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Working with LHCb Software and SLC6

SLC6 on

On the 6th of May, the CERN IT Department will change the alias to point to the new cluster, installed with Scientific Linux CERN, version 6. More information on this change can be found at:

Warning, important This is only a change of alias, the previous linux cluster will still be available under the name "".

Compiling and Running jobs on SLC6

Whereas running SLC5 binaries on SLC6 is straightforward, and has been done for a while in production, the opposite is more difficult and can only be with the gcc46 configurations.

Now that SLC6 is the default on lxplus (and many office desktops), while most of the grid nodes are still using SLC5, please be aware of the following points:

When logging to an SLC6 machine, the default CMT configuration is "x86_64-slc6-gcc46-opt".

This configuration is supported by a large part of the LHCb Software stack (work is being done to release the rest of the stack). It is possible to compile/run your algorithm with this configuration, but most of the grid resources have not been migrated to SLC6 yet.

Jobs with configuration "x86_64-slc6-gcc46-opt" should not be submitted to the grid

slc6-gcc46 jobs should not be submitted the grid at the moment, as all Tier 1 sites are not equipped with SLC6 queues yet. Sites are currently migrating their computing resources to SLC6 (or compatible), we will send more information when available.

Warning, important Trying to submit your ganga jobs with this configuration will result in an error.

It is still possible to use Ganga from an SLC6 node, but in that case it is necessary to set your environment as being SLC5 for cross-compilation and job submission (see next point)

SLC5 cross-compilation on SLC6

You can continue to work with the "x86_64-slc5-gcc46-opt"configuration that was the default on SLC5. In order to do so you need to call:

LbLogin -c x86_64-slc5-gcc46-opt
SetupProject DaVinci


LbLogin -c x86_64-slc5-gcc46-dbg
SetupProject DaVinci

Warning, important Please note that just changing the CMTCONFIG environment variable is not sufficient as you need to invoke the LbLogin command in order to set your environment to a specific compiler.

Warning, important LbLogin for x86_64-slc5-gcc46-opt (or dbg) sets the CMTUSERCONTEXT environment variable, used by CMT. This is necessary in order to use the gcc 4.6.2p1 compiler from the LCG externals, that allows for cross compilation (whereas the default 4.6.2 will generate incompatible binaries). If you are using the CMTUSERCONTEXT environment variable yourself, you need to include the following lines in your User context requirements file:

macro gcc_config_version '$(gcc_config_version)' \
       target-slc5&host-slc6&target-gcc46 '4.6.2p1'

Using the gcc43 compiler

To use the gcc43 compiler (e.g. for versions of Gauss prior to v45...) you need to connect to a SLC5 host such as as the cross compilation of gcc43 code on SLC6 does not work. This is also true for 32 bit configurations.

In case of problems

In case of issues potentially related to this, the best is to try and submit the jobs from to see if it makes a difference and to contact the core software team if it is the case.

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Topic revision: r5 - 2013-04-29 - BenjaminCouturier
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