Preliminary work on tweaking the git plugin to checkout to an optional local branch (for JENKINS-6856 as well as this) is up at http://github.com/abayer/Hudson-GIT-plugin/tree/JENKINS-6856, if anyone wants to take a look.

Sending this back to m2release - it should work now from the git plugin side of things.

Still not working, relavent sections are:

<pre>
Checkout:proj-app_commit / /home/hudson/data/workspace/proj-app_commit - hudson.remoting.Channel@1c17335:cabci-cf-rh5-x64-01
Using strategy: Default
Last Built Revision: Revision ec90272fc4b0def86159148588e4f9d602b256dc (origin/master)
Checkout:proj-app_commit / /home/hudson/data/workspace/proj-app_commit - hudson.remoting.LocalChannel@a90942
GitAPI created
Fetching changes from the remote Git repository
Fetching upstream changes from ssh://user@mygerritserver:29418/cms/proj/proj-app.git
[proj-app_commit] $ git fetch -t ssh://user@mygerritserver:29418/cms/proj/proj-app.git +refs/heads/:refs/remotes/origin/
[proj-app_commit] $ git ls-tree HEAD
Seen branch in repository origin/master
Commencing build of Revision ec90272fc4b0def86159148588e4f9d602b256dc (origin/master)
GitAPI created
Checking out Revision ec90272fc4b0def86159148588e4f9d602b256dc (origin/master)
[proj-app_commit] $ git checkout -f ec90272fc4b0def86159148588e4f9d602b256dc
[proj-app_commit] $ git tag -a -f -m "Hudson Build #36" hudson-proj-app_commit-36
Recording changes in branch origin/master
[proj-app_commit] $ git whatchanged --no-abbrev -M --pretty=raw ec90272fc4b0def86159148588e4f9d602b256dc..ec90272fc4b0def86159148588e4f9d602b256dc
Parsing POMs

<snip>

[INFO] Executing: /bin/sh -c cd /home/hudson/data/workspace/proj-app_commit && git add pom.xml proj-bp/pom.xml proj-bp/proj-bp-adiSupport/pom.xml proj-bp/proj-bp-content/pom.xml proj-bp/proj-bp-offer/pom.xml proj-bp/proj-bp-offer/proj-bp-offer-base/pom.xml proj-bp/proj-bp-offer/proj-bp-offer-interface/pom.xml proj-bp/proj-bp-offer/proj-bp-offer-mercury/pom.xml proj-bp/proj-bp-offer/proj-bp-offer-mock/pom.xml proj-bp/proj-bp-offer/proj-bp-offer-xti/pom.xml proj-bp/proj-bp-publishing/pom.xml proj-bp/proj-bp-publishing/proj-bp-publishing-base/pom.xml proj-bp/proj-bp-publishing/proj-bp-publishing-interface/pom.xml proj-bp/proj-bp-publishing/proj-bp-publishing-mercury/pom.xml proj-bp/proj-bp-publishing/proj-bp-publishing-mock/pom.xml proj-bp/proj-bp-publishing/proj-bp-publishing-xti/pom.xml proj-definitions/pom.xml proj-definitions/proj-definitions-commonSpring/pom.xml proj-definitions/proj-definitions-packWorkflow/pom.xml proj-definitions/proj-definitions-classificationWorkflow/pom.xml proj-definitions/proj-definitions-ingestWorkflow/pom.xml proj-platform/pom.xml proj-platform/proj-platform-dataEventNotifier/pom.xml proj-platform/proj-platform-workflowSupport/pom.xml proj-platform/proj-platform-status/pom.xml proj-externals/pom.xml proj-externals/proj-externals-gateway/pom.xml proj-platform/proj-platform-applicationHost/pom.xml proj-packaging/pom.xml
[INFO] Working directory: /home/hudson/data/workspace/proj-app_commit
[INFO] Executing: /bin/sh -c cd /home/hudson/data/workspace/proj-app_commit && git status
[INFO] Working directory: /home/hudson/data/workspace/proj-app_commit
[INFO] Executing: /bin/sh -c cd /home/hudson/data/workspace/proj-app_commit && git commit --verbose -F /tmp/maven-scm-1512028766.commit pom.xml proj-bp/pom.xml proj-bp/proj-bp-adiSupport/pom.xml proj-bp/proj-bp-content/pom.xml proj-bp/proj-bp-offer/pom.xml proj-bp/proj-bp-offer/proj-bp-offer-base/pom.xml proj-bp/proj-bp-offer/proj-bp-offer-interface/pom.xml proj-bp/proj-bp-offer/proj-bp-offer-mercury/pom.xml proj-bp/proj-bp-offer/proj-bp-offer-mock/pom.xml proj-bp/proj-bp-offer/proj-bp-offer-xti/pom.xml proj-bp/proj-bp-publishing/pom.xml proj-bp/proj-bp-publishing/proj-bp-publishing-base/pom.xml proj-bp/proj-bp-publishing/proj-bp-publishing-interface/pom.xml proj-bp/proj-bp-publishing/proj-bp-publishing-mercury/pom.xml proj-bp/proj-bp-publishing/proj-bp-publishing-mock/pom.xml proj-bp/proj-bp-publishing/proj-bp-publishing-xti/pom.xml proj-definitions/pom.xml proj-definitions/proj-definitions-commonSpring/pom.xml proj-definitions/proj-definitions-packWorkflow/pom.xml proj-definitions/proj-definitions-classificationWorkflow/pom.xml proj-definitions/proj-definitions-ingestWorkflow/pom.xml proj-platform/pom.xml proj-platform/proj-platform-dataEventNotifier/pom.xml proj-platform/proj-platform-workflowSupport/pom.xml proj-platform/proj-platform-status/pom.xml proj-externals/pom.xml proj-externals/proj-externals-gateway/pom.xml proj-platform/proj-platform-applicationHost/pom.xml proj-packaging/pom.xml
[INFO] Working directory: /home/hudson/data/workspace/proj-app_commit
[INFO] Executing: /bin/sh -c cd /home/hudson/data/workspace/proj-app_commit && git push
[INFO] Working directory: /home/hudson/data/workspace/proj-app_commit
[TASKS] Skipping non-existent folder '/home/hudson/data/workspace/proj-app_commit/src/main/java'...
[TASKS] Skipping non-existent folder '/home/hudson/data/workspace/proj-app_commit/src/test/java'...
[TASKS] Skipping non-existent folder '/home/hudson/data/workspace/proj-app_commit/src/main/resources'...
[TASKS] Skipping non-existent folder '/home/hudson/data/workspace/proj-app_commit/src/test/resources'...
[HUDSON] Archiving /home/hudson/data/workspace/proj-app_commit/pom.xml to /home/hudson/data/jobs/proj-app_commit/modules/com.myco.myproj$proj-app/builds/2010-09-07_15-59-14/archive/com.myco.myproj/proj-app/0.0.1-1-SNAPSHOT/pom.xml
[INFO] ------------------------------------------------------------------------
[ERROR] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Unable to commit files
Provider message:
The git-push command failed.
Command output:
To ssh://user@mygerritserver:29418/cms/proj/proj-app.git
! [rejected] master -> master (non-fast-forward)
error: failed to push some refs to 'ssh://user@mygerritserver:29418/cms/proj/proj-app.git'
To prevent you from losing history, non-fast-forward updates were rejected
Merge the remote changes (e.g. 'git pull') before pushing again. See the
'Note about fast-forwards' section of 'git push --help' for details.
</pre>

This is working if you set the Git plugin setting to merge before build (whatever that does?)

no it's not as the modified poms don't get commited back in as we seem to be on a local branch.

This is working if I use the m2 extra steps plugin and the following config

Git
"Merge before build" origin, master

And m2 extra steps (pre-build)
git checkout master || git checkout -b master
git reset --hard origin/master

I see the same thing. By default, the workspace is in (no branch).

If I manually run

mvn -X -B -f /[jenkins]/jobs/[job]/workspace/pom.xml -Dresume=false release:prepare release:perform

.. it ends with a

org.apache.maven.scm.ScmException: Detecting the current branch failed: fatal: ref HEAD is not a symbolic ref

If I first do a 'git checkout master', and then repeat the command it works fine.

Back in Jenkins, I then configured the job's - SCM section with Branch Specifier: "master", and under Advanced I entered Checkout/merge to local branch (optional): "master"

After that it works fine. Still, it's a bit annoying that it didn't work by default. I don't know if this is the fault of the maven-release-plugin (should it be possible to make a release when not on a branch?).. but not having to configure this for each job would be nice.

I'm facing the same issue as tfnico with 1.409.2 and git plugin 1.1.12

git plugin does checkout commits by RefID, not branches. You can force it to use a local branch (advanced section) so that maven release process will be able to commit, tag and push to remote repository

What is the reason behind that decision? Why does it not check out the branch?

This is especially confusing as you already were branch-specific when specifying the branch specifier.
When you specify the job shall build master, why does it not check out master?