Remote tracking branches, and how they work.

• master: local tracking branch (in local object store)
• origin/master: remote tracking branch (in local object store)
• master on remote system: remote branch

All of these branches can be “out of sync” with one another.

Examples using the Linux kernel source repository.

$ git status
On branch master
Your branch is up to date with 'origin/master'.

nothing to commit, working tree clean
$

Local tracking branch:

$ git show master
commit 1c163f4c7b3f621efff9b28a47abb36f7378d783 (HEAD -> master, tag: v5.0, origin/master, origin/HEAD)
Author: Linus Torvalds <torvalds@linux-foundation.org>
Date:   Sun Mar 3 15:21:29 2019 -0800

    Linux 5.0

diff --git a/Makefile b/Makefile
index ac5ac28a24e9..d5713e7b1e50 100644
--- a/Makefile
+++ b/Makefile
@@ -2,7 +2,7 @@
 VERSION = 5
 PATCHLEVEL = 0
 SUBLEVEL = 0
-EXTRAVERSION = -rc8
+EXTRAVERSION =
 NAME = Shy Crocodile
 
 # *DOCUMENTATION*
$

Corresponding remote tracking branch:

$ git show origin/master
commit 1c163f4c7b3f621efff9b28a47abb36f7378d783 (HEAD -> master, tag: v5.0, origin/master, origin/HEAD)
Author: Linus Torvalds <torvalds@linux-foundation.org>
Date:   Sun Mar 3 15:21:29 2019 -0800

    Linux 5.0

diff --git a/Makefile b/Makefile
index ac5ac28a24e9..d5713e7b1e50 100644
--- a/Makefile
+++ b/Makefile
@@ -2,7 +2,7 @@
 VERSION = 5
 PATCHLEVEL = 0
 SUBLEVEL = 0
-EXTRAVERSION = -rc8
+EXTRAVERSION =
 NAME = Shy Crocodile
 
 # *DOCUMENTATION*
$

Fetch, but do not merge, which updates the remote tracking branch, but not the local tracking branch:

$ git fetch
remote: Counting objects: 53547, done.
remote: Compressing objects: 100% (20826/20826), done.
remote: Total 53547 (delta 38450), reused 43614 (delta 32435)
Receiving objects: 100% (53547/53547), 41.90 MiB | 11.16 MiB/s, done.
Resolving deltas: 100% (38450/38450), done.
From https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux
   1c163f4c7b3f..1fc1cd8399ab  master     -> origin/master
$

git status will now show that you are considerably behind the remote tracking branch:

$ git status
On branch master
Your branch is behind 'origin/master' by 6622 commits, and can be fast-forwarded.
  (use "git pull" to update your local branch)

nothing to commit, working tree clean
$

And you can show the tip of origin/master:

$ git show origin/master
commit 1fc1cd8399ab5541a488a7e47b2f21537dd76c2d (origin/master, origin/HEAD)
Merge: abf7c3d8ddea 6a613d24effc
Author: Linus Torvalds <torvalds@linux-foundation.org>
Date:   Thu Mar 7 10:11:41 2019 -0800

    Merge branch 'for-5.1' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup
    
    Pull cgroup updates from Tejun Heo:
    
     - Oleg's pids controller accounting update which gets rid of rcu delay
       in pids accounting updates
    
     - rstat (cgroup hierarchical stat collection mechanism) optimization
    
     - Doc updates
    
    * 'for-5.1' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup:
      cpuset: remove unused task_has_mempolicy()
      cgroup, rstat: Don't flush subtree root unless necessary
      cgroup: add documentation for pids.events file
      Documentation: cgroup-v2: eliminate markup warnings
      MAINTAINERS: Update cgroup entry
      cgroup/pids: turn cgroup_subsys->free() into cgroup_subsys->release() to fix the accounting
$

You can treat a remote tracking branch just like any other branch in that you can look, compare, cherry-pick and so on, but you can't check it out to make changes to it:

$ git checkout origin/master
Checking out files: 100% (6413/6413), done.
Note: checking out 'origin/master'.

You are in 'detached HEAD' state. You can look around, make experimental
changes and commit them, and you can discard any commits you make in this
state without impacting any branches by performing another checkout.

If you want to create a new branch to retain commits you create, you may
do so (now or later) by using -b with the checkout command again. Example:

  git checkout -b <new-branch-name>

HEAD is now at 1fc1cd8399ab Merge branch 'for-5.1' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup
$

If you want to incorporate all of that into your local tracking branch, you can just:

$ git checkout master
$ git merge origin/master