Access to CERN EOS from BNL¶

The ways to list, write and read files on CERN EOS, documented here, still work at BNL, but you need specify the full EOS server name eosatlas.cern.ch and obtain a CERN Kerberos ticket.

You can obtain and cache a CERN Kerberos ticket (this is also required for the way of using ssh-tunnel below) by:

kinit YourNameAtCERN@CERN.CH

CERN.CH must be uppercase

Please be aware that in the above command the realm CERN.CH must be in UPPERCASE.

As convenience for the US ATLAS users, we have installed the eos-client and eos-fusex packages on the interactive nodes.

After obtaining your CERN Kerberos ticket, you can access both the ATLAS EOS and USER EOS instances.

To list your files:

ls /eos/atlas/...
ls /eos/user/y/yesw/...

Note

Please replace "y/yesw" with your own username at CERN.

To copy files from EOS:

cp /eos/atlas/YourDir/YourFilename.root .

To copy files to your EOS area at CERN:

cp MyNewFile.xxx /eos/atlas/YourDir/MyNewFile.xxx

You can create new directories in your EOS area at CERN:

mkdir /eos/atlas/YourDir/NewDirectory

In addition, you can also use ssh-tunnel to eosatlas.cern.ch:

ssh -NfL 1094:eosatlas:1094 lxplus.cern.ch

Then you can list files on EOS:

xrdfs eosatlas.cern.ch ls /eos/atlas/..
xrdfs localhost ls /eos/atlas/..   # if using ssh-tunnel

To copy files from EOS:

xrdcp root://eosatlas.cern.ch//eos/atlas/YourDir/YourFilename.root .
xrdcp root://localhost//eos/atlas/YourDir/YourFilename.root .  # if using ssh-tunnel

Or you make use of the existing script eos-copy.py, which is an alias and should have been defined for you upon login:

% which eos-copy.py
/afs/usatlas.bnl.gov/scripts/eos-copy.py

% eos-copy.py -h
Usage: eos-copy.py [options] eos_source... local_dir
   eos-copy.py [options] eos_source... pnfs_dir

     widlcard such as "*.root" is allowed in the eos_source.

   This script uses xrdcp to copy files/dirs from CERN EOS to a local dir
or a BNL private dCache dir. A valid CERN AFS token is required.


Options:
  -h, --help  show this help message and exit
  --verbose   Print verbose info
  --version   Print the script version then exit

Or to read EOS files in ROOT:

TFile *file = TFile::Open("root://eosatlas.cern.ch//eos/atlas/YourDir/YourFilename.root");
TFile *file = TFile::Open("root://localhost//eos/atlas/YourDir/YourFilename.root");  // if using ssh-tun
nel

Access to CERN EOS in BNL batch jobs¶

The method using ssh-tunnel would not work in batch jobs, you need access them directly with root://eosatlas.cern.ch. However, for protected EOS files, you need pass your CERN Kerberos ticket to the batch machines in the following way:

First define one envvar KRB5CCNAME prior to running kinit YourNameAtCERN@CERN.CH:
```
export KRB5CCNAME=$HOME/krb5cc_`id -u`
```
Then add the envvar KRB5CCNAME to your condor batch jobs.

Access to CERN EOS through BNL Xcache server¶

If you need repeat access the same EOS files, you can make use of the BNL Xcache server to speed up the reading speed for the sequential access.

Just use the option --eos=EOS_PATH in the script Xcache_ls.py to generate the clist files for your EOS files at CERN. Please run Xcache_ls.py -h for more details.