openSUSE:Removing update-alternatives support

Removing update-alternatives support

The following guide describes the steps necessary to remove update-alternatives from a given spec file.

This is the first step towards a migration from update-alternatives to any other technical solution we have at the moment.

It’s documented separately as it’s a prerequisite for these other solutions.

Remove the dependencies on update-alternatives

As we won’t be requiring update-alternatives anymore, we must remove any mention of it from the dependencies.

Anything such as the following should be removed:

BuildRequires:         update-alternatives
Requires:              update-alternatives

BuildRequires(post):   update-alternatives
Requires(post):        update-alternatives

BuildRequires(postun): update-alternatives
Requires(postun):      update-alternatives

Suggests:              update-alternatives

Recommends:            update-alternatives

Remove the symlinks update-alternatives requires in the %install section

As update-alternatives requires a certain symlink structure to work properly, and these are typically defined in the %install section, we must remove them.

The following example was taken from the transmission package, adapt as needed.

The %install script would be creating the following structure:

# this is the directory that controls which alternatives are currently chosen/selected
# the script creates this directory as it may not have been previously created by another package, just to be sure
mkdir /etc/alternatives

# this creates the symlink that will act as the regular executable (/usr/bin/transmission)
# it's linked back to /etc/alternatives/transmission so that by changing that symlink, we indirectly control
# what /usr/bin/transmission invokes, when executed
ln -s -f /etc/alternatives/transmission %{buildroot}/usr/bin/transmission

# and the same applies to the man page
ln -s -f /etc/alternatives/transmission.1.gz %{buildroot}/usr/share/man/man1/transmission.1.gz

So basically just delete these lines. But make sure you understand what’s happening, of course.

%install
mkdir -p %{buildroot}%{_sysconfdir}/alternatives

ln -s -f %{_sysconfdir}/alternatives/transmission \
         %{buildroot}/%{_bindir}/transmission

ln -s -f %{_sysconfdir}/alternatives/transmission.1.gz \
         %{buildroot}/%{_mandir}/man1/transmission.1.gz

Remove all the %post and %postun scripts related to update-alternatives

Again, this example is from the transmission package, adapt as needed.

These scripts won’t be required anymore, as there will be no more state (symlinks and files) related to update-alternatives on the filesystem anymore.

Basically, each subpackage (-qt, -gtk, -cli, etc) will have its own %post and %postun scripts. These register the alternative when the package is installed, and remove it when it is uninstalled. As we won’t be using update-alternatives anymore, there’s no sense in keeping these scripts in the spec file.

This is from the transmission-cli subpackage, from the same spec file. Notice the priority 5 here. We’ll be keeping this same priority if we migrate to libalternatives. We don’t want to lose that priority, so make a note if you plan on migrating to libalternatives.

%post
update-alternatives \
    --install %{_bindir}/transmission transmission \
              %{_bindir}/transmission-cli 5 \
    --slave   %{_mandir}/man1/transmission.1.gz transmission.1.gz \
              %{_mandir}/man1/transmission-cli.1.gz

%postun
# Note: we don't use "$1 -eq 0", to avoid issues if the package gets renamed
if [ ! -f %{_bindir}/transmission-cli ]; then
    update-alternatives --remove transmission %{_bindir}/transmission-cli
fi

And this is from the transmission-gtk subpackage, from the same spec file. Notice the priority 15 here. We’ll be keeping this same priority if we migrate to libalternatives.

%post
update-alternatives \
    --install %{_bindir}/transmission transmission \
              %{_bindir}/transmission-gtk 15 \
    --slave   %{_mandir}/man1/transmission.1.gz transmission.1.gz \
              %{_mandir}/man1/transmission-gtk.1.gz

%postun gtk
# Note: we don't use "$1 -eq 0", to avoid issues if the package gets renamed
if [ ! -f %{_bindir}/transmission-gtk ]; then
    update-alternatives --remove transmission %{_bindir}/transmission-gtk
fi

Adjust the %files section

We must now remove the related files from the %files section.

For any subpackage that lists the structure in its %files section, we simply delete those lines:

%ghost %{_sysconfdir}/alternatives/%{name}       # executable
%ghost %{_sysconfdir}/alternatives/%{name}.1.gz  # man page

As a reminder, for each subpackage, these lines would have been expanded as follows:

# -cli subpackage
%ghost /etc/alternatives/transmission       # executable
%ghost /etc/alternatives/transmission.1.gz  # man page

# -gtk subpackage
%ghost /etc/alternatives/transmission       # executable
%ghost /etc/alternatives/transmission.1.gz  # man page

Decide on a migration strategy for the package

The package should now be free from update-alternatives. We have:

1. Removed its dependencies on the update-alternatives package.
2. Removed the initial filesystem structure creation in the %install section.
3. Removed all of its %post and %postun scripts related to update-alternatives.
4. Removed all the related files from the %files section.

Naturally, the next step that follows is deciding what to do with the package next.

Here are the solutions we currently support:

• Migrating to libalternatives by leveraging the alts package.
• Migrating to libalternatives through a custom executable.
• Migrating to a conflict-based implementation