NFS version 4

Support for NFS version 4 has now been enabled on the main NetApp filer “elmer”. The change is upwards compatible in the sense that the older protocol remains available as well. However client systems which support multiple versions will normally use the highest version available from a server, so many machines will see a change.

There are many internal differences between version 3 and version 4, some of which may lead to improved performance.

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WGB power cut 2014/11/09 17:43

There was a power cut in the WGB just before 17:43 for about ten seconds. See UIS report for their timeline.

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internal ‘sysdata’ web service fist to move to NFS sec=sys is the first of the Lab web services to move to Ubuntu servers running Apache 2.4 using NFS sec=krb5 to access the web pages from the filer. Please contact sys-admin if there are any problems. Other services are likely to move over in the near future.

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Matlab updated to R2014b

The version of Matlab used on lab Linux systems has been updated from R2013b to R2014b.

Condor users should be aware that the pathname of the version of Matlab that they should use under condor has also changed, see


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Removal of avahi-daemon from Ubuntu 14.04 systems

It appears that the avahi-daemon causes the gtk+ library on Ubuntu 14.04 systems used by many GUIs  (e.g. firefox and chrome) to hammer the print spooler by opening hundreds of simultaneous connections, causing the GUI to crash. To avoid this, we are removing the avahi-daemon on all Ubuntu 14.04 systems. If you manage a machine which needs it, simply add ‘avahi-daemon’ to /etc/user-config/bundles as usual. and it will be auto-installed.

In lots more detail: About a year ago we updated our CUPS print server to a version which supported Bonjour/Avahi export of printer information. This was mainly to make life easier for Mac/Windows users, Linux users continued as before as Linux systems hadn’t added Avahi support at that time. Avahi support was added in Ubuntu 13 through the gtk+ v3 library. From that point on we started seeing problems as it turned out that Avahi printer discovery told gtk+ about our printers several times over. So applications using gtk+ (such as evince/Document Viewer, browsers etc) were frequently polling the CUPS server about each printer discovered by Avahi, resulting in several hundred simultaneous connections from the application to the CUPS server. Not surprisingly the CUPS server ground to a halt for about 15 mins whenever anybody using a Ubuntu 13/14 system tried to print. This caused a problem for everyone in the Lab, not just Ubuntu 13/14 users. As we hadn’t discovered the cause at that point we had no choice but to implement throttling on the CUPS server so that it would only accept up to 50 simultaneous connections from any one host. This prevented the CUPS server from dying, at the expense of printing problems for the (at that time small number of) Ubuntu 13/14 users – if using a printer at the top of the list printing would succeed but be quite slow, if using a printer at the bottom of the list then your application would probably crash. Our only solution was to suggest applications that don’t use gtk+, such as okular which is a PDF viewer superior in every way to evince/Document Viewer, and which we still recommend. We haven’t discovered a way to “fix” Avahi, but we have now discovered that removing the Avahi daemon altogether solves the problem completely – gtk+ backs off to a less harmful means of printer discovery, and applications don’t notice. We are not aware of any other use for Avahi on our systems, so we are simply removing it.

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Internal Lab facilities may not be available

Certain commands used to do “privileged” things within the Lab may not be working for a while. If some feature you particularly need does not work, please email details to sys-admin

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condor pool moved to NFS sec=krb5

As emailed to all recent users of condor, the execute machines have now moved to NFS sec-krb5. The documentation has been updated. If anyone has problems, please email sys-admin.

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Lab PhD wins Ubicomp 2014 Best Paper Award

Chloe Brown has received the Best Paper Award at the 2014 ACM International Joint Conference on Pervasive and Ubiquitous Computing (Ubicomp 2014).

The paper “The architecture of innovation: Tracking face-to-face interactions with ubicomp technologies” is joint work with Christos Efstratiou, Ilias Leontiadis, Daniele Quercia, Cecilia Mascolo, James Scott and Peter Key

Chloe Brown is a member of the Network and Operating Systems group under the supervision of Professor Cecilia Mascolo.

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September edition of ‘The Ring’ now online

The September edition of ‘The Ring‘ is now available.

Please contact for more information on the Computer Laboratory’s graduate association.

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network and Xen problems

A misconfiguration in the networking kit caused an outage yesterday afternoon. This caused many Linux Xen VMs to loose access to their root filesystems, so they mounted them read-only. After rebooting some of them, one of the Xen Servers lost the ability to reboot VMs, so itself had to be rebooted, causing all its VMs to crash. Many of the filesystems were deemed “unfixable” by fsck, so fsck had to be manually run before the systems rebooted.
Please let sys-admin know of any remaining problems.

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