EOS is the disk storage system at CERN for large physics data.

Important: all EOS files are disk-only (no backup) In case of inadvertent deletion by users or a major hardware failure EOS files cannot be recovered


Latest instructions on EOS/CERNBox:




You should have the following variable set as:

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

-> all the commands like "eos cp,..." should then work

To mount:

export EOS_MGM_URL=root://eoscms.cern.ch//eos/totem/ eos fuse mount ~/MyEos

Some of the instruction below are not valid anymore


% source /afs/cern.ch/project/eos/installation/totem/etc/setup.sh

EOS home directories have a similar structure to your AFS directory. The detailed structure of the EOS repository in TOTEM is:

/eos/totem/user/x/xyz /eos/totem/data

  • create a subdirectory in your /user/x/xyz directory:

% eos mkdir /eos/totem/user/x/xyz/mysubdir

  • copy a local file to your EOS directory

1) XROOT protocol:

% xrdcopy test.txt root://eostotem/eos/totem/user/x/xyz/eos.txt

=> download from EOS

% xrdcopy root://eostotem/eos/totem/user/x/xyz/eos.txt eos.txt


# copy a single file

% eos cp /eos/totem/user/x/xyz/histo.root /tmp/

# copy recursive the complete hierarchy in a directory

% eos cp -r /eos/totem/user/x/xyz/histodirectory/ /afs/cern.ch/user/x/xyz/histodirectory

# copy recursive the complete hierarchy of a CASTOR directory to an EOS directory (make sure you have the proper CASTOR settings)

% eos cp -r root://castorpublic//castor/cern.ch/user/x/xyz/histordirectory/ /eos/totem/user/x/xyz/histodirectory/

  • Mounting EOS on lxplus

You can mount EOS into your AFS home directory as follows:

% mkdir -p $HOME/eos

% eosmount $HOME/eos

Please unmount it once you are over or before you log out !!! (NEVER NEVER rm the /eos directory before unmounting it!). Remember also about not mounting EOS in temporary directories! After logging out, /eos in temporary directory will be erased!

% eosumount $HOME/eos

or if you have some hanging mount

% eosforceumount $HOME/eos

Warning: after 24h the mount has to re-authenticate and your kerberos token will have expired in the meanwhile. So whenever you login into lxplus re-fresh (=eosumount + eosmount) any existing mount (even better don't let it there).

Disclaimer: the FUSE module is not recommended for production usage and the use is at your own risk. EOS is not mounted/mountable on lxbatch nodes!

  • Protections

Despite the building of the path of the files suggests a tree structure fo the filesystem, EOS is NOT a filesystem. Each file is treated individually. Which means that any user can delete any file which is stored in a non protected directory. In Totem each user can delete only its own files. But it can happen that accidentally a user from another group can remove files IF YOUR DIRECTORY is not protected. EOS permission system is based on a combination of POSIX and ACLs permissions. By default the user directories are created rwx-r----- (750) and you can check the ACL settings via

%eos attr ls /eos/totem/user/x/xyz sys.acl="egroup:totem-eos-admin:rxcm,g:zj:!d,g:zh:!d"

PLEASE Don't change the permissions, or if you do temporarly remember to restore back the original.

  • Quota

EOS has a quota and you can check it with the command "_eos quota_". Please note that you have a limit on size and on number of files.

The 'eos' CLI supports most of the standard filesystem commands like ls, cd, mkdir, rm, rmdir, find, cp ... [ 'eos help' shows all available commands, 'eos --help' explains each command ]

Accessing an EOS file from ROOT:

root [0]: TFile::Open("root://eostotem.cern.ch//eos/totem/user/x/xyz/histo.root");

More info:



-- ValentinaAvati - 25 Feb 2014

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Topic revision: r8 - 2021-04-08 - ValentinaAvati
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