Rel4tion-Wiki/maint/admin/Git_Server/Mirrors.mdwn

Sometimes it's useful to have a repository on your server, which simply mirrors
some other repository, on another server. Maybe it's easier for you to work with
it like that, and create forks. Or the repository you want to use it hosted on
a problematic server, e.g. a centralized hosting service, and you want to make
the code available on an independent 100% free software powered system.

# General Procedure

In general, when creating a local personal mirror outside of Gitolite, the
following procedure works.

Create the repo:

	git init --bare

Configure it:

	git remote add origin URL-HERE
	git config remote.origin.fetch +refs/*:refs/*
	git config fetch.prune true

Run every hour/day/week to update the mirror:

	git fetch --quiet origin

# G1thub

However, Github has additional refs for pull requests, which can create a lot of
unnecessary clutter and increase repo size.

The following approach avoid them. However, it misses some namespaces git uses,
such as notes and replacements. Most of the time they're not used anyway so I
guess it's reasonable. Also, personally, most of the time I don't interact with
Github. Anyway these namespaces can be added manually to the configuration if
needed.

The commands would be as follows.

Create the repo:

	git init --bare

Configure it:

	git remote add origin URL-HERE
	git config remote.origin.fetch +refs/heads/*:refs/heads/*
	git config --add remote.origin.fetch +refs/tags/*:refs/tags/*
	git config fetch.prune true

Run every hour/day/week to update the mirror:

	git fetch --quiet origin

# Gitolite

Now let's see how it's done on a gitolite server.

Create new empty repo (through gitolite-admin, as described in the previous
sections of this guide).

Become the git user (`# su - git`), go to the repository
(`cd /home/git/repositories/my-mirror.git`) and apply the configuration commands
on it as listed above (you can use the G1thub specific ones if you mirror a
G1thub repo).

Write a simple mirror.sh script to run the periodic update command:

	#!/bin/bash
	
	BASE=/home/git/repositories
	
	cd $BASE/my-mirror.git
	git fetch --quiet origin

If you have several mirrors, you can extend the script to loop over them and run
the git fetch command for each. Example:

	#!/bin/bash
	
	BASE=/home/git/repositories
	EXT=.git
	
	MIRRORS="
		bicon
		4store
		raptor
		rasqal
		librdf
		redland-bindings
		redlandpp
	"
	
	for repo in $MIRRORS
	do
		cd ${BASE}/${repo}${EXT}
		git fetch --quiet origin
	done

Another option is to go over all repositories, and use git-config to determine
whether a repository is a mirror, e.g. by checking whether *gitweb.category*
begins with "Mirror". But then you nee to make sure you assign gitweb categories
consistently.

Now become the git user and setup a cron job to run the script periodically
(`crontab -e -u git`):

	# mail any output to `joe', no matter whose crontab this is
	MAILTO=joe
	# m h dom mon dow command
	# run at 4 AM every day
	00 04 * * *       /home/git/mirror.sh

`crontab` opens your default text editor (e.g. nano or vim) and lets you add the
new job. Simply append it to the end of the file.

If you never used nano or vim - maybe it's time to learn, at least the basics.
nano is quite simple: Ctrl-O saves, Ctrl-X quits. To learn the basics of vim,
try `vimtutor`. For simple use it's enough to learn how to insert and delete
text, how to save and how to quit. Summary:

- hjkl or arror keys - navigate
- `i` - (insert mode) type text at cursor position, delete with Backspace
- Esc - stop insert mode (or any other mode, and go back to main mode)
- `:w` Enter - save
- `:q!` Enter - quit without saving
- `:wq` Enter - quit and save

Of course you can make Gedit or Kate etc. your default text editor, but then
you'll be clueless when working on a GUI-less server or using SSH or when things
crash. It's good to have a basic tool which is always available.

If you want to read the e-mail sent to you (user *joe*) by cron, add a "local
mbox" account to your e-mail client, and configure it to read from the file
`/var/mail/joe`.