Bazaar for subversion users, part 1 – the basics

Table of contents

Introduction to the seriesBACK TO TOC

This series of articles continues a subject that I started in one of my previous posts. Due to reasons I’ll describe in a second, Subversion doesn’t work for me anymore. I have a bunch of one developer projects that I would like to manage. My version control server (Subversion server at the moment) is on the Internet, works over HTTP. Because of that, it is slow. So slow, that it made me crying for a new version control.

Working with Subversion is still fun. If you’re working in an environment where all project participants are close to each other, then it is still my VCS of choice. This is because Subversion is a mature VCS with great community supporting it – this translates into excellent clients for various OSs, great support, etc.

Yet today more and more projects operate in a distributed manner. This is especially true for open source projects, where project participants often live in various countries. This is also true for people like me – those who prefer to keep their repository online from high availability considerations.

This series of articles is a summary of things that I had to learn to know Bazaar and to convert some of my projects from Subversion.

Introduction to the articleBACK TO TOC

This is the first out of several articles that I plan to conduct on the subject. In this article we will see the basics. Material I present here is introductory. It should be enough to get you started and as you will advance more articles will arrive.

Way of working with BazaarBACK TO TOC

There are to ways of working with Bazaar.

  • Purely distributed
  • Semi-centralized

First means that there’s no central repository. Every user works in his own repository and repositories can be easily merged. Moreover, the entire concept of branch and repository has been put together. Meaning that there are no repositories per se anymore. Each branch is a repository and a repository is a branch.

Semi-centralized approach means that repositories kept on remote computer and we checkout the repository – just like in Subversion.

The major difference between the two is that in the first case we checkout a repository that sits on our computer, usually in the same directory as the repository (more on this later in the series). In the later case, we have to checkout the remote repository.

This article intended for Subversion users and because of that I will concentrate on a second approach. Despite that, once you’ll understand the concepts behind all this, you will be able to work both ways.

Demo setup descriptionBACK TO TOC

For the sake of the demonstration, I prepared two Ubuntu Jaunty (that is Ubuntu 9.04) computers. First named hubuntu. This is our server computer – this is where I’ll keep the main repository. Second computer called shmubuntu. This is the client computer.

Directory and user configurationBACK TO TOC

Repository files on hubuntu, the server computer should have dedicated place and an owner user. For that reason I created a user named bzr. Then I created directory /srv/bzr and chown‘d the directory to the user. Finally, I created two more directories: /srv/bzr/trunk and /srv/bzr/branches. trunk directory is for the main repository. branches directory is for branches. This is exactly like it is in Subversion.

Then, I installed Bazaar on both computers. In case you’re wondering, on Ubuntu, you can do it with:

alex@hubuntu:~$ sudo aptitude install bzr

Next, I created two users user1 and user2 on shmubuntu. These are the users that will do the job.

Finally, I installed user1‘s and user2‘s identity on bzr@hubuntu. I did it because bzr on hubuntu owns the repository. We want user1 and user2 to be able to modify the repository files. To do that we should either add user1 and user2 on hubuntu and configure permissions or to make sure that user1 and user2 work on hubuntu as bzr, the user that owns the repository. The later seems to be much easier to do.

The basicsBACK TO TOC

Creating a projectBACK TO TOC

It all starts with creating a project. Lets say our user1 logged into shmubuntu wants to create a new project and place the repository for the project on hubuntu. Here is what user1 should do.

user1@shmubuntu:~$ bzr init sftp://bzr@hubuntu/srv/bzr/trunk/project1

There are couple of interesting things about this command. First of all, init creates a new repository. What you should specify is a directory where you want it. By the way, directory should not exist. If it exists, Bazaar will complain about it. Otherwise, it will create the directory automatically for you.

If we want to work in a truly distributed manner, we create the repository in a local directory. But since we work in a centralized manner, we create the repository on a remote computer.

When creating local repository, the directory name should be plain Unix path. For remote it should be standard URI. The protocol in the URI can be either sftp for scp like protocol, or ftp. Other commands also accept http as a protocol, but in Bazaar it is read-only protocol. Since we actually want to write something to the repository, http won’t work for us.

Finally, note that we’ve created a repository named project1 under trunk directory. If you go to that directory on the server, the only thing you’ll find there is a directory named .bzr. This is where Bazaar keeps its meta-data. Unlike Subversion that keeps .svn in every directory under the project, Bazaar has its .bzr only under root directory of the project. This way it stands less in your way when, for instance, packaging the project.

Checking-out the projectBACK TO TOC

Check-out is plain and simple.

user1@shmubuntu:~$ cd works/
user1@shmubuntu:~/works$ ls
user1@shmubuntu:~/works$ bzr co sftp://bzr@hubuntu/srv/bzr/trunk/project1
user1@shmubuntu:~/works$ ls
project1/
user1@shmubuntu:~/works$

As you can see, its just like in Subversion. There are couple of things to notice here:

  1. Note that I checked-out the project as user bzr on server’s side. This is because this is the user that has write permissions on repository files and we will need write it when we will commit.
  2. Bazaar creates the project directory for us, just like it did when we created the project.

Note that co is an alias to checkout. So, the command could be bzr checkout.

Adding files to the projectBACK TO TOC

This one is also exactly like in Subversion. For the sake of the demonstration I created a small C project, with one source file and a small library in a separate directory. All compiled with single Makefile.

user1@shmubuntu:~/works$ cd project1/
user1@shmubuntu:~/works/project1$ ls
Makefile  main.c  some/
user1@shmubuntu:~/works/project1$ bzr add
adding Makefile
adding main.c
adding some
adding some/some.c
adding some/some.h
user1@shmubuntu:~/works/project1$

Like in Subversion, this doesn’t mean the files are in repository. To actually add the files into repository we’ll have to commit them.

Committing filesBACK TO TOC

This is also, exactly like in Subversion.

user1@shmubuntu:~/works/project1$ bzr ci -m 'initial commit - added project files'
Committing to: sftp://bzr@hubuntu/srv/bzr/trunk/project1/
added Makefile
added main.c
added some
added some/some.c
added some/some.h
Committed revision 1.
user1@shmubuntu:~/works/project1$

ci is an alias to commit. -m command line switch tells Bazaar to append a message to the commit. Without -m, Bazaar will open default editor asking you to write a message in the editor.

Few words about revision numbers in BazaarBACK TO TOC

In Bazaar each repository has a current revision number. Each time you commit, the revision number moves forward by one. You can identify state of your revision by its revision number. This means that like in Subversion, you can checkout certain version of the project using revision number. Branch revision numbers are different. We’ll talk about this later in the series.

Local commits or offline commitsBACK TO TOC

We’ve already seen how to commit directly into repository, but how this solves the performance issue with the centralized VCS ? After all, if all Bazaar is able to do is to commit into a repository on remote host, how is it faster then Subversion for that matter?

The point is that Bazaar allows you do so called local commits. We’ll talk about this in greater detail in the next part of this series of articles. In the meantime, I would like to introduce you to the topic.

As unusual as it might be, there is almost no difference between your local, checked-out, copy of the project and the remote repository. I.e. what you have on your hard drive after checking out the project, is the entire repository. Actually, you can let other people to check-out your copy of the project.

As a matter of fact, the term repository does not exist in Bazaar. Instead of repositories there are branches. Checked-out branch or a checkout is just a branch of a special kind. What’s important to understand now is that you can actually commit into Bazaar’s checkout, without committing to original branch that we’ve checked out.

To do a local commit, append –local command line switch to the commit command. Like this:

user1@shmubuntu:~/works/project1$ bzr ci --local -m 'did another change'
Committing to: /home/user1/works/project1/
modified main.c
Committed revision 6.
user1@shmubuntu:~/works/project1$

This command will not transmit a thing over the net. Instead it will save all the changes locally.

Committing local commits to remote branchBACK TO TOC

At some point in time, we will probably want to commit our local commits into the main branch. Unfortunately, Bazaar won’t let us do it straightforwardly. Instead it will ask us to update first. This is a little annoying as there’s no obvious reason for this – actually there’s an open bug on this in Bazaar’s launchpad page. Anyway, here is what we have to do:

user1@shmubuntu:~/works/project1$ bzr update
 M  main.c
All changes applied successfully.
 M  main.c
All changes applied successfully.
Updated to revision 6.
Your local commits will now show as pending merges with 'bzr status', and can be committed with 'bzr commit'.
user1@shmubuntu:~/works/project1$

And then:

user1@shmubuntu:~/works/project1$ bzr ci -m "June 30'th 2009 daily commit"
Committing to: sftp://bzr@hubuntu/srv/bzr/trunk/project1/                                                                                   
modified main.c
Committed revision 7.                                                                                                                       
user1@shmubuntu:~/works/project1$

Note the comment I’ve left on the commit. This is actually a cool idea – that is to do all commits locally and do daily commit to main repository using cron task. This way we can do commits fast, without waiting for slow internet.

Multi-user environmentBACK TO TOC

Making modifications to files and viewing differencesBACK TO TOC

Committing non-up-to-date fileBACK TO TOC

Now it is time to engage user2. Lets say that user2 has changed one of the project files and committed it – file named main.c in our case. user1 has changed that file too and now wants to commit his change. So, first we have:

user2@shmubuntu:~/works/project1$ bzr ci -m 'added include to string.h'
Committing to: sftp://bzr@hubuntu/srv/bzr/trunk/project1/
modified main.c
Committed revision 3.
user2@shmubuntu:~/works/project1$

And then we have:

user1@shmubuntu:~/works/project1$ bzr ci -m 'a couple of minor changes'
bzr: ERROR: Bound branch BzrBranch6('file:///home/user1/works/project1/') is out of date with master branch BzrBranch6('sftp://bzr@hubuntu/srv/bzr/trunk/project1/').
To commit to master branch, run update and then commit.
You can also pass --local to commit to continue working disconnected.
user1@shmubuntu:~/works/project1$

Here, Bazaar behaves exactly like Subversion. As you remember, Subversion won’t let your commit to overwrite a file that has been changed in repository. I.e. if repository contains newer version of the file, Subversion will ask you to update first. This is exactly what Bazaar has asked us to do.

Merging with the latest version of the fileBACK TO TOC

Since our user1 ran into a conflict, he has to update his local repository first. We already saw this command in action:

user1@shmubuntu:~/works/project1$ bzr update
M  main.c
All changes applied successfully.
Updated to revision 3.
user1@shmubuntu:~/works/project1$

Note that update will overwrite user1′s changes. On the contrary, Bazaar will try to merge the changes. If it succeeds, like it did in our example, then you’ll have to commit the file. Like this:

user1@shmubuntu:~/works/project1$ bzr ci -m 'a couple of minor changes'
Committing to: sftp://bzr@hubuntu/srv/bzr/trunk/project1/
modified main.c
Committed revision 4.
user1@shmubuntu:~/works/project1$

Here, Bazaar again behaves exactly like Subversion. It does update the file as long as this update doesn’t break anything. But what if there’s a conflict? This, and many other things you will find in the second part of this article series, which comes in a couple of days. Stay tuned.

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One Comment

  1. Destillat KW27 | duetsch.info says:

    [...] Bazaar for subversion users, part 1 – the basics [...]

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