DevelopKit

Setup Simple

Overview

Teaching: 10 min
Exercises: 10 min
Questions

  • Can you set up an incremental build?

Objectives

  • Prepare a package and check out a portion of it.

Prerequisites for building LHCb software

You should have a valid LHCb environment, using one of the ways previously mentioned, or by working on lxplus. You may need to run source /cvmfs/lhcb.cern.ch/group_login.sh to set up your environment variables.

Git

LHCb uses the git versioning system.

Prerequisites for git

Before using git, you should go to your gitlab.cern.ch account and set up an ssh key. The procedure is the same as with github (and the public key is the same). In short, on Linux or Mac, make sure you have key pair in ~/.ssh/id_rsa.pub and ~/.ssh/id_rsa. If you don’t have one, run

ssh-keygen

and use the default location. If you don’t put in a passphrase, you can directly push and pull without a password; if you do put a passphrase, you can run

test -z "$SSH_AGENT_PID" && eval $(ssh-agent)
ssh-add

when you start a terminal to enter your passphrase once per session. Your computer keychain (Mac, Ubuntu, etc) can also store your password once per login.

If you encounter problems

If you get an error about your ssh agent not running, you can execute the output of the ssh-agent command with eval $(ssh-agent) and try again.

Once you verify you have an ssh key pair, you need to go to the gitlab website, go to your profile (possibly hidden behind the hamburger button), then edit, then SSH Keys (or just go here), and paste the contents of the id_rsa.pub file into the key edit box. You can give it a title that allows you to identify the computer or VM associated with the key.

Defaults

You can set the lb-commands to default to ssh by running the following line to save a global (all repository) config variable:

git config --global lb-use.protocol ssh

You can also set the git default push policy for git if you have a version between 1.7.11 and 2.0:

git config --global push.default simple

This is not mandatory, but is a more reasonable default (and is the default in git 2.0. Note that SLC6 systems, like lxplus, have a version less than 1.7.11. On these systems, you can still set the default to current, which is better than the original default of matching.

Aside: Explanation of defaults for the curious

This aside is will only make sense if you know a little bit about git. If you are working on a branch local_branch and you push without explicitly telling git what to do, it will do the following:

Coming from SVN?

If you have a background with SVN, you might want to look at the two part tutorial from IBM for subversion users, Part 1 and Part 2.

LHCb simplifications

While vanilla git commands are covered in the alternate lesson, this lesson uses special LHCb commands added to git. These are special programs that sit in the LHCb bin, and have names that start with git-. Git automatically converts a command like git x to git-x, so these seamlessly blend with the built in commands. To differentiate them, they all start with lb-.

Setting up a satellite project

If you want to setup a satellite project (local project) for small changes, you’ll need to prepare that project:

lb-dev Project vXrY
cd ProjectDev_vXrY

For example, the project might be DaVinci, and the version might be v40r3p1. Then, you’ll been to tell git where it can checkout subprojects from:

git lb-use Project

This sets up a remote that points to the LHCb repository Project on GitLab.

To get the code from Project/Branch to checkout into Some/Package:

git lb-checkout Project/Branch Some/Package

The branch can be master, or a specific version vXrY, or any other valid branch. See the GitLab page to browse projects and branches.

Future reading

The twiki page Git4LHCb is currently the best source for git examples.

Key Points