AFS at Glasgow

AFS ACLs (Protecting Data)

AFS file systems use directory based ACLs to determine the access permissions for a given file. The following is taken from the afs documentation (http://docs.openafs.org/AdminGuide/ch15s02.html):

• The permissions on a directory's ACL apply to all of the files in the directory. When you move a file to a different directory, you effectively change the access permissions that apply to it to those on its new directory's ACL. Changing a directory's ACL changes the protection on all the files in it.
• When you create a subdirectory, its initial ACL is created as a copy of its parent directory's ACL. You can then change the subdirectory's ACL independently. However, the parent directory's ACL continues to control access to the subdirectory in the following way: the parent directory's ACL must grant the l (lookup) permission to a user (or a group the user belongs to) in order for the user to access the subdirectory at all.

By default the following directories are created in a user's afs home area:

• private - access only for the user and the system administrator, this is also the default for any new directories.
• public - public (world wide) access for anyone.
• public_html - public (world wide) access for anyone, user web pages belong here.
• public_ppe - readable to the ppe group only.

To see the acl list on a directory use the command fs listacl dir .

To allow a user or group user read access to a directory dir :

fs setacl dir user read

To give write permissions:

fs setacl dir user write

And to remove all permissions for a user or group:

fs setacl dir user none

Recursive setting of ACLs

A helper script to recursively set an ACL is available on all the scientific linux desktop machines. Usage is similar to the standard fs setacl command:

fs-recursive-setacl dir user acl

Accessing the CERN afs cell (/afs/cern.ch)

Getting a kerberos ticket for another kerberos realm using kinit will overwrite the existing kerberos tickets file destroying any local Glasgow ticket. To get around this tickets for different kerberos realms have to be written to different files. A couple of helper scripts have been written to made this straight forward: kinit-cern, klist-cern, kdestroy-cern, ssh-cern, kinit-fnal, klist-fnal, kdestroy-fnal, ssh-fnal.

They are used in the same way as the standard kinit, klist and kdestroy. For example:

$ kinit-cern <lxplus user name>@CERN.CH

and after doing the kinit:

$ ssh-cern <lxplus user name>@lxplus.cern.ch

rsyncing files to afs

drwxrwsr-x  4 ppemgr ppemgr   45 Jan 14  2009 sl44

chmod a-s _dir_

Automatic Token Renewal

ssh login

For csh/tcsh users the untested equivalent is to add the following to the top of .cshrc or .tcshrc:

if ( -e /bin/ps && -e /bin/grep ) then
    setenv kproc `/bin/ps x -u ${USER} | /bin/grep krenew | /bin/grep ${KRB5CCNAME}`
    if ( "${kproc}" == "" && -e /usr/bin/krenew ) then
        /usr/bin/krenew -K 60 -t -k ${KRB5CCNAME} &
    endif
endif