Category Archives: linux

I just had the following conversation with my linux desktop:

Me: “Hi, I’d like to use my new printer please.”

Computer: “Do you mean this HP Laserjet CP1515n on the network?”

Me: “Erm, yes I do.”

Computer: “Good. You’ve got a test page printing as we speak.
Anything else I can help you with?”

Sadly I don’t have any alternative modern operating systems to
compare it to, but having done similar things with linux over the last
12 years, I’m impressed with how far we’ve come. Thank you to everyone
who made this possible.

While git is a completely distributed revision control system, sometimes
the lack of a central canonical repository can be annoying. For example,
you might want to make your repository published publically, so other
people can fork your code, or you might want all your developers to push
into (or have code pulled into) a central “golden” tree, that you then
use for automated building and continuous integration. This entry should
explain how to get this all working on Ubuntu 9.04 (Jaunty).

Gitosis is a very useful git repository manager, which adds support like
ACLs in pre-commits and gitweb and git-daemon management. While it’s
possible to set all these things up by hand, gitosis does everything for
you. It is nicely configured via git; to make configuration changes,
you push the config file changes into gitosis repository on the server.

Gitosis is available in Jaunty, but unfortunately there is a bug
in the version in Jaunty, which means it doesn’t work out of the box.
Fortunately there is a fixed version in jaunty-proposed that
fixes the main problem. This does mean that you need to add the
following to your sources.list:

deb http://gb.archive.ubuntu.com/ubuntu/ jaunty-proposed universe

Run apt-get update && apt-get install gitosis. You should
install 0.2+20080825-2ubuntu0.1 or later. There is another
small bug in the current version too, as a result of git removing the
git-$command scripts out of /usr/bin. Edit
/usr/share/python-support/gitosis/gitosis/templates/admin/hooks/post-update
and replace

git-update-server-info

with

git update-server-info

With these changes in place, we can now set up our gitosis
repository. On the server you are going to use to host your central
repositories, run:

sudo -H -u gitosis gitosis-init < id_rsa.pub

The id_rsa.pub file is a public ssh key. As I mentioned,
gitosis is managed over git, so you need an initial user to clone and
then push changes back into the gitosis repo, so make sure this key
belongs to a keypair you have available to the remote user you’re going
to configure gitosis.

Now, on your local computer, you can clone the gitosis-admin repo
using:

git clone gitosis@gitserver.example.com:gitosis-admin.git

If you look inside the gitosis-admin directory, you should
find a file called gitosis.conf and a directory called
keydir. The directory is where you can add ssh public keys for
your users. The file is the configuration file for gitosis.

[gitosis]
loglevel = INFO

[group gitosis-admin]
writable = gitosis-admin
members = david@david

[group developers]
members = david@david
writable = publicproject privateproject

[group contributors]
members = george@wilber
writable = publicproject

[repo publicproject]
daemon = yes
gitweb = yes

[repo privateproject]
daemon = no
gitweb = no

This sets up two repositories, called publicproject and
privateproject. It enables the public project to be available via the
git protocol and in gitweb if you have that installed. We also create
two groups, developers and contributors. David has access to both
projects, but George only has access to change the publicproject. David
can also modify the gitosis configuration. The users are the names of
ssh keys (the last part of the line in id_dsa.pub or id_rsa.pub).

Once you’ve changed this file, you can run git add
gitosis.conf to add it to the commit, git commit -m "update
gitosis configuration to commit it to your local repository, and
finally git push to push your commits back up into the central
repository. Gitosis should now update the configuration on the server to
match the config file.

One last thing to do is to enable git-daemon, so people can
anonymously clone your projects. Create /etc/event.d/git-daemon with the
following contents:

start on startup
stop on shutdown

exec /usr/bin/git daemon 
   --user=gitosis --group=gitosis 
   --user-path=public-git 
   --verbose 
   --syslog 
   --reuseaddr 
   --base-path=/srv/gitosis/repositories/
respawn

You can now start this using start git-daemon

So now, you need to start using your repository. You can either start
with an existing project or an empty directory. Start by running
git init and then git add $file to add each of the
files you want in your project, and finally git commit to
commit them to your local repository. The final task is to add a remote
repository and push your code into it.

git remote add origin gitosis@gitserver.example.com:privateproject.git
git push origin master:refs/heads/master

In future, you should be able to do git push to push your
changes back into the central repository. You can also clone a project
using git or ssh, providing you have access, using the following
commands. The first is for read-write access over ssh and the second
uses the git protocol for read-only access. The git protocol uses TCP
port 9418, so make sure that’s available externally, if you want the
world to be able to clone your repos.

git clone gitosis@gitserver.example.com:publicproject.git
git clone git://gitserver.example.com/publicproject.git

Setting up GitWeb is left as an exercise for the reader (and myself
because I am yet to attempt to set that up).

Recently, I’ve seen a lot of suggestions along the lines of:

find . -name foo -exec ls -l {} ;

This is incredibly inefficient, because for each and every matching
file, ls will be executed. Fortunately, we can do better by
using xargs. xargs takes a list of lines from stdin
and uses them to build up a command line. It takes special care to not
exceed the maximum command line length by splitting the input up into
multiple commands if it is needed. So, with that knowledge, we can
replace our original command with:

find . -name foo | xargs ls -l

There is one slight problem with this command; it isn’t space-safe.
xargs splits arguments on whitespace, so “file name” will be
incorrectly passed to the command as “file” “name”. Fortunately,
xargs has an option to delimit parameters by the null
character, and as our luck would have it, find has a suitable
option to produce output in this format. This means our command is
now:

find . -name foo -print0 | xargs -0 ls -l

mlocate can do something similar:

locate foo -0 | xargs -0 ls -l

GNU find has one more trick up its sleeve. It has a modified version
of -exec that will do the same thing as xargs, so we could have
written our original command as:

find . -name foo -exec ls -l {} +

Every process is sacred; every process is great. If a process is wasted, God gets quite
irate. Please make sure you try to use one of the latter forms and not the
first form, and make a happy deity. 🙂