Fedora 31 Self-Contained Change proposal: DNF Make Best Mode the Default

[Ben Cotton]

https://fedoraproject.org/wiki/Changes/DNF_Default_Best

== Summary ==
Currently, DNF prefers clean dependency resolution over package updates;
a package (almost) silently won't get updated to a newer version if the new
version has dependency problems. DNF will be changed to prefer updates and fail
if they have dependency resolution issues, while the failure has a
temporal or permanent workaround
hint for users who want to use the older behavior.

== Owner ==
* Name: [[User:jmracek| Jaroslav Mracek]]
* Email: jmracek(a)redhat.com


== Detailed Description ==
Change the built-in default value of the `best` configuration option
from `0` (false) to `1` (true).

As a result, unless `best` is overridden in the `/etc/dnf/dnf.conf`
file or using `--setopt`, it will default to `1`. As a convenience, we
will also put the explicit `best=1` assignment in the shipped
`/etc/dnf/dnf.conf` file for better transparency, and introduce the
new `--nobest` command-line switch.

The purpose of the `--nobest` switch (as a shorthand for
`--setopt=best=0`) is to make it easy for the user to override the
default setting when needed, and it will also be
[https://github.com/rpm-software-management/dnf/pull/1311/commits/9a3e8fd0...
suggested] in the DNF output when a dependency error occurs.

Relevant excerpt from the updated `dnf.conf(5)`:
<pre>
best  boolean
When upgrading a package, always try to install its highest version
available, even only to find out some of its deps are not satisfiable.
Enable this if you want to experience broken dependencies in the
repositories firsthand. The default is True.
</pre>

Relevant excerpt from the updated `dnf(8)`:
<pre>
--nobest
Set best option as false, therefore transactions are not limited to
only best candidates.
</pre>

'''Change in DNF output - missing
vim-enhanced-2:8.1.1561-1.fc30'''

Original output. DNF succeed with return code 0:
<pre>
sudo dnf upgrade
Last metadata expiration check: 2:16:40 ago on Mon 24 Jun 2019 04:27:16 PM CEST.
Dependencies resolved.

 Problem: package vim-enhanced-2:8.1.1471-1.fc30.x86_64 requires
vim-common = 2:8.1.1471-1.fc30, but none of the providers can be
installed
  - cannot install both vim-common-2:8.1.1561-1.fc30.x86_64 and
vim-common-2:8.1.1471-1.fc30.x86_64
  - problem with installed package vim-enhanced-2:8.1.1471-1.fc30.x86_64
  - cannot install the best update candidate for package
vim-common-2:8.1.1471-1.fc30.x86_64
  - package vim-enhanced-2:8.1.1561-1.fc30.x86_64 is excluded
===================================================================================================================================
 Package                        Architecture               Version
                           Repository                   Size
===================================================================================================================================
Skipping packages with conflicts:
(add '--best --allowerasing' to command line to force their upgrade):
 vim-common                     x86_64
2:8.1.1561-1.fc30                      updates                     6.7
M

Transaction Summary
===================================================================================================================================
Skip  1 Package

Nothing to do.
Complete!
</pre>

Output after the change. DNF fails with return code 1, but proposing
`--nobest` option as an option to resolve the issue:
<pre>
sudo dnf upgrade
Last metadata expiration check: 2:16:36 ago on Mon 24 Jun 2019 04:27:16 PM CEST.
Error:
 Problem: package vim-enhanced-2:8.1.1471-1.fc30.x86_64 requires
vim-common = 2:8.1.1471-1.fc30, but none of the providers can be
installed
  - cannot install both vim-common-2:8.1.1561-1.fc30.x86_64 and
vim-common-2:8.1.1471-1.fc30.x86_64
  - problem with installed package vim-enhanced-2:8.1.1471-1.fc30.x86_64
  - cannot install the best update candidate for package
vim-common-2:8.1.1471-1.fc30.x86_64
  - package vim-enhanced-2:8.1.1561-1.fc30.x86_64 is excluded
(try to add '--allowerasing' to command line to replace conflicting
packages or '--skip-broken' to skip uninstallable packages or
'--nobest' to use not only best candidate packages)
</pre>

'''Q&A'''

Can be a default of the best configuration option overwritten easily
and permanently by user?
Yes, just add `best=false` to `/etc/dnf/dnf.conf`
<pre>
[main]
best=False
</pre>

Can be a default of the best configuration option overwritten easily
from commandline?
Yes, just add `--nobest` to command
<pre>
dnf upgrade --nobest
</pre>

What about PackageKit and Gnome Software?
<pre>
PackageKit and Gnome Software will be not affected by the change. In
case that the same behavior will be desired for PackageKit, It will
require changes in PackageKit code.
</pre>

What about Microdnf?
<pre>
Microdnf will be not affected by the change. There is a plan to unify
functional parity and behavior DNF with Microdnf but not before Fedora
33.
</pre>


== Benefit to Fedora ==

This change allows the users to be properly notified when a package
cannot be upgraded to the latest version, instead of silently ignoring
it as an upgrade candidate.

Right now, when DNF runs in `best=0` mode, if a package cannot be
upgraded due to dependency problems, it is skipped and a warning is
printed in the transaction summary table. However, this poses a risk
of important security fixes being overlooked by the user in case they
are broken for some reason, such as due to a repository
misconfiguration or inconsistency within the metadata itself.

Moreover, since DNF always exits with the return code `0` (success)
when in `best=0` mode, this mode is especially risky in automated
scripts invoking DNF in `assumeyes` mode in which case such
unsuccessful package upgrades could easily go unnoticed unless the
logs are manually examined after the fact.

The new behavior is also more in line with the generally accepted
software development practice of failing early and failing fast.

As a secondary benefit, broken upgrade paths in the Fedora
repositories will hopefully be noticed, reported and therefore fixed
sooner. Although, we would prefer if such problems would be detected
before we ship them to users.

'''Summary of benefits:'''

# No silently passed problems with updates
# Broken dependencies faster disappear from Fedora distribution
# Problems will be reported more often - opportunity to fix issues
# Increase in stability of Fedora distribution
# Less issues after branching
# Identical behavior of DNF in all distributions - Fedora/RHEL/Mageia/OpenSuse

== Scope ==
* Proposal owners:
The change is already part of the upstream (dnf-4.1.0) and reverted in
Fedora downstream. The change was composed by following pull requests:

https://github.com/rpm-software-management/libdnf/pull/678<br>
https://github.com/rpm-software-management/dnf/pull/1311<br>
https://github.com/rpm-software-management/dnf/pull/1316<br>
https://github.com/rpm-software-management/dnf/pull/1319

We would like to stop the reverting the changes.

* Other developers: N/A (not a System Wide Change)
* Policies and guidelines: N/A (not a System Wide Change)
* Trademark approval: N/A (not needed for this Change)

== Upgrade/compatibility impact ==
N/A (not a System Wide Change)

== How To Test ==
N/A (not a System Wide Change)

== User Experience ==
Broken upgrades are recognized early, enabling the users to act upon
them by double-checking their repository configuration or filing bugs,
instead of assuming no upgrades are available.

== Dependencies ==
N/A (not a System Wide Change)

== Contingency Plan ==
If there is a massive negative feedback by the rawhide and pre-beta
users, we can revert the
change at the beta freeze. If there is a massive negative feedback by
the beta users, we can
revert the change at final freeze.

* Contingency mechanism: (What to do?  Who will do it?) N/A (not a
System Wide Change)
* Contingency deadline: N/A (not a System Wide Change)
* Blocks release? N/A (not a System Wide Change), Yes/No

== Documentation ==
N/A (not a System Wide Change)

== Release Notes ==

-- 
Ben Cotton
He / Him / His
Fedora Program Manager
Red Hat
TZ=America/Indiana/Indianapolis

[Björn Persson]

If I understand this change correctly, then:

· Before: If one package update is uninstallable, then that package
won't be updated, but other packages can still be updated.

· After: If one package update is uninstallable, then *nothing* will be
updated.

And you call that an improvement?

> Relevant excerpt from the updated `dnf.conf(5)`:
> <pre>
> best  boolean
> When upgrading a package, always try to install its highest version
> available, even only to find out some of its deps are not satisfiable.
> Enable this if you want to experience broken dependencies in the
> repositories firsthand. The default is True.
> </pre> 
"Best" is an absolutely terrible name for this option. By what
definition is an unusable package "better" than a lower-numbered
package that can actually be installed?

> Right now, when DNF runs in `best=0` mode, if a package cannot be
> upgraded due to dependency problems, it is skipped and a warning is
> printed in the transaction summary table. However, this poses a risk
> of important security fixes being overlooked by the user in case they
> are broken for some reason, such as due to a repository
> misconfiguration or inconsistency within the metadata itself. 
If there is a significant risk that the warning will be overlooked,
then how about just making the warning more visible?

> Moreover, since DNF always exits with the return code `0` (success)
> when in `best=0` mode, this mode is especially risky in automated
> scripts 
Would it not be possible to program DNF to update what can be updated
and then return a nonzero exit code?

Björn Persson

[Dan Book]

On Thu, Jun 27, 2019 at 12:30 PM Björn Persson <Bjorn(a)xn--rombobjrn-67a.se&gt; wrote:

>  If there is a significant risk that the warning will be overlooked,
>  then how about just making the warning more visible?
>
>  
Based on experience with people installing things from CPAN for Perl, there
is no "more visible" that has any appreciable impact unless it causes the
process to fail.

-Dan

[Florian Weimer]

* Björn Persson:

>  If I understand this change correctly, then:
>
>  · Before: If one package update is uninstallable, then that package
>  won't be updated, but other packages can still be updated.
>
>  · After: If one package update is uninstallable, then *nothing* will be
>  updated.
>
>  And you call that an improvement? 
It is.  People have missed glibc updates because of the broken composes
without realizing it for quite some time, for example.

Thanks,
Florian

[Neal Gompa]

On Thu, Jun 27, 2019 at 11:25 AM Ben Cotton <bcotton(a)redhat.com&gt; wrote:
>  https://fedoraproject.org/wiki/Changes/DNF_Default_Best
>
>  == Summary ==
>  Currently, DNF prefers clean dependency resolution over package updates;
>  a package (almost) silently won't get updated to a newer version if the new
>  version has dependency problems. DNF will be changed to prefer updates and fail
>  if they have dependency resolution issues, while the failure has a
>  temporal or permanent workaround
>  hint for users who want to use the older behavior.
>
>  == Owner ==
>  * Name: [[User:jmracek| Jaroslav Mracek]]
>  * Email: jmracek(a)redhat.com
>
>
>  == Detailed Description ==
>  Change the built-in default value of the `best` configuration option
>  from `0` (false) to `1` (true).
>
>  As a result, unless `best` is overridden in the `/etc/dnf/dnf.conf`
>  file or using `--setopt`, it will default to `1`. As a convenience, we
>  will also put the explicit `best=1` assignment in the shipped
>  `/etc/dnf/dnf.conf` file for better transparency, and introduce the
>  new `--nobest` command-line switch.
>
>  The purpose of the `--nobest` switch (as a shorthand for
>  `--setopt=best=0`) is to make it easy for the user to override the
>  default setting when needed, and it will also be
>
> [https://github.com/rpm-software-management/dnf/pull/1311/commits/9a3e8fd0...
>  suggested] in the DNF output when a dependency error occurs.
>
>  Relevant excerpt from the updated `dnf.conf(5)`:
>  <pre>
>  best  boolean
>  When upgrading a package, always try to install its highest version
>  available, even only to find out some of its deps are not satisfiable.
>  Enable this if you want to experience broken dependencies in the
>  repositories firsthand. The default is True.
>  </pre>
>
>  Relevant excerpt from the updated `dnf(8)`:
>  <pre>
>  --nobest
>  Set best option as false, therefore transactions are not limited to
>  only best candidates.
>  </pre>
>
>  '''Change in DNF output - missing
> vim-enhanced-2:8.1.1561-1.fc30'''
>
>  Original output. DNF succeed with return code 0:
>  <pre>
>  sudo dnf upgrade
>  Last metadata expiration check: 2:16:40 ago on Mon 24 Jun 2019 04:27:16 PM CEST.
>  Dependencies resolved.
>
>   Problem: package vim-enhanced-2:8.1.1471-1.fc30.x86_64 requires
>  vim-common = 2:8.1.1471-1.fc30, but none of the providers can be
>  installed
>    - cannot install both vim-common-2:8.1.1561-1.fc30.x86_64 and
>  vim-common-2:8.1.1471-1.fc30.x86_64
>    - problem with installed package vim-enhanced-2:8.1.1471-1.fc30.x86_64
>    - cannot install the best update candidate for package
>  vim-common-2:8.1.1471-1.fc30.x86_64
>    - package vim-enhanced-2:8.1.1561-1.fc30.x86_64 is excluded
>
> ===================================================================================================================================
>   Package                        Architecture               Version
>                             Repository                   Size
>
> ===================================================================================================================================
>  Skipping packages with conflicts:
>  (add '--best --allowerasing' to command line to force their upgrade):
>   vim-common                     x86_64
>  2:8.1.1561-1.fc30                      updates                     6.7
>  M
>
>  Transaction Summary
>
> ===================================================================================================================================
>  Skip  1 Package
>
>  Nothing to do.
>  Complete!
>  </pre>
>
>  Output after the change. DNF fails with return code 1, but proposing
>  `--nobest` option as an option to resolve the issue:
>  <pre>
>  sudo dnf upgrade
>  Last metadata expiration check: 2:16:36 ago on Mon 24 Jun 2019 04:27:16 PM CEST.
>  Error:
>   Problem: package vim-enhanced-2:8.1.1471-1.fc30.x86_64 requires
>  vim-common = 2:8.1.1471-1.fc30, but none of the providers can be
>  installed
>    - cannot install both vim-common-2:8.1.1561-1.fc30.x86_64 and
>  vim-common-2:8.1.1471-1.fc30.x86_64
>    - problem with installed package vim-enhanced-2:8.1.1471-1.fc30.x86_64
>    - cannot install the best update candidate for package
>  vim-common-2:8.1.1471-1.fc30.x86_64
>    - package vim-enhanced-2:8.1.1561-1.fc30.x86_64 is excluded
>  (try to add '--allowerasing' to command line to replace conflicting
>  packages or '--skip-broken' to skip uninstallable packages or
>  '--nobest' to use not only best candidate packages)
>  </pre>
>
>  '''Q&A'''
>
>  Can be a default of the best configuration option overwritten easily
>  and permanently by user?
>  Yes, just add `best=false` to `/etc/dnf/dnf.conf`
>  <pre>
>  [main]
>  best=False
>  </pre>
>
>  Can be a default of the best configuration option overwritten easily
>  from commandline?
>  Yes, just add `--nobest` to command
>  <pre>
>  dnf upgrade --nobest
>  </pre>
>
>  What about PackageKit and Gnome Software?
>  <pre>
>  PackageKit and Gnome Software will be not affected by the change. In
>  case that the same behavior will be desired for PackageKit, It will
>  require changes in PackageKit code.
>  </pre>
>
>  What about Microdnf?
>  <pre>
>  Microdnf will be not affected by the change. There is a plan to unify
>  functional parity and behavior DNF with Microdnf but not before Fedora
>  33.
>  </pre>
>
>
>  == Benefit to Fedora ==
>
>  This change allows the users to be properly notified when a package
>  cannot be upgraded to the latest version, instead of silently ignoring
>  it as an upgrade candidate.
>
>  Right now, when DNF runs in `best=0` mode, if a package cannot be
>  upgraded due to dependency problems, it is skipped and a warning is
>  printed in the transaction summary table. However, this poses a risk
>  of important security fixes being overlooked by the user in case they
>  are broken for some reason, such as due to a repository
>  misconfiguration or inconsistency within the metadata itself.
>
>  Moreover, since DNF always exits with the return code `0` (success)
>  when in `best=0` mode, this mode is especially risky in automated
>  scripts invoking DNF in `assumeyes` mode in which case such
>  unsuccessful package upgrades could easily go unnoticed unless the
>  logs are manually examined after the fact.
>
>  The new behavior is also more in line with the generally accepted
>  software development practice of failing early and failing fast.
>
>  As a secondary benefit, broken upgrade paths in the Fedora
>  repositories will hopefully be noticed, reported and therefore fixed
>  sooner. Although, we would prefer if such problems would be detected
>  before we ship them to users.
>
>  '''Summary of benefits:'''
>
>  # No silently passed problems with updates
>  # Broken dependencies faster disappear from Fedora distribution
>  # Problems will be reported more often - opportunity to fix issues
>  # Increase in stability of Fedora distribution
>  # Less issues after branching
>  # Identical behavior of DNF in all distributions - Fedora/RHEL/Mageia/OpenSuse
>
>  == Scope ==
>  * Proposal owners:
>  The change is already part of the upstream (dnf-4.1.0) and reverted in
>  Fedora downstream. The change was composed by following pull requests:
>
>  https://github.com/rpm-software-management/libdnf/pull/678<br>
>  https://github.com/rpm-software-management/dnf/pull/1311<br>
>  https://github.com/rpm-software-management/dnf/pull/1316<br>
>  https://github.com/rpm-software-management/dnf/pull/1319
>
>  We would like to stop the reverting the changes.
>
>  * Other developers: N/A (not a System Wide Change)
>  * Policies and guidelines: N/A (not a System Wide Change)
>  * Trademark approval: N/A (not needed for this Change)
>
>  == Upgrade/compatibility impact ==
>  N/A (not a System Wide Change)
>
>  == How To Test ==
>  N/A (not a System Wide Change)
>
>  == User Experience ==
>  Broken upgrades are recognized early, enabling the users to act upon
>  them by double-checking their repository configuration or filing bugs,
>  instead of assuming no upgrades are available.
>  
So, while it *is* true that Mageia, OpenMandriva, and openSUSE are
shipping with this feature for DNF, the experience isn't what I
consider optimal. I would like to see user experience improvements as
part of making this change. Specifically, when such a dependency error
occurs, I would like to see it prompt the user on what to do, rather
than forcing them to re-run the whole thing over again with a switch
like `--no-best` (which is a terrible name...) or `--allowerasing`.

Zypper offers this capability, so I know libsolv provides a way to do
it. There's no reason DNF can't do that too.

Moreover, this change impacts all consumers of the DNF Python API,
including dnfdragora (through dnfdaemon). The behavior change needs to
be validated with that tool as well, and there's no way to run a
transaction with another flag from that program, so adjustments are
likely necessary there.




--
真実はいつも一つ！/ Always, there's only one truth!

[Zbigniew Jędrzejewski-Szmek]

On Thu, Jun 27, 2019 at 10:37:28AM -0400, Ben Cotton wrote:
>  https://fedoraproject.org/wiki/Changes/DNF_Default_Best 
I wanted to update today, and I got the following report:
$ sudo dnf upgrade --best
Last metadata expiration check: 0:00:18 ago on Thu 27 Jun 2019 10:45:00 PM CEST.
Error: 
 Problem: package InsightToolkit-4.9.1-9.fc29.x86_64 requires libnetlib.so.1.14()(64bit),
but none of the providers can be installed
  - package InsightToolkit-4.9.1-9.fc29.x86_64 requires libv3p_netlib.so.1.14()(64bit),
but none of the providers can be installed
  - package InsightToolkit-4.9.1-9.fc29.x86_64 requires libvcl.so.1.14()(64bit), but none
of the providers can be installed
  - package InsightToolkit-4.9.1-9.fc29.x86_64 requires libvnl.so.1.14()(64bit), but none
of the providers can be installed
  - package InsightToolkit-4.9.1-9.fc29.x86_64 requires libvnl_algo.so.1.14()(64bit), but
none of the providers can be installed
  - cannot install both vxl-2.0.2-4.fc30.x86_64 and vxl-1.17.0-30.fc30.x86_64
  - cannot install both vxl-1.17.0-30.fc30.x86_64 and vxl-2.0.2-4.fc30.x86_64
  - cannot install the best update candidate for package vxl-1.17.0-30.fc30.x86_64
  - cannot install the best update candidate for package
InsightToolkit-4.9.1-9.fc29.x86_64
(try to add '--allowerasing' to command line to replace conflicting packages or
'--skip-broken' to skip uninstallable packages)

The problem with this is that it's not possible to figure out what who is too blame.
Specifically:
1. How am I to know that vxl is related to libnetlib.so.1.14()(64bit) and
   the other virtual provides?

2.
>  - cannot install the best update candidate for package
> vxl-1.17.0-30.fc30.x86_64
>  - cannot install the best update candidate for package InsightToolkit-4.9.1-9.fc29.x86_64
I see that vxl-1.17 and vxl-2.0.2 are mentioned. 1.17 is the older version.
So this message talks about old vxl version, so I assume it also talks about
old InsightToolkit version. But all logs above that only talk about one version
of InsightToolkit. Why would I care about requirements of the old version, when
about to upgrade to new version? What is even the new InsightToolkit version
dnf is trying to upgrade to?

3.
>   - cannot install both vxl-2.0.2-4.fc30.x86_64 and
> vxl-1.17.0-30.fc30.x86_64
>   - cannot install both vxl-1.17.0-30.fc30.x86_64 and vxl-2.0.2-4.fc30.x86_64 
The
second line is noise, already reported previously, but I can't find the bug
now.

So even in simple case with two packages, I'd need to do repoquery spelunking
to figure out what is going on. If dnf could tell me something like...

 Problem: package InsightToolkit-4.9.1-9.fc29.x86_64 requires
  libnetlib.so.1.14()(64bit), libv3p_netlib.so.1.14()(64bit),
  libvcl.so.1.14()(64bit), libvnl.so.1.14()(64bit),
  libvnl_algo.so.1.14()(64bit), currently provided by vxl-1.17.0.
  - There is no upgrade candidate for InsightToolkit.
  - Best upgrade candidate vxl-2.0.2-4.fc30.x86_64 does have those Provides.
    → cannot install both vxl-2.0.2-4.fc30.x86_64 and vxl-1.17.0-30.fc30.x86_64 because
vxl is not an installonly package.
       → cannot install the best update candidate for package vxl

i.e. group relevant Provides that "connect" two package into one list instead
of repeating the whole set of messages every time,
don't talk about upgrade candidates that don't actually exist,
mention the connection between Provides and package names,
omit evra when not required,
provide more explanations in general,

then I'd see this change in a more positive light. I think the output
right now is just noise for most users.

The premise that bug reports from users will help us catch such cases
— I don't see this as true. We *already know* that InsightToolkit has a problem,
there's a FTBFS bug for it somewhere.

The idea of "fault tolerant systems" is that the system mostly
continues to work in face of small failures in components. The distro
is a big system with thousands of interacting components, and *some*
simply must fail occasionally. The proposal is to make the system
fault-intolerant to notice errors earlier. That just seems wrong.
Returning to the example, why can't dnf print in red letters
at the end of the transaction log:

  Upgrade of vxl-1.17.0-30.fc30.x86_64 to vxl-2.0.2-4.fc30.x86_64 was held back because of
dependency issues.

Users would see that too.

Zbyszek

[Vít Ondruch]

Dne 27. 06. 19 v 23:56 Zbigniew Jędrzejewski-Szmek napsal(a):
>  On Thu, Jun 27, 2019 at 10:37:28AM -0400, Ben Cotton wrote:
> > https://fedoraproject.org/wiki/Changes/DNF_Default_Best
>  I wanted to update today, and I got the following report:
>  $ sudo dnf upgrade --best
>  Last metadata expiration check: 0:00:18 ago on Thu 27 Jun 2019 10:45:00 PM CEST.
>  Error: 
>   Problem: package InsightToolkit-4.9.1-9.fc29.x86_64 requires libnetlib.so.1.14()(64bit),
> but none of the providers can be installed
>    - package InsightToolkit-4.9.1-9.fc29.x86_64 requires libv3p_netlib.so.1.14()(64bit),
> but none of the providers can be installed
>    - package InsightToolkit-4.9.1-9.fc29.x86_64 requires libvcl.so.1.14()(64bit), but none
> of the providers can be installed
>    - package InsightToolkit-4.9.1-9.fc29.x86_64 requires libvnl.so.1.14()(64bit), but none
> of the providers can be installed
>    - package InsightToolkit-4.9.1-9.fc29.x86_64 requires libvnl_algo.so.1.14()(64bit), but
> none of the providers can be installed
>    - cannot install both vxl-2.0.2-4.fc30.x86_64 and vxl-1.17.0-30.fc30.x86_64
>    - cannot install both vxl-1.17.0-30.fc30.x86_64 and vxl-2.0.2-4.fc30.x86_64
>    - cannot install the best update candidate for package vxl-1.17.0-30.fc30.x86_64
>    - cannot install the best update candidate for package
> InsightToolkit-4.9.1-9.fc29.x86_64
>  (try to add '--allowerasing' to command line to replace conflicting packages or
> '--skip-broken' to skip uninstallable packages)
>
>  The problem with this is that it's not possible to figure out what who is too blame.
>  Specifically:
>  1. How am I to know that vxl is related to libnetlib.so.1.14()(64bit) and
>     the other virtual provides?
>
>  2.
> > - cannot install the best update candidate for package vxl-1.17.0-30.fc30.x86_64
> > - cannot install the best update candidate for package
> InsightToolkit-4.9.1-9.fc29.x86_64
>  I see that vxl-1.17 and vxl-2.0.2 are mentioned. 1.17 is the older version.
>  So this message talks about old vxl version, so I assume it also talks about
>  old InsightToolkit version. But all logs above that only talk about one version
>  of InsightToolkit. Why would I care about requirements of the old version, when
>  about to upgrade to new version? What is even the new InsightToolkit version
>  dnf is trying to upgrade to?
>
>  3.
> >  - cannot install both vxl-2.0.2-4.fc30.x86_64 and vxl-1.17.0-30.fc30.x86_64
> >  - cannot install both vxl-1.17.0-30.fc30.x86_64 and vxl-2.0.2-4.fc30.x86_64
>  The second line is noise, already reported previously, but I can't find the bug
>  now.
>
>  So even in simple case with two packages, I'd need to do repoquery spelunking
>  to figure out what is going on. If dnf could tell me something like...
>
>   Problem: package InsightToolkit-4.9.1-9.fc29.x86_64 requires
>    libnetlib.so.1.14()(64bit), libv3p_netlib.so.1.14()(64bit),
>    libvcl.so.1.14()(64bit), libvnl.so.1.14()(64bit),
>    libvnl_algo.so.1.14()(64bit), currently provided by vxl-1.17.0.
>    - There is no upgrade candidate for InsightToolkit.
>    - Best upgrade candidate vxl-2.0.2-4.fc30.x86_64 does have those Provides.
>      → cannot install both vxl-2.0.2-4.fc30.x86_64 and vxl-1.17.0-30.fc30.x86_64 because
> vxl is not an installonly package.
>         → cannot install the best update candidate for package vxl
>
>  i.e. group relevant Provides that "connect" two package into one list instead
>  of repeating the whole set of messages every time,
>  don't talk about upgrade candidates that don't actually exist,
>  mention the connection between Provides and package names,
>  omit evra when not required,
>  provide more explanations in general,
>
>  then I'd see this change in a more positive light. I think the output
>  right now is just noise for most users.
>
>  The premise that bug reports from users will help us catch such cases
>  — I don't see this as true. We *already know* that InsightToolkit has a problem,
>  there's a FTBFS bug for it somewhere.
>
>  The idea of "fault tolerant systems" is that the system mostly
>  continues to work in face of small failures in components. The distro
>  is a big system with thousands of interacting components, and *some*
>  simply must fail occasionally. The proposal is to make the system
>  fault-intolerant to notice errors earlier. That just seems wrong.
>  Returning to the example, why can't dnf print in red letters
>  at the end of the transaction log:
>
>    Upgrade of vxl-1.17.0-30.fc30.x86_64 to vxl-2.0.2-4.fc30.x86_64 was held back because
> of dependency issues.
>
>  Users would see that too. 

Yep, this is problem. I opened DNF tickets requesting improvement of the
messages, but apparently unsuccessfully :(


Vít


>
> Zbyszek
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[Miroslav Suchý]

Dne 27. 06. 19 v 23:56 Zbigniew Jędrzejewski-Szmek napsal(a):
>  (try to add '--allowerasing' to command line to replace
> conflicting packages or '--skip-broken' to skip uninstallable packages) 
This is message for people who are willing/are able to fix or report things. For regular
user this should be
  .. or run with "--nobest" to skip broken deps.

-- 
Miroslav Suchy, RHCA
Red Hat, Associate Manager ABRT/Copr, #brno, #fedora-buildsys

[Kamil Paral]

On Fri, Jun 28, 2019 at 11:12 AM Miroslav Suchý <msuchy(a)redhat.com&gt; wrote:

>  Dne 27. 06. 19 v 23:56 Zbigniew Jędrzejewski-Szmek napsal(a):
>  > (try to add '--allowerasing' to command line to replace conflicting
>  packages or '--skip-broken' to skip uninstallable packages)
>
>  This is message for people who are willing/are able to fix or report
>  things. For regular user this should be
>    .. or run with "--nobest" to skip broken deps.
>  
Can somebody clarify the difference between --skip-broken and --nobest?
Because even after reading the man page, I still don't get it. And I
believe most our users will not get it either.

[Zbigniew Jędrzejewski-Szmek]

On Fri, Jun 28, 2019 at 02:00:22PM +0200, Kamil Paral wrote:
>  On Fri, Jun 28, 2019 at 11:12 AM Miroslav Suchý
> <msuchy(a)redhat.com&gt; wrote:
>  
>  > Dne 27. 06. 19 v 23:56 Zbigniew Jędrzejewski-Szmek napsal(a):
>  > > (try to add '--allowerasing' to command line to replace conflicting
>  > packages or '--skip-broken' to skip uninstallable packages)
>  >
>  > This is message for people who are willing/are able to fix or report
>  > things. For regular user this should be
>  >   .. or run with "--nobest" to skip broken deps.
>  >
>  
>  Can somebody clarify the difference between --skip-broken and --nobest?
>  Because even after reading the man page, I still don't get it. And I
>  believe most our users will not get it either. 
--nobest means: consider older versions of packages for installation, don't insist on
upgrading everything.
--skip-broken means: skip packages which were selected but cannot be installed, instead of
erroring out.

At least that's how I understand it.

Zbyszek

[Petr Pisar]

On 2019-06-27, Ben Cotton <bcotton(a)redhat.com&gt; wrote:
>  https://fedoraproject.org/wiki/Changes/DNF_Default_Best
>
> == Summary ==
>  Currently, DNF prefers clean dependency resolution over package
>  updates; a package (almost) silently won't get updated to a newer
>  version if the new version has dependency problems. DNF will be
>  changed to prefer updates and fail if they have dependency resolution
>  issues, while the failure has a temporal or permanent workaround hint
>  for users who want to use the older behavior.
>  
This will also apply to DNF in Koji. And that will complicate
bootstrapping Perl ecosystem. We will probably cope with the change by
adding another step to the process of boostrapping Perl.

Nevertheless I have a question whether the "best" strategy applies to
package NEVRAs only or if it also applies to Provides and Requires. E.g.
if a

package A provides FOO = 1

and a

package B provides FOO = 2,

will installing FOO insist on installing package B or will it keep
freedom to choose between A and B?

-- Petr

[Jaroslav Mracek]

On Fri, Jun 28, 2019 at 10:35 AM Petr Pisar <ppisar(a)redhat.com&gt; wrote:

>  On 2019-06-27, Ben Cotton <bcotton(a)redhat.com&gt; wrote:
>  > https://fedoraproject.org/wiki/Changes/DNF_Default_Best
>  >
>  >== Summary ==
>  > Currently, DNF prefers clean dependency resolution over package
>  > updates; a package (almost) silently won't get updated to a newer
>  > version if the new version has dependency problems. DNF will be
>  > changed to prefer updates and fail if they have dependency resolution
>  > issues, while the failure has a temporal or permanent workaround hint
>  > for users who want to use the older behavior.
>  >
>  This will also apply to DNF in Koji. And that will complicate
>  bootstrapping Perl ecosystem. We will probably cope with the change by
>  adding another step to the process of boostrapping Perl.
>
>  Nevertheless I have a question whether the "best" strategy applies to
>  package NEVRAs only or if it also applies to Provides and Requires. E.g.
>  if a
>
>  package A provides FOO = 1
>
>  and a
>
>  package B provides FOO = 2,
>
>  will installing FOO insist on installing package B or will it keep
>  freedom to choose between A and B?
>  
If you request Package A you will always get package A. If you will request
package in lover version, you will get the package in requested version.

Jaroslav


>  -- Petr
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