Jenkins Git plugin detached HEAD

I am new to Git and also to Jenkins. My problem is that I can't get the Jenkins Maven release plugin to work.

When I build a common Maven build with Jenkins, it works well, but when I try to perform a release with the Maven release plugin, I get the following stack trace:

org.apache.maven.lifecycle.LifecycleExecutionException: Failed to execute goal org.apache.maven.plugins:maven-release-plugin:2.3.2:prepare (default-cli) on project parent: An error is occurred in the checkin process: Exception while executing SCM command.
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:217)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:153)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:145)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:84)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:59)
    at org.apache.maven.lifecycle.internal.LifecycleStarter.singleThreadedBuild(LifecycleStarter.java:183)
    at org.apache.maven.lifecycle.internal.LifecycleStarter.execute(LifecycleStarter.java:161)
    at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:320)
    at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:156)
    at org.jvnet.hudson.maven3.launcher.Maven3Launcher.main(Maven3Launcher.java:79)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at org.codehaus.plexus.classworlds.launcher.Launcher.launchStandard(Launcher.java:329)
    at org.codehaus.plexus.classworlds.launcher.Launcher.launch(Launcher.java:239)
    at org.jvnet.hudson.maven3.agent.Maven3Main.launch(Maven3Main.java:158)
    at hudson.maven.Maven3Builder.call(Maven3Builder.java:98)
    at hudson.maven.Maven3Builder.call(Maven3Builder.java:64)
    at hudson.remoting.UserRequest.perform(UserRequest.java:118)
    at hudson.remoting.UserRequest.perform(UserRequest.java:48)
    at hudson.remoting.Request$2.run(Request.java:326)
    at hudson.remoting.InterceptingExecutorService$1.call(InterceptingExecutorService.java:72)
    at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
    at java.util.concurrent.FutureTask.run(FutureTask.java:138)
    at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
    at java.lang.Thread.run(Thread.java:662)
Caused by: org.apache.maven.plugin.MojoExecutionException: An error is occurred in the checkin process: Exception while executing SCM command.
    at org.apache.maven.plugins.release.PrepareReleaseMojo.prepareRelease(PrepareReleaseMojo.java:295)
    at org.apache.maven.plugins.release.PrepareReleaseMojo.execute(PrepareReleaseMojo.java:247)
    at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:101)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:209)
    ... 27 more
Caused by: org.apache.maven.shared.release.ReleaseExecutionException: An error is occurred in the checkin process: Exception while executing SCM command.
    at org.apache.maven.shared.release.phase.AbstractScmCommitPhase.checkin(AbstractScmCommitPhase.java:160)
    at org.apache.maven.shared.release.phase.AbstractScmCommitPhase.performCheckins(AbstractScmCommitPhase.java:145)
    at org.apache.maven.shared.release.phase.ScmCommitPreparationPhase.runLogic(ScmCommitPreparationPhase.java:76)
    at org.apache.maven.shared.release.phase.AbstractScmCommitPhase.execute(AbstractScmCommitPhase.java:78)
    at org.apache.maven.shared.release.DefaultReleaseManager.prepare(DefaultReleaseManager.java:234)
    at org.apache.maven.shared.release.DefaultReleaseManager.prepare(DefaultReleaseManager.java:169)
    at org.apache.maven.shared.release.DefaultReleaseManager.prepare(DefaultReleaseManager.java:146)
    at org.apache.maven.shared.release.DefaultReleaseManager.prepare(DefaultReleaseManager.java:107)
    at org.apache.maven.plugins.release.PrepareReleaseMojo.prepareRelease(PrepareReleaseMojo.java:291)
    ... 30 more
Caused by: org.apache.maven.scm.ScmException: Exception while executing SCM command.
    at org.apache.maven.scm.command.AbstractCommand.execute(AbstractCommand.java:63)
    at org.apache.maven.scm.provider.git.AbstractGitScmProvider.executeCommand(AbstractGitScmProvider.java:291)
    at org.apache.maven.scm.provider.git.AbstractGitScmProvider.checkin(AbstractGitScmProvider.java:217)
    at org.apache.maven.scm.provider.AbstractScmProvider.checkIn(AbstractScmProvider.java:410)
    at org.apache.maven.shared.release.phase.AbstractScmCommitPhase.checkin(AbstractScmCommitPhase.java:156)
    ... 38 more
Caused by: org.apache.maven.scm.ScmException: Detecting the current branch failed: fatal: ref HEAD is not a symbolic ref
    at org.apache.maven.scm.provider.git.gitexe.command.branch.GitBranchCommand.getCurrentBranch(GitBranchCommand.java:147)
    at org.apache.maven.scm.provider.git.gitexe.command.checkin.GitCheckInCommand.createPushCommandLine(GitCheckInCommand.java:192)
    at org.apache.maven.scm.provider.git.gitexe.command.checkin.GitCheckInCommand.executeCheckInCommand(GitCheckInCommand.java:132)
    at org.apache.maven.scm.command.checkin.AbstractCheckInCommand.executeCommand(AbstractCheckInCommand.java:54)
    at org.apache.maven.scm.command.AbstractCommand.execute(AbstractCommand.java:59)
    ... 42 more
channel stopped
Finished: FAILURE

The failing command and error message are:

[INFO] Executing: /bin/sh -c cd
/var/lib/jenkins/workspace/test_maven/parent && git symbolic-ref HEAD
[INFO]  Working directory:
/var/lib/jenkins/workspace/test_maven/parent  mojoFailed
org.apache.maven.plugins:maven-release-plugin:2.3.2(default-cli)
projectFailed ch.apkern.achilles:parent:1.0-SNAPSHOT  sessionEnded

I have figured out that the Jenkins Git plugin creates a detached HEAD ref "(no branch)" which causes the problem, I think. But I have absolutely no idea why this ref is created or how I can solve this problem.

I would be grateful for any help.

Solution 1:

The Checkout/merge to local branch (optional) field is gone in the current (2.2.1) version of the Git plugin.

It has moved to Additional Behaviours → Check out to specific local branch:

Setting that value to master got me a checked out branch instead of a detached head.

Solution 2:

None of the other answer's Jenkins configurations worked for me without having to create manual steps. What indeed works is plain simple:

Repository URL: <repo>
Branches to build: master
Checkout/merge to local branch (optional): master

Solution 3:

UPDATE (November 2015): Please, note that this solution was given for a specific version of Git plugin (1.1.26). In later versions, the plugin was updated to make configuration easier.

For Jenkins Git plugin version 1.1.26 try this:

Go to Job Configuration. Scroll down to Git section and click "Advanced..." button under "Repositories". Then set:

Name: origin
Refspec: +refs/heads/branch-0.1:refs/remotes/origin/localbranchname

Then click another "Advanced..." button and set:

Checkout/merge to local branch (optional): localbranchname

You can name the local branch as you like, but the destination in Refspec must match the local branch name in that optional field (in this case "localbranchname"). This will attach HEAD to localbranchname like this:

HEAD -> refs/heads/localbranchname -> 7a698457751bdc043cfda631b81e3812c5361790

Maven Release should pass now in Jenkins.

By the way, this works for me with Jenkins 1.492 and Jenkins Git plugin version 1.1.26.