三行代码实现新老git仓库完整迁移

#从老gitlib拉取裸仓库，并在本地文件系统创建gitbook-demo.git文件夹
git clone --bare ssh://git@oldgitlab:12345/group1/gitbook-demo.git
#进入代码目录
cd gitbook-demo.git
#向新git推送镜像
git push --mirror ssh://git@newgitlab:67890/group1/gitbook-demo.git

#官网的解释 Git - git-clone Documentation (git-scm.com)
--bare
Make a bare Git repository. That is, instead of creating <directory> and placing the administrative 
files in <directory>/.git, make the <directory> itself the $GIT_DIR. This obviously implies the 
--no-checkout because there is nowhere to check out the working tree. Also the branch heads at the 
remote are copied directly to corresponding local branch heads, without mapping them to
refs/remotes/origin/. When this option is used, neither remote-tracking branches nor the related 
configuration variables are created.

.
+--- config
+--- description
+--- HEAD
+--- hooks
|   +--- applypatch-msg.sample
|   +--- commit-msg.sample
|   +--- fsmonitor-watchman.sample
|   +--- post-update.sample
|   +--- pre-applypatch.sample
|   +--- pre-commit.sample
|   +--- pre-push.sample
|   +--- pre-rebase.sample
|   +--- pre-receive.sample
|   +--- prepare-commit-msg.sample
|   +--- update.sample
+--- info
|   +--- exclude
+--- objects
|   +--- info
|   +--- pack
|   |   +--- pack-bcbf9435c77edd5760bc9fcd1897c93317b379ab.idx
|   |   +--- pack-bcbf9435c77edd5760bc9fcd1897c93317b379ab.pack
+--- packed-refs
+--- refs
|   +--- heads
|   +--- tags

+--- COMMIT_EDITMSG
+--- config
+--- FETCH_HEAD
+--- HEAD
+--- index
+--- logs
|   +--- HEAD
|   +--- refs
|   |   +--- heads
|   |   |   +--- master
|   |   +--- remotes
|   |   |   +--- origin
|   |   |   |   +--- HEAD
|   |   |   |   +--- master
+--- objects
|   +--- 0a
|   |   +--- 5349217075b4e65f23f1fc6047bd88b3bc408a
|   +--- 0f
|   |   +--- ea4d6af00e21b71a3d35e5a830e69c09f2a899
|   |   +--- f1fa62af96492f849b465019cf887fc1bf05ec
|   +--- 11
|   |   +--- 327b90d92796e1584c91316c355c119b8f87f5
|   |   +--- bb6a4b917bb7706244d9369b9fb3cac7277752
|   +--- ff
|   |   +--- 5af373a9c41390ddbc3915978e029d9d298d29
|   +--- info
|   +--- pack
|   |   +--- pack-e872e830762b5b1425d3c782702da0646697165f.idx
|   |   +--- pack-e872e830762b5b1425d3c782702da0646697165f.pack
+--- ORIG_HEAD
+--- packed-refs
+--- refs
|   +--- heads
|   |   +--- master
|   +--- remotes
|   |   +--- origin
|   |   |   +--- HEAD
|   |   |   +--- master
|   +--- tags
+--- sourcetreeconfig

[core]
    repositoryformatversion = 0
    filemode = false
    bare = true
    symlinks = false
    ignorecase = true
[remote "origin"]
    url = ssh://git@oldgitlab:12345/platform/gitbook-demo.git
——————————————————————————————————————↑↑↑↑↑↑↑↑↑↑↑↑裸仓库config文件↑↑↑↑↑↑↑↑↑↑↑↑↑↑————————————————————————————————————————————
——————————————————————————————————————↓↓↓↓↓↓↓↓↓↓↓↓↓↓非裸仓库./.git/config文件↓↓↓↓↓↓↓↓↓↓↓↓————————————————————————————————————————————
[core]
    repositoryformatversion = 0
    filemode = false
    bare = false
    logallrefupdates = true
    symlinks = false
    ignorecase = true
[remote "origin"]
    url = ssh://git@oldgitlab:12345/platform/gitbook-demo.git
    fetch = +refs/heads/*:refs/remotes/origin/*
[branch "master"]
    remote = origin
    merge = refs/heads/master
[gui]
    wmstate = normal
    geometry = 835x475+225+225 185 214

Instead of naming each ref to push, specifies that all refs under refs/ (which includes but is not
 limited to refs/heads/, refs/remotes/, and refs/tags/) be mirrored to the remote repository. 
 Newly created local refs will be pushed to the remote end, locally updated refs will be force
  updated on the remote end, and deleted refs will be removed from the remote end. This is the
   default if the configuration option remote.<remote>.mirror is set.
#简单点说就是所有引用会以自己为主，强制推送到远程