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HowTo use EOS from the PSI Tier-3

Currently the local mounting of EOS has problems. But we can use the command line eos utility

For authentication EOS accepts either a kerberos ticket or your grid proxy. So, you have to either do a kinit using your CERN account name and password

$ kinit cern_username@CERN.CH

or you do a normal

voms-proxy-init -voms cms -voms cms:/cms/chcms

Available EOS endpoints

  • root://eoscms.cern.ch : the main CMS namespace where you e.g. find /eos/cms/store/mc and /eos/cms/store/user
  • root://eoshome-a.cern.ch, root://eoshome-b.cern.ch, ... : EOS home directory endpoints, one per username initial, where you can e.g. find root://eoshome-e.cern.ch//eos/user/e/exmpleuser

Define your endpoint in the EOS_MGM_URL environment variable or on the command line of the EOS client commands. Here are some examples of eos cubcommands (ls, cp). There are more, consult the eos manpage.

EOS client commands:

export EOS_MGM_URL=root://eoscms.cern.ch

eos ls -l /eos/cms/store/test/loadtest/source/T2_CH_CSCS/urandom.270MB.file0001
-rw-r--r--   2 phedex   zh          270000000 Feb 20 12:06 urandom.270MB.file0001

eos cp /eos/cms/store/test/loadtest/source/T2_CH_CSCS/urandom.270MB.file0001 /scratch/feichtinger/test
[eoscp] urandom.270MB.file0001   Total 257.49 MB        |====================| 100.00 % [97.8 MB/s]
[eos-cp] copied 1/1 files and 270.00 MB in 3.52 seconds with 76.62 MB/s

You can also use normal xrootd URLs to interact with the files from the command line or in your programs. This requires a grid proxy certificate for authentication (no kerberos). E.g. to interact with files in the home of my account dfeich, I can use:

  xrdfs eoshome-d.cern.ch ls /eos/user/d/dfeich/testfile-df
  # is equivalent to this
  eos root://eoshome-d.cern.ch ls /eos/user/d/dfeich/testfile-df

  xrdcp root://eoshome-d.cern.ch//eos/user/d/dfeich/testfile-df /scratch/feichtinger/mytest

EOS on local mounts - discontinued!

the local mounts are not working

We recommend using the EOS client tools and direct xrootd protocol tools above. The FUSE (userland) mounting of EOS may be convenient for local file management, but users tend to then also run massive code on the mounted filespace, while for those cases always the direct xrootd access should be used.

Currently CERN EOS is mounted on the User Interface machines t3ui01-03:

$ ls /eos

home-a  home-c  home-e  home-g  home-i  home-k  home-m  home-o  home-q  home-s  home-u  home-w  home-y  project
home-b  home-d  home-f  home-h  home-j  home-l  home-n  home-p  home-r  home-t  home-v  home-x  home-z  user

to get access to your EOS data, you first need to get a CERN kerberos ticket using the kinit command, which will ask you for your CERN password.

$ kinit cern_username@CERN.CH

Password for cern_username@CERN.CH:********** 

You will now have a kerberos ticket allowing access to CERN services. You can list the ticket and information about it using klist:


Ticket cache: FILE:/t3home/feichtinger/krb5cc_xyz
Default principal: dfeich@CERN.CH

Valid starting       Expires              Service principal
07.09.2023 17:50:39  08.09.2023 18:50:34  krbtgt/CERN.CH@CERN.CH
        renew until 14.09.2023 17:50:34

To mount EOS, you now just have to issue the following command

$ eosfusebind -g krb5 $HOME/krb5cc_$UID

Now you should be able to see your files by listing your EOS mounted dir, e.g. for me

ls /eos/home-d/dfeich

Please observe that EOS is not designed for high perfomance file access over the wide area network to CERN. You should not do intensive IO to EOS from the Tier-3.

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Topic revision: r8 - 2024-02-20 - DerekFeichtinger
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