific operating system. Apache 2 comes with special MPMs for Windows, OS/2, Netware and BeOS. On unix-like platforms, the two most popular MPMs are Prefork and Worker. The Prefork MPM offers the same pre-forking process model that Apache 1.3 uses. The Worker MPM runs a smaller number of child processes, and spawns multiple request handling threads within each child process. In 2.4 MPMs are no longer hard-wired. They too can be exchanged via LoadModule. The default MPM in 2.4 is the event MPM.
….
The maximum number of workers, be they pre-forked child processes or threads within a process, is an indication of how many requests your server can manage concurrently. It is merely a rough estimate because the kernel can queue connection attempts for your web server. When your site becomes busy and the maximum number of workers is running, the machine doesn’t hit a hard limit beyond which clients will be denied access. However, once requests start backing up, system performance is likely to degrade.
Finally, if the httpd server in question is not executing any third-party code, via mod_php, mod_perl or similar, we recommend the use of mpm_event. This MPM is ideal for situations where httpd serves as a thin layer between clients and backend servers doing the real job, such as a proxy or cache.
… 
Selecting your MPM
The prime reason for selecting a threaded MPM is that threads consume fewer system resources than processes, and it takes less effort for the system to switch between threads. This is more true for some operating systems than for others. On systems like Solaris and AIX, manipulating processes is relatively expensive in terms of system resources. On these systems, running a threaded MPM makes sense.
On Linux, the threading implementation actually uses one process for each thread. Linux processes are relatively lightweight, but it means that a threaded MPM offers less of a performance advantage than in other environments.
 
Running a threaded MPM can cause stability problems in some situations For instance, should a child process of a preforked MPM crash, at most one client connection is affected. However, if a threaded child crashes, all the threads in that process disappear, which means all the clients currently being served by that process will see their connection aborted. Additionally, there may be so-called “thread-safety” issues, especially with third-party libraries. In threaded applications, threads may access the same variables indiscriminately, not knowing whether a variable may have been changed by another thread.
 
This has been a sore point within the PHP community. The PHP processor heavily relies on third-party libraries and cannot guarantee that all of these are thread-safe. The good news is that if you are running Apache on Linux, you can run PHP in the preforked MPM without fear of losing too much performance relative to the threaded option.

Ok, what do we learn from this? php_mod is not thread-safe. But regarding performance, using the “pre-fork” MPM method is not really a bad choice on a Linux system. Obviously, this method was used on the workstation. An interesting question, which I come back to later, is whether Opensuse offers dynamically loadable or static MPM modules via its repositories.

Information about the MPM used by your installation?

One (naively) expects that the Apache2 daemon binary should be callable by “/usr/sbin/httpd” on an Opensuse system. Actually, the command “which httpd” gives you “/usr/sbin/httpd” as an answer.

On the Internet you find hints that one can check the compiled and available MPMs by either “httpd -V” and/or “httpd -l“. On the upgraded server MySRV I got: 

MySRV:~ # httpd -V
Server version: Apache/2.4.43 (Linux/SUSE)
Server built:   2020-11-17 11:05:32.000000000 +0000
Server's Module Magic Number: 20120211:92
Server loaded:  APR 1.6.3, APR-UTIL 1.6.1
Compiled using: APR 1.6.3, APR-UTIL 1.6.1
Architecture:   64-bit
Server MPM:     worker
  threaded:     yes (fixed thread count)
    forked:     yes (variable process count)
Server compiled with....
 -D APR_HAS_SENDFILE
 -D APR_HAS_MMAP
....

and

MySRV:~ # httpd -l
Compiled in modules:
  core.c
  mod_so.c
  http_core.c
  worker.c
  mod_unixd.c
  mod_systemd.c

These commands seemingly worked on my server even if the Apache2-service itself could not be started (e.g. by “systemctl start apache2”). The man-pages for “httpd” say that the “-l”-option lists modules which were compiled into the server, i.e. static modules.

What did I get on the workstation? 

MyWS:~ # httpd -V
Server version: Apache/2.4.43 (Linux/SUSE)
Server built:   2021-01-27 09:11:10.000000000 +0000
Server's Module Magic Number: 20120211:92
Server loaded:  APR 1.6.3, APR-UTIL 1.6.1
Compiled using: APR 1.6.3, APR-UTIL 1.6.1
Architecture:   64-bit
Server MPM:     prefork
  threaded:     no
    forked:     yes (variable process count)

and 

MyWS:~ # httpd -l
Compiled in modules:
  core.c
  mod_so.c
  http_core.c
  prefork.c
  mod_unixd.c
  mod_systemd.c

Regarding the actually running processes after Apache-startup on the workstation this result is not too surprising. However, if the listed modules are static then the “httpd” binary on the server must be another one than on the workstation. Why? And how did this come about ?

Another question is: How much can we rely on the information given by e.g. “httpd -l” in the sense that this information reflects facts about the running Apache2 service? We shall see that the answer depends …

Removing the PHP-module on both installations

To analyze further I first aligned the list of modules on both systems via the corresponding setting in “/etc/sysconfig/apache2” to:

APACHE_MODULES=”actions alias auth_basic authn_file authz_host authz_groupfile authz_core authz_user autoindex cgi dir env expires include log_config mime rewrite negotiation
setenvif ssl socache_shmcb userdir reqtimeout php7 authn_core version”

and then removed the “php7” module.

(Instead of editing the file “/etc/sysconfig/apache2” directly you could also use a2enmod or a2dismod, respectively, for changing the module configuration. But I recommend to keep some commented alternatives for in the file for fast changes between repeated tests of different constellations).

In addition I used the seemingly standard Opensuse setting of

APACHE_MPM=””

in “/etc/sysconfig/apache2” for both installations.

Well, as expected no significant changes occurred on the workstation. Apache2 started successfully again (without PHP support); multiple prefork-processes were launched. On the server, however, I now got a successful start, too; “rcapache2 status” showed me a bunch of related processes afterwards: 

MySRV:~ # rcapache2 status
● apache2.service - The Apache Webserver
   Loaded: loaded (/usr/lib/systemd/system/apache2.service; enabled; vendor preset: >
   Active: active (running) since Sun 2021-01-31 11:45:26 CET; 23s ago
  Process: 8555 ExecStop=/usr/sbin/start_apache2 -DSYSTEMD -DFOREGROUND -k graceful->
 Main PID: 20667 (httpd-worker)
   Status: "Processing requests..."
    Tasks: 83
   CGroup: /system.slice/apache2.service
           ├─20667 /usr/sbin/httpd-worker -DSYSCONFIG -DSSL -C PidFile /var/run/httpd.pid ....
           ├─20675 /usr/sbin/httpd-worker -DSYSCONFIG -DSSL -C PidFile /var/run/httpd.pid ....
           ├─20676 /usr/sbin/httpd-worker -DSYSCONFIG -DSSL -C PidFile /var/run/httpd.pid ....
           ├─20677 /usr/sbin/httpd-worker -DSYSCONFIG -DSSL -C PidFile /var/run/httpd.pid ....
           └─20678 /usr/sbin/httpd-worker -DSYSCONFIG -DSSL -C PidFile /var/run/httpd.pid ....

Jan 31 11:45:26 MySRV systemd[1]: Starting The Apache Webserver...
Jan 31 11:45:26 MyServ start_apache2[20667]: AH00548: NameVirtualHost has no effect and>
Jan 31 11:45:26 MySRV systemd[1]: Started The Apache Webserver.

But you see the difference?
=> The programs started were of the type “/usr/bin/http-worker” !

Looking at the startup scripts for the Apache2 service

To dig a bit deeper I looked at the startup scripts used on Opensuse for the Apache2 service. One reason to do so was a comment in Opensuse’s “/etc/sysconfig/apache2” regarding the variable APACHE_MPM: 

# MPM (multi-processing module) to use.
#
# Needed to determine with which MPM apache will run, as well as
# against which header files modules will be built. 
#
# If not set, the system will simply pick one of the installed MPMs.
#
# The implementation of the logic is in /usr/share/apache2/find_mpm,
# a script which can be used standalone as well if needed.

This indicates that some special Opensuse logic is used during startup. But the comment is also misleading: A script “find-mpm” can only be found in the folder “/usr/share/apache2/deprecated-scripts” on a Leap 15.1 and 15.2 systems – and the “script” itself is not used any more, as we shall see in a minute.

So, where do we find the startup-script for Apache? We do not have to look into the systemd configuration for the Apache2 service; the output of the command “rcapache2 status” already revealed it as
“/usr/sbin/start_apache2“.

In it’s script-code we find a line for the execution of a helper script:

 . /usr/share/apache2/script-helpers

and later a call to a function “find_mpm”, followed by some logic for the name of a binary to be saved in the variable “apache_bin”: 

#
# figure out correct apache2 binary (/usr/sbin/httpd-prefork,
# /usr/sbin/httpd-worker, etc.) and serverflags
#
find_mpm
if [ -n "$HTTPD_MPM" ]; then
r
    apache_bin="$HTTPD_SBIN_BASE-$HTTPD_MPM"
    if ! [ -x $apache_bin ]; then
        echo >&2 "$apache_bin-$APACHE_MPM is not a valid httpd binary."
        echo >&2 "Check your APACHE_MPM setting in /etc/sysconfig/apache2."
        exit 1
    fi
else
  echo >&2 "${warn}No Apache binary found. No MPM package installed? $norm"
  echo >&2 "Hint: install the apache2-prefork package, and try again."
  exit 1
fi

Obviously, we will find the function “find_mpm” in “/usr/share/apache2/script-helpers”. A look into this file shows that this really is the case. The outcome of this function influences the startup of Apache2; obviously, a different Apache variant is started for different (valid) values of the script-variable “HTTPD_MPM“: 

apache_bin="$HTTPD_SBIN_BASE-$HTTPD_MPM"

($HTTPD_SBIN_BASE resolves to “/usr/sbin/httpd” – this is set at the beginning of “/usr/share/apache2/script-helpers”.)

Now, you can easily build your own test-script “mpm_test” including this function and print its output:

mpm_test-script:

#!/bin/bash

HTTPD_SBIN_BASE="/usr/sbin/httpd"
#
# loads sysconfig variables into environment
# return value in: APACHE_*
function load_sysconfig
{
  [ -n "$sysconfig_loaded" ] && return
  [ ! -f "$SYSCONFIG_FILE" ] && return

  . $SYSCONFIG_FILE

  export ${!APACHE_*} sysconfig_loaded=true
}
#
# finds prefered multiprocessing module
# return value in: HTTPD_MPM 
function find_mpm
{
  # load sysconfig variables if they weren't yet;
  # this has no effect when find_mpm is not called
  # from start_apache2
  load_sysconfig

  # try to read from sysconfig's APACHE_MPM
  HTTPD_MPM="$APACHE_MPM"
  # if empty, then choose one from installed
  if [ -z "$HTTPD_MPM" ]; then
      installed_mpms=""
      for i in $HTTPD_SBIN_BASE-*; do
          test -f $i || continue
          i=$(basename $i)
          i=${i#*-}
          installed_mpms="$installed_mpms $i"
      done
      # hardcoded preference here:
      for mpm in event worker prefork; do
        if [[ $installed_mpms =~ "$mpm" ]]; then
          HTTPD_MPM=$mpm
          break
        fi
      done
  fi

  # in case no 
  export HTTPD_MPM
}

# ***********************
# Action
# ***********************
find_mpm
echo $HTTPD_MPM

This script produced the following output on my server MySRV (with a running Apache2 without PHP support):

worker

On my workstation (and a running Apache2 with and without PHP support) I got:

prefork

Available and different Apache binaries

Analyzing the logic of our file, which is the same as in the beginning of the startup-script, we see that
“apache_bin” can become either “/usr/sbin/httpd-prefork” or “/usr/sbin/httpd-worker”. It depends on the value of the variable “APACHE_MPM” in “/etc/sysconfig/apache2”:

  • If the variable “APACHE_MPM” is not empty its value is used.
  • But if it is empty the result depends on the existence of one or multiple of the 3 files “httpd-event”, “httpd-worker” or “httpd-prefork” in the folder “/usr/sbin”.

You also see that the logic, which the guys from Opensuse implemented, chooses a MPM-specific variant of Apache2 according to the following fixed priority order:

event > worker > prefork    !

The “prefork” variant has the least priority – and is obviously only chosen if neither the file “httpd-worker” nor the file “httpd-event” exist – and if “APACHE_MPM” is not set otherwise.

A quick check showed that binaries “/usr/sbin/httpd-worker”, “/usr/sbin/httpd-event” did not exist on my workstation MyWS; there, only “/usr/sbin/httpd-prefork” was available. But on the server MySRV I actually had two variants available “/usr/sbin/httpd-prefork” and “/usr/sbin/httpd-worker”.

This fact together with the “find_mpm”-logic explained the different start-up results for Apache2 on my systems MySRV and MyWS !

But not the original cause and why Apache had worked on MySRV with Leap 15.1 before ….

Differences in the package installation?!

The existence of different binaries on MyWS and the server MySRV could only be due to a package difference, which must have been there already before the upgrade to Leap 15.2. A check in my logs and also a look into the package constellation with YaST revealed that on the Leap 15.1 version of the server-system MySRV I actually had installed the RPM “apache2-worker” at some point in time! For some experiments which I had totally forgotten. But not on the workstation. So, I had caused the trouble somehow by myself – without anticipating any consequences for a coming upgrade to Leap 15.2.

But wait a second – this does not explain why I did not run into trouble with Apache on Leap 15.1. Despite the installed package “apache_worker” and an empty “APACHE_MPM” in the sysconfig file….. Why did Apache2 start on Leap 15.1 – as my old log-files show? With “httpd-prefork” processes, by the way …

I had to suspect a difference in the “find_mpm” logic – if I really had left “Apache_MPM” empty on the server. The latter was the case as I saw in my backups. And indeed – on Leap 15.1 the logic of the function “find_mpm” in “/usr/share/apache2/script-helpers” was different:

The old “find_mpm” from Leap 15.1

function find_mpm
{
  [ -n "$mpm_found" ] && return

  # load sysconfig variables if they weren't yet
  load_sysconfig

  # try to read from sysconfig's APACHE_MPM
  HTTPD_MPM=$APACHE_MPM
  # if empty, then choose one from installed
  if [ -z "$HTTPD_MPM" ]; then
      # guess
      for i in $HTTPD_SBIN_BASE-*; do
          test -f $i || continue
          i=$(basename $i)
          i=${i#*-}
          installed_mpms=(${installed_mpms[*]} $i)
      done
      if [ -z "${installed_mpms[*]}" ]; then
          HTTPD_MPM=""
          return
      elif [ ${#installed_mpms[*]} = 1 ]; then
          HTTPD_MPM=${installed_mpms[*]}
      else
          case ${installed_mpms[*]} in
              *prefork*)      HTTPD_MPM=prefork;;
              *worker*)       HTTPD_MPM=worker;;
              *event*)        HTTPD_MPM=event;;
          esac
      fi
  fi

  export HTTPD_MPM mpm_found=true
}

A test shows that the “case”-part of this function gives us an answer “prefork” on a system with both the “prefork” and the “worker” variants of Apache installed!

This makes me wonder why, for heavens sake, the Opensuse guys did not insert a section into their Leap 15.2 Release Notes telling us something about this change!

The solution to my Apache/MPM/PHP problem

After all the information gathering above the very trivial solution to my start-up problem was as that I just had to set the variable “APACHE_MPM” in “/etc/sysconfig/apache2” to

APACHE_MPM=”prefork”

when I wanted a successful start of an Apache instance with PHP support.

What do the http-* files in “/usr/sbin/” look like for multiple MPM-installations?

What happens if we install multiple MPM-variants of Apache? From some parts of the above text you have already concluded that we really must speak of “variants” as the MPM-module is compiled in statically by the Opensuse guys.

On the server MySRV with the worker-MPM active (no PHP loaded) we can see this by using the command ”
apachectl -M”. See the man pages. The result is: 

MySRV: ~# apachectl -M
Loaded Modules:
 core_module (static)
 so_module (static)
 http_module (static)
 mpm_worker_module (static)
 unixd_module (static)
 systemd_module (static)
 actions_module (shared)
 alias_module (shared)
 auth_basic_module (shared)
 authn_file_module (shared)
 authz_host_module (shared)
...
...

So, we expect multiple, relatively big variants of the “http”-binary under “/usr/sbin” whenever we install the packages “apache2-worker” and “apache2-event”. Which I did for fun and step-wise on the workstation MyWS. And indeed – after the installation of the RPM “apache2-worker” we see: 

MyWS:~ # la /usr/sbin/ | grep httpd
lrwxrwxrwx  1 root root           22 Jan 31 16:27 httpd -> /usr/sbin/httpd-worker
-rwxr-xr-x  1 root root       616816 Jan 27 16:17 httpd-prefork
-rwxr-xr-x  1 root root       629200 Jan 27 16:17 httpd-worker
lrwxrwxrwx  1 root root           23 Jan 30 11:02 httpd2 -> /usr/sbin/httpd-prefork
lrwxrwxrwx  1 root root           13 Jan 27 16:17 httpd2-prefork -> httpd-prefork
lrwxrwxrwx  1 root root           12 Jan 27 16:17 httpd2-worker -> httpd-worker

and after an additional installation of the “event” version of Apache2 we get: 

MyWS:~ # la /usr/sbin/ | grep httpd
lrwxrwxrwx  1 root root           21 Jan 31 16:29 httpd -> /usr/sbin/httpd-event
-rwxr-xr-x  1 root root       641552 Jan 27 16:17 httpd-event
-rwxr-xr-x  1 root root       616816 Jan 27 16:17 httpd-prefork
-rwxr-xr-x  1 root root       629200 Jan 27 16:17 httpd-worker
lrwxrwxrwx  1 root root           23 Jan 30 11:02 httpd2 -> /usr/sbin/httpd-prefork
lrwxrwxrwx  1 root root           11 Jan 27 16:17 httpd2-event -> httpd-event
lrwxrwxrwx  1 root root           13 Jan 27 16:17 httpd2-prefork -> httpd-prefork
lrwxrwxrwx  1 root root           12 Jan 27 16:17 httpd2-worker -> httpd-worker

At the end of both installations a post-installation script is running, which creates the binaries, the “httpd”-link and the various “httpd2”-links.

These files/links do not change when we restart Apache2 with a different MPM-setting in “/etc/sysconfig/apache2”.

Can we trust in “httpd -l”? What about “apachectrl -M”?

From the above information we must conclude that we cannot trust the information provided by “httpd -l” or “httpd -V” to give us reliable information for a running Apache2 service on Opensuse. It only shows us, what the most modern MPM among the available ones on the system is. Something similar is to say about “httpd2 -l”; it shows us the other end of the spectrum. Only, if we have just one MPM variant of Apache2 installed all information gets identical and consistent.

If you have a running Apache2 service, a really reliable information regarding the compiled in MPM module is given by “Apachectrl -M” or indirectly by “ps aux | grep httpd”, which reveals the type of the httpd-binary variant started.

Conclusion

Apache2 is provided on Opensuse with static compiled in MPM modules. If you want to choose between different MPMs you have to install related packages; they provide different variants of the httpd-binary which you find afterwards in the directory “/usr/sbin”.

The present Leap 15.2-specific startup-logic for the Apache-service is based an Opensuse-specific script-function “find_mpm” (witin the file “/usr/share/apache2/script-helpers”). According to its logic you MUST specify the MPM-variant via setting a variable in “/etc/sysconfig/apache2” if you want to or must break the fixed preference order “even > worker > prefork”.

Opensuse changed the logic of its MPM selection in the function “find-mpm” between Leap 15.1 and Leap 15.2. This change may, unfortunately, block a successful start of an upgraded Apache2-
service with PHP-support. (A bit of concise information on this point in the Release Notes would have been helpful.)

In case you use “mod_php” for PHP support by Apache2 and thus add “php7” to the list of Apache-modules to be loaded at start-up, you MUST set the “APACHE_MPM”-variable to “prefork” – at least if you follow the standard Opensuse concepts for the Apache service. The enforced choice is reasonable as PHP itself is not thread-safe.

Criticism, Opensuse Apache/PHP deficits and alternatives

As I criticize the handling of Apache2 on Opensuse I also want to add that I miss the flexibility other distributions offer regarding the parallel installation of multiple PHP-versions and a switch between them on the Apache-server. At least with a fast-cgi implementation.

I furthermore do not understand why Opensuse restricts the PHP version in their Update repository to just one and in the PHP-specific repository to the latest 2 versions. And even for these two PHP versions a developer is forced to install two virtual Opensuse machines with different Apache/PHP constellations, if he does not want to change the installed packages all the time.

The somewhat unflexible provision of Apache in combination with PHP and the MPM-logic may make you think about alternatives. There are various situations:

  • If you look beyond Apache I would recommend to setup Nginx.
  • If you look at a way to combine PHP with threaded MPM variants as “worker” or “event, try an installation based on FastCGI and PHP-FPM instead of using php_mod. But consider security aspects then.
  • If you look for support of multiple PHP-versions with Nginx and/or Apache install Debian or Ubuntu in a virtual machine (on a Opensuse host 🙂 ).

For those who like to experiment I have added some links in the last section of this post.

Next post

In the next post I shall cover the startup-problem of the “smartd”-service. This will be a much shorter story.

Links

Links related to the Apache MPM-topic
http://httpd.apache.org /docs /current /en /mpm.html
https://documentation.suse.com/ sles/15-SP2/ html/ SLES-all/cha-apache2.html
http://httpd.apache.org/ docs/ trunk/misc/ perf-scaling.html

Check available MPM-method on Apache
https://www.binarytides.com/check-which-mpm-multi-processing-module-apache-is-running/

Links regarding an alternative FastCGI installation with PHP-FPM
https://en.opensuse.org/ SDB:Apache_FastCGI_and_PHP-FPM_configuration
https://www.p4tchwork.de/apache-php-system-resource-usage/
https://blog.wappler.systems/opensuse-leap-15-apache-2-php-fpm-http2/

Flexible Apache and PHP installations on Debian derivatives
https://www.digitalocean.com/ community/ tutorials/ how-to-configure-apache-http-with-mpm-event-and-php-fpm-on-ubuntu-18-04-de
https://www.epidemiology.tech/apache-php7-4-wordpress-setup/
https://tecadmin.net/setup-apache-php-fpm-ubuntu-20-04/
https://www.interserver.net/ tips/kb/ change-php-version-apache-ubuntu/

Links regarding Nginx
https://techviewleo.com/install-php-on-opensuse-nginx-apache/
https://www.tecmint.com/install-lemp-nginx-php-mariadb-phpmyadmin-in-opensuse/
https://websiteforstudents.com/install-php-7-4-php-7-4-fpm-on-ubuntu-18-04-with-apache2-nginx/

HTTP 2 installation on Opensuse
https://en.opensuse.org/ SDB: Apache_HTTP_2_configuration

Set default target on Opensuse
https://forums.opensuse.org/ showthread.php/ 526792-How-to-change-default-runlevel

Plasma, Nvidia and Wayland
https://community.kde.org/ Plasma/ Wayland/ Nvidia

Upgrade workstation from Opensuse Leap 15.1 to Leap 15.2

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Two weeks ago I upgraded my main Linux-Workstation from Leap 15.1 to Leap 15.2. Some first impressions:

  • Leap 15.2 with KDE/X11 works relatively well. Some minor setting-options for the Plasma desktop have changed.
  • KDE/Wayland with Nvidia cards does not work – unusable for production.
  • No problems with QEMU based KVM- and LXC-container virtualization – my old Debian and Kali guest systems worked as expected on the Leap 15.2-host. No problems with multi-screen configurations of the guests with remote-viewer either.
  • Unexpected high power consumption of the Nvidia card – it has increased by about 5% to 8%. I am not sure whether this is a KDE or a driver problem.
  • The usual suspects for problems during the upgrade are the Nvidia drivers, Pulseaudio, VMware and this time – to my big surprise – CUPS.
  • You may have to change/reset some KDE config and rc-files in your home-directory – especially for the plasma desktop itself.
  • Chromium showed some glitches.

I shortly describe the upgrade process and some obstacles I had to overcome.

Basic upgrade process

I always prepare for a quick restoration of my running system configuration (here: Leap 15.1). Ahead of any upgrade activity, I therefore create a backup of my Leap 15.1 “/”-filesystem on an external drive and in addition create another copy in a target partition on one of my bootable disks. I use the “dd“-command for both purposes. As all productive application and development data as mails, project documents, PHP- and Python modules are on independent partitions or on network locations anyway, the risk of running into major problems afterwards is relatively small. In addition I comment certain critical entries in the “/etc/fstab” out.
In case of a major disaster a recovery can be achieved very quickly by just re-copying the copy of the Leap 15.1 partition back to its original place.

Regarding the backup of the “/”-filesystem to an external disk you have the choice between creating a copy of a partition and creating a (zipped) file. See e.g.:
https://www.poftut.com/linux-dd-command-backup-examples/
https://linoxide.com/linux-command/linux-dd-command-create-1gb-file/
I just made simple partition copies. Regarding the blocksize “bs” option of “dd” I am very generous with SSDs; I use a size like bs=1M or bs=4M to get a reasonable performance. When copying around 100 GB you probably do not want to wait for an hour :-). E.g.:

dd if=/dev/sdg1 of=/dev/sdh5 bs=4M status=progress

Warning 1:

If you copy your partition with “/”-filesystem into another partition, then the target partition must at least have the size of the original one. Really take care of this point! I always try to achieve the exact same size with a partition tool (gparted or YaST partitioner).

Warning 2:

Do not forget to change the UUID of the partition’s copy if the target partition resides on an internal disk; you should never have two filesystems with the same UUID on a system! But write down the original UUID at a safe place. Use “uuidgen
” and the “tune2fs -U” commands to change the copied filesystem’s UUID, afterwards.

See: how-to-change-filesystem-uuid-2-same-uuid

And: In case of an emergency restoration, i.e. after having copied the backup filesystem into its old position, you, of course, have to change the UUID back to the old one.

Why are these UUID-precautions required?
Because of your boot-loader – probably Grub2. Depending on its configuration (and some other system settings) it will probably have created entries in the “/boot/grub2/grub.cfg” which refer to the UUIDs of the bootable partitions. And if such a UUID-reference cannot be resolved in a unique way you may in the best case boot a system you did not want to boot, but you may also experience worse conflicts. Now, you may ask:

What is the copy on the same or another internal hard disk good for anyway?
I create the copy on my main SSD (or another internal disk) not only for restoration purposes, but also for the purpose of transforming it into a fully bootable filesystem at its new position later on – i.e. after the upgrade. I shall return this point in an extra section below.

Upgrade process

After the backup procedures I followed the guideline of the Brasilian Linux Kamarada for the upgrade; see
https://kamarada.github.io/en/2020/09/01/linux-kamarada-and-opensuse-leap-how-to-upgrade-from-151-to-152

Their way of upgrading Opnesuse systems is straight-forward and well-tested. I also liked their recent inclusion of the “releasever“-variable …

I tend to use multiple repositories besides the standard upgrade repository of Opensuse. Therefore, I had to delete quite an amount of repositories following the Kamarada recipe. If you are in the same position, you should make a screenshot of the repository-configuration in YaST to be able to reconfigure them after the upgrade. During the upgrade zypper may recognize many packages for which it has to change the repository. It is a bit of an ordeal to answer to all of the related questions, but I recommend to follow the questions with focused concentration: The order of offered alternatives may change!

Hint: Take care of sufficient filesystem-space! The download of new packages requires extra space during the upgrade period – and usually also the total size of used disk space after an upgrade typically tends to grow somewhat. Therefore: Have at least 20GB available on your “/”-filesystem. (LVM is your friend – if you use(d) it …).

After the upgrade you have to reboot (init 6). If your graphics card is from Nvidia you probably will find yourself on some console terminal and not at a desktop-manager-login (e.g. sddm or gdm3) at the end of the boot process. We must install the (new) Nvidia drivers afterwards.

Nvidia re-setup

There are at least two ways of installing Nvidia-drivers on an Opensuse-system: 1) Directly, i.e. by a manual installation with the help of of the downloaded driver installation scripts. 2) With the help of YaST and the Nvidia community repository. I have used the latter option during the last 2 years. Either way you probably prohibited loading the Opensource Nouveau driver already at some point in the past – e.g. by blacklisting the related kernel module in some of the files in “/etc/modprobe.d”. If not – it is time to do so now.

When you rebooted after the Leap 15.2 upgrade the old Nvidia modules did not work as they were not compiled for the new kernel which was installed during the upgrade. So, from the console login, which you hopefully have reached, you need to invoke YaST in ASCII-mode, activate the
Nvidia community repository and reinstall the proprietary Nvidia drivers from there. In my case the packages

nvidia-computeG05, nvidia-gfxG05-kmp-default, nvidia-glG05, x11-video-nvidiaG05

A compilation is done automatically during this update.
Hint: I also suggest to issue “mkinitrd” immediately after the driver installation to be on the safe side regarding the “initramfs”-phase of the boot-process.
This worked pretty well in may case. After a reboot I got to my SDDM-login screen afterwards. My standard X11-based graphical KDE Plasma desktop started smoothly afterwards. I also tested the functionality of my Cuda installation for Keras and Tensorflow2 – worked perfectly.

Increased idle power consumption of the graphics card on a running KDE plasma desktop (Version 5.18)
A unwelcome surprise regarding Nvidia was the following: When watching the power consumption of my graphics card with

watch -n0.1 nvidia-smi

I saw a rise in the average consumption.
An average value of the GPU load (with “Force Composition Pipeline” activated on all my 3 screens) now had a value of 15%; on my old Leap 15.1 it was below 10%. All with having set the Powermizer mode to “Adaptive” (via (nvidia-settings). I fiddled a bit around with some Nvidia settings – but found no real solution, yet. When I changed a desktop theme (with the help of “systemsettings5”) I observed a drop of power consumption to 11% – but after some movement of windows across my 3 screens it settles again at 15% – quite independent of style and desktop settings. At least with an OpenGL-compositor activated (systemsettings5 >> “screen … >> compositor”. Choosing “Xrender” leads to a drop of GPU-consumption to 9%.

What brought me down a bit to 12% with an activated OpenGL-compositor (OpenGL2 or OpenGL3.1) was to deactivate keeping window-previews:

I did not experience any real disadvantages by doing so. On Leap 15.1 the average consumption with a driver a bit older was still lower by 4% to 5%. We talk about 2 Watt here, but still I do not like such unexpected changes. I do not know whose fault this is – KDE’s or Nvidia’s. We shall see what happens with the next driver version ….

Reconfigure KDE settings

The screen order on my Plasma 5.18 desktop was OK. No screen-tearing (see: Opensuse, KDE Plasma, X11, Nvidia – stop video and screen tearing); my old “xorg.conf“-settings were respected and active.

However, when trying to change design- and plasma-style-settings via “systemsettings5” a click on the “plasma-style”-icon led to a window crash and a Plasma error. This is usually a sign that something is wrong with the KDE configuration files:

Because the KDE setting- and configuration files in the home-directory survive the upgrade untouched some may not be compatible with the new KDE version.

I do not know about an easy way to find out which of the files are to be recreated. My standard way is to make a copy of the “~/.config-directory (with a new suitable name), delete the original directory, wait until it is automatically created again (with new default settings). We
make a copy of this new default-“.config” version (with a unique name), too, and then copy the original version into its standard place again. In the end we have 3 “.config”- directories with different names – one in place with the user’s original settings, one with the new default settings and one with the original settings as “.config”.
Then I overwrite files in the “.config”-file with the new default files, at least those for which I suspect some problems – starting with the plasma-specific “plasma…..rc”-files, then the “systemsettingrc”, then “kwinrc”. Thus, the problems with “plasma-style”-settings could be resolved quickly.

I also got some problems with a standard activation of the OpenGL-compositor at the start of the plasma desktop. A change of the respective settings in the “kwinrc”-file helped – especially “Enabled=True”: 

[Compositing]
AnimationSpeed[$d]
Backend=OpenGL
Enabled=true
GLCore=true
GLPreferBufferSwap=a
GLTextureFilter=1
HiddenPreviews=4
OpenGLIsUnsafe=false
WindowsBlockCompositing=false
XRenderSmoothScale=false

Pulseaudio [PA]

A major frustration came up when I tried to start Clementine and listen to some songs – all my PA-settings were gone with the exception of the PA-LADSPA-equalizer. This had partially to do with changes in the Phonon-settings – now to be found under “systemsettings5 >> Audio“. I had to turn off my onboard HD sound card, activate my mainly used Xonar D2X explicitly and also deactivate an existing XFI-Card, too.

The dialog for setting the KDE/Phonon “standard device” have changed once again :-(. You cannot choose priorities for different sources (audio, video, …) any longer. Simplification? I hate this new KDE politics of taking more and more configuration options away from the standard user. I had to make the equalizer the “standard device” in the new dialog to direct all streams (from browsers and players) through this device.

Compare this to the settings in Leap 15.1; see KDE, Pulseaudio and Browsers – make the LADSPA equalizer the default sink.
In addition: We cannot play test sounds for the various sinks any more. This does no longer work in “YaST Audio” either … I do not call such things progress.

With PA activated “pavucontrol” serves as my primary mixer. It worked more or less as expected though some functionality has been removed there, too. E.g. the ability to remove some input channels completely. Another stupid thing which happens now regarding the default channel for volume adjustment via kmix is now that you may choose “Simultaneous output ….” – but volume controls will affect the Xonar channels, too – at least as long as no device uses the equalizer ….

It took some fiddling until I got back most of my old functionality and sound quality. I found again that its worth to reduce the Clementine input in pavucontrol down to 80% to avoid some oversteering and sound-distortion. Do not forget to set the default channel for sound control with kmix to “Simultaneous output …” for your multi-channel soundcard!

One can in addition install and activate the XFCE-mixer, which basically is a graphical frontend to an alsa mixer. This allows additional shifts of the different channels against each other – performed after pulseaudio’s own mixer settings, namely those of “pavucontrol”.

A major problem with sound and the onboard card:
For some reason a switch from the graphical terminal to a console terminal (by “Ctrl Alt F3”) automatically
activates an Nvidia HDMI stereo device on my system now. It comes up again even if I explicitly deactivated it in the KDE or PA audio settings. I have no solution for this, yet. It affects, however, at least a running Chromium (see below) – and leads to a restart of desktop effects when I return to the graphical session. I get a corresponding explicit message from Plasma ….

VMware – a yearly game of money …

VMware Workstation 15.5 Pro does not work on a Leap 15.2 host without special prerequisites. See e.g.:
https://forums.opensuse.org/showthread.php/540779-vmware-worksation-pro-15-5-not-failed
https://www.opensuse-forum.de/thread/63542-vmware-workstation-pro-leap-15-2b/?pageNo=1
https://communities.vmware.com/t5/VMware-Workstation-Pro/Can-t-compile-wmware-workstation-15-5-on-leap-15-2/m-p/2286237

However, WS Pro 16.0 does. I upgraded to this version. My Win 10 guests felt a bit more sluggish than with WS 15.5. But this may also have to do with a subsequent Upgrade of Win 10 to the 2004 version.

By the way: Note that VMware wants you to pay extra maintenance support, if you order it from SW resellers – at least here in Germany. The cheapest choice was to order it directly from the VMware shop. Do we like such anti-competition monopoly and customer control measures? No, we do not like it => time to get Windows 10 guests running on KVM machines … and to forget VMware for the future. See:
https://getlabsdone.com/10-easy-steps-to-install-windows-10-on-linux-kvm/#Customizing-the-Hardware-for-Windows-10

Hint: Be a bit reluctant with changing the HW compatibility of your VMware virtual machine for two reasons: You may want the virtual image to continue running in your old 15.1 implementation, too – until you feel that Leap 15.2 is stable enough. Second reason: Changing too much of HW settings may lead to a reactivation of your Windows license key.

CUPS bug – reconfigure printers – use the CUPS packages from the printing repository

I have two printers in my network. They can be addressed both by a local configuration and via a cups server in the net, which offers a variety of queues.
The reconfiguration of the local settings were a piece of cake with YaST. The updated HP-drivers simply worked.
However, printing from my system via a CUPS server in the net and its queues did not work any more. In contrast to all previous upgrades of at least the last 4 years :-(.
It took me a while to find out that this is due to a major bug in the present CUPS version delivered by the standard Update repository of Opensuse. Use the CUPS version > 2.3.0 from the “Printing repository“.
Then your server based queues will work again!

Chromium: Problems with HW acceleration / sound from Chromium does not get upmixed on a multichannel sound card

I had some problems with Chromium. Maybe I had them already before, but I noticed them now:
I had to refrain from HW-acceleration: Whenever I changed to one of the console terminals (e.g. Ctrl-Alt-F2) and returned to the graphical terminal the Chromium user interface got totally destroyed. Not funny when you were editing a blog :-(.
In addition: Chromium sound does not get upmixed completely – the probable reason is that Chromium supports real 7.1 channel sound these days. So, stereo may remain stereo or only gets upmixed by some special soundcard setting to 4.0, 6.0 – but not by PA. Despite such
settings on my Xonar card, I had some disturbing experiences: When changing to a console terminal and back to the graphical one, the upmixing changed from 4.0 to 2.0 …. :-(. When I rebooted afterwards, the 4.0 upmixing was there again. The whole effect probably was due to an automatic activation of some onboard/oncard Nvidia HDMI sound channels during the switch to the console terminals.

Firefox sound, however, which sends a pure stereo signal to the system as, gets properly upmixed by PA to 7.1 sound and this remains stable during switches between console and graphical terminals. So, for the time being, I do not use chromium for TV streaming any longer. Maybe the Chromium developers should have a talk with the PA developer …. It seems to be a difficult problem to me – you would have to analyze that only stereo sound is coming despite a 8 channel signal. A simple workaround would be that we get a switch in the chromium browser which allows to set its operation from multichannel to stereo, only.

For those who like to experiment with “pactl” commands (like “pactl list sinks” as standard user) I would like to draw your attention to work others ave done regarding PA and upmixing:
https://gist.github.com/dex4er/8646669
https://bbs.archlinux.de/viewtopic.php?id=16093

It should be possible to write two scripts one activating a certain upmixing with pactl commands and one deactivating it again. But my time is so limited that I haven’t tried it myself, yet.

KDE Plasma, Nvidia and Wayland do not work

As with Leap 15.1, KDE and Wayland lead to a direct crash on my workstation with Nividia graphics. The system freezes. You have to enforce a reset of your PC and start a reboot. However, on a laptop with a i915 Intel driver for a CPU integrated graphics Wayland works. So, we have a clear Nvidia topic here.

After the upgrade: Make the copy of our original partition of Leap 15.1 a bootable one

If you had copied your original Leap 15.1 partition into another partition on your hard disk you may want to make it a bootable fully functional system offered as an entry in the Grub2 menu. This requires some additional efforts.

Firstly, you have to change all references to the modified UUID in the internal boot-relevant files of the moved filesystem – i.e. in the “/etc/fstab”  AND  in the “/boot/grub2/grub.cfg” there on the Leap 15.1-partition. For this purpose you must mount the copied Leap 15.1 partition on your running Leap 15.2 system and edit the entries in both files of the mounted Leap 15.1 filesystem very carefully with respect to the changed UUID (see the sections on backups above). Take care that you do not change the files on the running Leap 15.2 system. And, please, make copies of both files before you change them! You may need the original contents.

Instead ofchnaging entries in the “/boot/grub2/grub.cfg” of the Leap 15.1 copy you can also rename the “/boot/grub2/grub.conf” on the Leap 15.1 partition to something like “grub.conf_orig” (you want to keep the contents!). This gives the grub “os-prober” on you Leap 15.2 installation a chance to create correct entries regarding the address of the partition.

Then we remove the “/boot/grub2/grub.cfg” in the Leap 15.2 installation and run “grub2-mkconfig -o /boot/grub2/grub.cfg” again to give the os-prober there a chance to create valid entries. Please, cou check these entries first before you install the grub loader from your running Leap 15.2 again! If you find correct UUID or other references to the partition the you can reinstall the bootloader. I always do this with YaST. Afterwards you should be able to boot both your new Leap 15.2 and your old 15.1 installation a respective entries in the Grub2 menu. Thus we have our old Leap 15.1
installation available for comparisons.

Conclusion

An upgrade of a Linux workstation from Opensuse Leap 15.1 to Leap 15.2 brought no major problems with it. One remarkable exception is a bug in the CUPS package – for which you find a solution in form of a newer package in another Suse repository. The fact that Wayland does not work with KDE on Nvidia graphics came not unexpected – although I think its a shame for Nvidia. The same could be said about the increased power consumption of the Nvidia card.

Have fun with Leap 15.2.