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Tips for lxplus

Folder permission on lxplus

This is needed to grant collogues access to certain files stored on lxplus.

AFS

AFS (mostly) ignores UNIX permissions1. Instead, use fs setacl to control access right: 

fs setacl <path_to_folder_on_afs> system:anyuser read

To check current access permissions of a folder: 

fs listacl <path_to_folder_on_afs>

Warning

Only new subdirectories inherit the parent directory's permissions.

For more info, consult this link1.

EOS

It is unclear on how to share files stored in EOS as naive chmod won't work and sharing via web interface won't work.

VNC to lxplus

First, run the VNC server on a lxplus node: 

vncserver :8 -localhost -name Lxplus-Session -geometry 1024x768

If it is your first time running vncserver, it may prompt you to set a remote-access password.

Unfortunately, the default ~/.vnc/xstartup doesn't work out of box. You can confirm that by trying to kill the newly-launched server: 

vncserver -kill :8
and you may get something like this: 
Can't find file /afs/cern.ch/user/s/suny/.vnc/lxplus732.cern.ch:8.pid
You'll have to kill the Xvnc process manually

Now, we need to configure a working desktop for VNC. Clear your ~/.vnc/xstartup and copy the following lines1 to that file:

#!/bin/sh

unset SESSION_MANAGER
unset DBUS_SESSION_BUS_ADDRESS
icewm &

Re-launch the vncserver on lxplus with the same command. If the port :8 is taken by someone else, use a different port. Remember the lxplus hostname (denote as lxplus_host) and port number (denote as port).

Now we need to map the VNC port to a localhost port, likely due to firewall issues: 

ssh -L <port>:localhost:<port> <user>@<lxplus_host>.cern.ch

Note

Here port must be in full number. e.g. :8 -> 5908.

Finally, we can access our remote lxplus desktop with: 

vncviewer <port>

  1. Courtesy of Will. ↩↩↩