Setup Complete

Setting up using pure git

Set up a development environment.

Prerequisites for building LHCb software

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

Before building, there are a few recommended customisations to prepare in your environment, besides those discussed in the previous lesson.

Ninja (optional, faster replacement for make)Click to expand

If you have ninja in your path, it will be used to (marginally) speed up the make process, and it is automatic; you still use make ... commands. To add it:

local:~ $ export PATH=/cvmfs/lhcb.cern.ch/lib/contrib/ninja/1.4.0/x86_64-slc6:$PATH

You can also add:

local:~ $ export VERBOSE=

if you are a fan of reduced noise when building.

CCache (optional, faster rebuilds)Click to expand

If you rebuild often, you should be using CCache. This program stores the results of compiling and reuses them if nothing changes. You should be able to do something like this after you install CCache:

local:~ $ export CCACHE_DIR=$HOME/.ccache
local:~ $ export CMAKEFLAGS=-DCMAKE_USE_CCACHE=ON

If you installed CCache from source locally to $HOME/.local, then you'll need the local bin in your path, too:

local:~ $ export PATH=$HOME/.local/bin:$PATH

Debug buildsClick to expand

If you want a debug build, you'll need to change some environment variables with the LbLogin program, which will start a new bash instance with the required variables using the configuration name in $CMTDEB:

local:~ $ LbLogin -c $CMTDEB

Path

You should have a main development directory, and it should be in your CMTPROJECTPATH variable. If you use $HOME/lhcbdev, then you would do:

local:~ $ export CMTPROJECTPATH=$HOME/lhcbdev:$CMTPROJECTPATH

In VMs and Docker, sometimes the root directory /workspace is used.

Git for LHCb

You can set up a development environment with complete LHCb packages, and build them from scratch. This allows you to make large scale changes without locating sub-packages online, and is similar to the standard procedures in other projects. The downside to this is that they take a while to compile, due to the size of LHCb projects. Since the following is very similar to standard git procedures, most online git tutorials are also helpful in understanding the meaning of the various git command used.

Help for the git noviceClick to expand

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

local:~ $ 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

local:~ $ 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 problemsClick to expand

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.

Setting up the projects

To get a complete project for development, the following command will work:

local:~ $ git clone ssh://git@gitlab.cern.ch:7999/lhcb/Project.git

where Project is the name of the project. The location of this project on your computer is important! It should have the following structure:

Main LHCb folder (any name, like $HOME/lhcbdev)
- Project (git folder here)
- AnotherProject

The package structure is this way to allow the package search system to find names and versions. The main folder should be listed in the $CMTPROJECTPATH environment variable.

Once you have cloned the repository, you should check out the branch that you want to build/work on with git checkout -b BranchName.

An complete example for the Lbcom package would look like this, using a destination for the git folder, since it will default to the wrong name:

local:~ $ mkdir ~/lhcbdev
local:~ $ cd ~/lhcbdev
local:lhcbdev $ git clone ssh://git@gitlab.cern.ch:7999/lhcb/LHCb.git
local:lhcbdev $ cd LHCb
local:LHCb $ git checkout -b upgradeTracking

Inside the project, the CMakeLists.txt file may reference other projects, like this:

gaudi_project(Project LocalVersion
              USE ReferredToProject RemoteVersion
              DATA OtherStuff)

You need to set the LocalVersion to your version (such as upgradeTracking), and you need to set any dependencies to the version names you've set, as well. When gaudi_project looks for a package, it will look for ones that follow the above naming scheme and have the correct, matching version.

Note: You do not need to locally build all dependencies if there is a released version that will work; they will be found if you do not have a local version.

Building

To build, you need to run the following commands in each package directory (starting with dependencies first):

local:LHCb $ lb-project-init

This will setup the makefile, and some other things. Then run:

local:LHCb $ make configure

to configure the run (it runs CMake behind the scenes). If this fails, you probably have a problem in your CMakeLists.txt or with your paths.

To build and move the results to the folder that CMT expects, run:

local:LHCb $ make install

This should take a long time the first time, and should be much faster after that.

Future reading

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

Pure git