报错与处理过程：
$ git push
Counting objects: 21, done.
Delta compression using up to 8 threads.
Compressing objects: 100% (21/21), done.
Writing objects: 100% (21/21), 2.78 KiB | 0 bytes/s, done.
Total 21 (delta 14), reused 0 (delta 0)
remote: error: cannot lock ref 'refs/heads/master': Unable to create '/var/opt/gitlab/git-data-file11/repositories/tomfriwel/test.git/./refs/heads/master.lock': File exists.
remote:
remote: Another git process seems to be running in this repository, e.g.
remote: an editor opened by 'git commit'. Please make sure all processes
remote: are terminated then try again. If it still fails, a git process
remote: may have crashed in this repository earlier:
remote: remove the file manually to continue.
To gitlab.com:tomfriwel/test.git
! [remote rejected] master -> master (failed to update ref)
error: failed to push some refs to 'git@gitlab.com:tomfriwel/test.git'
$ rm -f /var/opt/gitlab/git-data-file11/repositories/tomfriwel/test.git/./refs/heads/master.lock
$ git push
将报错中提示的文件删除，再push就行了。
