Packaging:Alternatives

= Alternatives =

What are alternatives
Alternatives provide means for parallel installation of packages which provide the same functionality by maintaining sets of symlinks (one per package) pointing to alternativized files like this: For more information, see  manpage.

Recommended usage
Alternatives can be used to allow parallel installation of software that can be used as a drop-in replacement and functions with sufficient similarity that users and other programs would, within reason, not need to know which variant is currently installed (for example: the various MTAs which all provide ). Selection of which of the parallel-installed packages to use for a given alternativized file can only be done system-wide by a root-level user. Alternatives are not recommended to facilitate parallel installation of software whose selection should be done by users (for example: the various MPI environments).

How to use alternatives
If a package is using alternatives, the files which would otherwise conflict must be installed with an appropriate suffix (for example:  instead of  ), the original locations must be touched (for example:  ), the links set up by alternatives must be listed as %ghost in the file list and proper Requires: must be added, like in the examples below.

Putting the alternativized files in the file list ensures that they are owned by respective packages, which means that commands like: all work properly. Using %ghost for this purpose allows using globs and generated file lists.
 * rpm -qf /usr/bin/foo
 * yum install /usr/bin/foo
 * repoquery --whatprovides /usr/bin/foo

Examples
Example from antlr.spec: Requires(post): %{_sbindir}/update-alternatives Requires(postun): %{_sbindir}/update-alternatives ... %install ... touch %{buildroot}%{_bindir}/antlr

%post %{_sbindir}/update-alternatives --install %{_bindir}/antlr \ %{name} %{_bindir}/antlr-java 10

%postun if [ $1 -eq 0 ] ; then %{_sbindir}/update-alternatives --remove %{name} %{_bindir}/antlr-java fi ... %files ... %ghost %{_bindir}/antlr %{_bindir}/antlr-java

And a more complex example of alternatives invocation from sendmail.spec, slightly edited: Requires(post): %{_sbindir}/update-alternatives Requires(postun): %{_sbindir}/update-alternatives Requires(preun): %{_sbindir}/update-alternatives ... %install ... mv %{buildroot}%{_sbindir}/sendmail %{buildroot}%{_sbindir}/sendmail.sendmail touch %{buildroot}%{_sbindir}/sendmail for i in mailq newaliases rmail; do	mv %{buildroot}%{_bindir}/$i %{buildroot}%{_bindir}/$i.sendmail touch %{buildroot}%{_bindir}/$i done mv %{buildroot}%{_mandir}/man1/mailq.1 %{buildroot}%{_mandir}/man1/mailq.sendmail.1 touch %{buildroot}%{_mandir}/man1/mailq.1 mv %{buildroot}%{_mandir}/man1/newaliases.1 %{buildroot}%{_mandir}/man1/newaliases.sendmail.1 touch %{buildroot}%{_mandir}/man1/newaliases.1 mv %{buildroot}%{_mandir}/man5/aliases.5 %{buildroot}%{_mandir}/man5/aliases.sendmail.5 touch %{buildroot}%{_mandir}/man5/aliases.5 mv %{buildroot}%{_mandir}/man8/sendmail.8 %{buildroot}%{_mandir}/man8/sendmail.sendmail.8 touch %{buildroot}%{_mandir}/man8/sendmail.8
 * 1) rename files for alternative usage

%postun if [ "$1" -ge "1" ]; then if [ "`readlink %{_sysconfdir}/alternatives/mta`" == "%{_sbindir}/sendmail.sendmail" ]; then %{_sbindir}/alternatives --set mta %{_sbindir}/sendmail.sendmail fi fi

%post %{_sbindir}/update-alternatives --install %{_sbindir}/sendmail mta %{_sbindir}/sendmail.sendmail 90 \ --slave %{_bindir}/mailq mta-mailq %{_bindir}/mailq.sendmail \ --slave %{_bindir}/newaliases mta-newaliases %{_bindir}/newaliases.sendmail \ --slave %{_bindir}/rmail mta-rmail %{_bindir}/rmail.sendmail \ --slave /usr/lib/sendmail mta-sendmail /usr/lib/sendmail.sendmail \ --slave %{_sysconfdir}/pam.d/smtp mta-pam %{_sysconfdir}/pam.d/smtp.sendmail \ --slave %{_mandir}/man8/sendmail.8.gz mta-sendmailman %{_mandir}/man8/sendmail.sendmail.8.gz \ --slave %{_mandir}/man1/mailq.1.gz mta-mailqman %{_mandir}/man1/mailq.sendmail.1.gz \ --slave %{_mandir}/man1/newaliases.1.gz mta-newaliasesman %{_mandir}/man1/newaliases.sendmail.1.gz \ --slave %{_mandir}/man5/aliases.5.gz mta-aliasesman %{_mandir}/man5/aliases.sendmail.5.gz \ --initscript sendmail ...
 * 1) Set up the alternatives files for MTAs.

%preun if [ $1 = 0 ]; then %{_sbindir}/update-alternatives --remove mta %{_sbindir}/sendmail.sendmail fi ...

%files ... %ghost %{_sbindir}/sendmail %ghost %{_bindir}/mailq %ghost %{_bindir}/newaliases %ghost %{_bindir}/rmail %ghost /usr/lib/sendmail %ghost %{_sysconfdir}/pam.d/smtp %ghost %{_mandir}/man8/sendmail.8.gz %ghost %{_mandir}/man1/mailq.1.gz %ghost %{_mandir}/man1/newaliases.1.gz %ghost %{_mandir}/man5/aliases.5.gz

%{_sbindir}/sendmail.sendmail %{_bindir}/mailq.sendmail %{_bindir}/newaliases.sendmail %{_bindir}/rmail.sendmail /usr/lib/sendmail.sendmail %config(noreplace) %{_sysconfdir}/pam.d/smtp.sendmail %{_mandir}/man8/sendmail.sendmail.8.gz %{_mandir}/man1/mailq.sendmail.1.gz %{_mandir}/man1/newaliases.sendmail.1.gz %{_mandir}/man5/aliases.sendmail.5.gz

%attr(0755,root,root) %{_initrddir}/sendmail