(r7) LHCComputingGrid < CMS

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*Getting access to LHC Computing Grid.* One can find a brief introductory material at the [[http://www.grid.kfki.hu/?lcg&gettingstarted][RMKI's getting started page]], where you can find information on how to get access to LCG. There are also simple examples on that page.

*Some more practical information on running a typical job.*

   * Get authenticated on the LCG:

=> grid-proxy-init=        Here, you will be prompted for your grid password. Or:

=> grid-proxy-init -valid 4:00=        This is the same, but the authentication will be only valid for 4 hours.

Now you can perform various operations on the grid, e.g. send jobs. You can get info on your authentication (e.g. expiration etc.) by =grid-proxy-info=. You can destroy your authentication proxy by =grid-proxy-destroy=.

   * Get your jobs authenticated on the LCG:

=> myproxy-init=        Here, you will be prompted for your grid password, and to specify a password attached to your so called _job proxy_ to be created. Or:

=> myproxy-init -n=        Here, you won't be asked to specify a password for your proxy.

Running =myproxy-init= is necessary when you are running long-term jobs. In this case, the =myproxy-init= ensures that your jobs still will have authentication even after your interactive proxy (obtained by =grid-proxy-init=) has expired. You can get information on your job proxy by =myproxy-info=. You can destroy your job proxy by =myproxy-destroy=. Note: if you don't use this, you may not be able to retrieve your job outputs for long-term jobs!

   * Running a job:

A "Hello World!" example can be found at [[http://www.grid.kfki.hu/?lcg&gettingstarted][RMKI's getting started page]]. Instead of a "Hello World!" example, we present here a framework, with which one can send jobs in mass to the LCG: see the attached tarball called [[%ATTACHURL%/submit.tar.gz][submit.tar.gz]]. You can adjust these shell script wrappers to your needs. This assumes that your jobs are placed in a directory scheme like in the attached example [[%ATTACHURL%/skeleton.tar.gz][skeleton.tar.gz]]. This latter is a framework for simple jobs, which are ran on a simple computers (contains an automated Makefile and an automated starter shell script).

   * Specifying system requiremets:

It is a common task to require some software environment from the working nodes, where your jobs will be executed (e.g. AFS). You can specify requirements by placing lines like the following line to your .jdl file:

=Requirements = (Member("AFS", other.GlueHostApplicationSoftwareRunTimeEnvironment));=

One can apply logical operations to the arguments, like:

=Requirements = (Member("AFS", other.GlueHostApplicationSoftwareRunTimeEnvironment) && Member("VO-cms-ORCA_8_13_1", other.GlueHostApplicationSoftwareRunTimeEnvironment));=

   * Using the storage elements of the LCG:

The files are stored on Storage Elements on the LCG. Usually these have different physical file administration schemes. Therefore, a logical layer was built on top of them, which makes the file access uniform from the user point of view. To use this facility , use the environmental variable LCG_CATALOG_TYPE:

=export LCG_CATALOG_TYPE = lfc= (for _bash_), or 
=setenv LCG_CATALOG_TYPE lfc= (for _tcsh_).

The Logical File Name (_lfn_) is resolved by the Logical File Catalogue (_lfc_) server. You have to specify this:

=export LFC_HOST = lfc-cms-test.cern.ch= (for _bash_), or
=setenv LFC_HOST lfc-cms-test.cern.ch= (for _tcsh_).

Now you can refer to files with their logical file names, which are site-independent. The logical file names have to be unique. A very convenient way to generate them is to imitate the UNIX type file naming scheme. With the command =lfc-mkdir= one can make logical directories, like 

=> lfc-mkdir -m 755 /grid/cms/user_name/some_directory= (Here, the =-m xxx= option is optional, this sets the permissions of the directory. All logical file names begin with =/grid/virtual_organization=. If you are a new user, the directory =/grid/virtual_organization/user_name= will not exist initially: you have to create it first, if you want an own directory. It is recommended to restrict write permissions like in the example.)

There are various commands to manage logical file names, all beginning with =lfc-=, like =lfc-chmod=, =lfc-getacl=, =lfc-setacl=, =lfc-chown=, =lfc-ln=, =lfc-rename=, =lfc-ls=, =lfc-rm=, =lfc-mkdir= etc. Refer to the =man= pages of these commands, but the usage of these should be self-explanatory.

As the given logical directory is ready, one can copy files into it. If you want to store a file in the LCG storage infrastructure permanently, copying a file is not enough: you have to register the file in the logical file catalogue. It is done like:

<verbatim>
> lcg-cr --vo cms -d grid100.kfki.hu -l lfn:/grid/cms/alaszlo/destionation/testfile.txt \
                                                    file:/afs/kfki.hu/home/alaszlo/source/testfile.txt
</verbatim>
(Here, the =-d destination_Storage_Element= is optional, and is used to force the destination Storage Element to be =destination_Storage_Element=; otherwise the file may be copied to a Storage Element anywhere in the World.) This command will _copy and register your file_ onto LCG storage system. Once your file is there, you can get a copy of it with =lcg-cp= e.g. as an input for a job:

<verbatim>> lcg-cp --vo cms lfn:/grid/cms/alaszlo/some_directory/test_file.txt file:$PWD/test_file.txt</verbatim> (This command stages out the file in question onto a local --or AFS-- disc area, pointed at by =$PWD=, i.e. into your current directory.)

There are various commands to manage the stored files (e.g. unregister and delete them, or create replicas), all beginning with =lcg-=, like =lcg-rep=, =lcg-aa=, =lcg-rf=, =lcg-cp=, =lcg-cr=, =lcg-la=, =lcg-uf=, =lcg-del=, =lcg-lg=, =lcg-lr=, =lcg-gt=, =lcg-ra= etc. Refer to the =man= peges of these commands, but most of them are self-explanatory.

Unfortunately, one cannot copy and register complete directory trees. Therefore, I wrote a shell script wrapper to do this:

=> lcgcr.sh source_directory destination_directory_lfn= (You can find this here: [[%ATTACHURL%/lcgcr.sh][lcgcr.sh]].)

Note: unfortunately, I encountered that the =lcg-cr= action often fails (this should be remedied in future). Therefore, it is convenient to put an =lcg-cr= command into a checker loop:

<verbatim>
RESULT = 1
while (( $RESULT != 0 )) ; do
    lcg-cr --vo cms -d grid100.kfki.hu \
        -l lfn:/grid/cms/alaszlo/destintation/test_file.txt \
            file:/afs/kfki.hu/home/alaszlo/source/test_file.txt
    RESULT = $?
    if (( $RESULT != 0 )) ; then sleep 1m ; fi
done
</verbatim>

This precaution may also be recommended for =lcg-cp=.


-- Main.AndrasLaszlo - 06 Mar 2006

Attachments

Topic attachments
I	Attachment	History	Action	Size	Date	Who	Comment
sh	lcgcr.sh	r1	manage	3.8 K	2006-03-06 - 17:22	AndrasLaszlo	Copy and register complete directory trees into Logical File Catalogue
tar	skeleton.tar	r1	manage	30.0 K	2006-03-03 - 11:31	AndrasLaszlo	Framework for a simple job
gz	skeleton.tar.gz	r1	manage	4.0 K	2006-03-06 - 17:20	AndrasLaszlo	Framework for a simple job
tar	submit.tar	r1	manage	60.0 K	2006-03-03 - 11:32	AndrasLaszlo	A simple LCG mass submitter framework
gz	submit.tar.gz	r1	manage	7.6 K	2006-03-06 - 17:21	AndrasLaszlo	A simple LCG mass submitter framework

Topic revision: r7 - 2006-03-06 - AndrasLaszlo

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