Two Newsletter Articles

Sneaky preview of two draft articles to appear in this month’s DICE Newsletter: articles on SSHFS and FlexLM Licence Status.

SSHFS

This semester sees a majority of Informatics using AFS, the globally accessible filesystem which gives users direct access to their filesystem from a variety of operating systems and anywhere in the world.  However, AFS does not provide all the answers, and sometimes you need access to a data that isn’t or can’t be stored in your AFS file space, for example offsite or on a removable disk.  Shuffling files back and forth between devices is rarely convenient.  This is where SSHFS, the secure-shell remote filesystem, comes in.

SSHFS utilises FUSE (Filesystem in USErspace), a comparatively new addition to Linux and other kernels which allows users to mount filesystems in ways previously restricted to superusers.

Its function is relatively easy to guess, given the name.  It allows a user to mount any path on a remote host (to which they have access), given SSH access to that path.  It can be mounted on any local path on your DICE machine.

Let’s say you keep a large library of temporary files in scratch space on your DICE desktop.  You’d like to use this same cache on a remote server, but copying the whole directory would be inefficient since most of it remains unused.  Instead, you simply create a directory to act as a mount point, and mount your remote disk there:

[bigserver]me$ mkdir /tmp/largelib
[bigserver]me$ sshfs me@dicedesktop:/usr/local/largelibrary /tmp/largelib

That’s it.  Your files are accessible as if in /tmp; they’re accessible only to you and only on the DICE host which did the mounting.  When you’re done, you should unmount it like any other filesystem or medium.  In this case it’s a FUSE filesystem, u[n]mounted with the FUSERmount utility:

[dicepc]user$ fusermount -u /tmp/largelib

SSHFS makes no performance guarantees (consider the work it is doing to bring you your file…) and is not designed to replace local disk access for demanding tasks.  And don’t forget that your removable disks and remove storage does not necessarily come with the comprehensive backup mechanisms which protect your DICE home directory.

FlexLM Licence Status

A majority of the population are fortunate enough to have never heard of FlexLM, the self-proclaimed “flexible licence manager” utilised by several licensed software packages used in Informatics.  Many of those who have might consider its sole purpose to be to hamper efforts to run their favourite mathematical processing packages.

Several months ago the Research and Teaching unit refreshed the LCFG FlexLM component which manages all such software, attempting to make FlexLM less of an obstacle by allowing consistent management and tying in important improvements ranging from service monitoring to block licence reservation.  The new component runs on all DICE FlexLM servers and, though invisible to users, one feature – the licence usage page – should not be.

Each server now produces a regularly-updated summary of the licences, applications and features it provides, along with a list of checked-out licences and their users.  This is accessible by visiting:

http://licence-server:1881/

(that’s port 1881) from an Informatics PC.  Currently-licensed software includes Maple, Matlab and SIMICS, and users can contact support if they don’t know the name of their licence server.

One thought on “Two Newsletter Articles

  1. sxw

    One further consideration with anything that uses fuse is that it isn’t deadlock proof. Because of the way in which a user-space filesystem has to swap pages between kernel and user space, it’s possible that running fuse may deadlock the machine that it is running on.
    When that happens, it’s likely that there will be no option other than to reboot the machine.

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