[Live-demo] System behaviour in low disk space conditions

Jeremy Morley Jeremy.Morley at nottingham.ac.uk
Wed May 15 08:52:12 PDT 2013

Dear all,

While you're thinking about Live 7.0,some reflections from running version
6.0 from USBs with students this last semester. I know your main target is
DVDs but these may be of interest.

Firstly, it's pretty common when I'm working with students that they're
not careful with disk space but are used to having lots of it. Even if you
give them another partition on the USB stick, or even tell them about
accessing the hard drive on the machine from the Live system, inevitably
one or more will just download big ZIP files to their home directory,
unpack the contents there, never clear it out, etc. So eventually the home
directory & thus the system runs out of space. My observation is that the
system degrades very poorly in these circumstances, becoming unpredictably
unreliable and sometimes unbootable. Often it's PostgreSQL that seems to
be the poorest to cope but this is all anecdotal and hasn't been performed
in test conditions. Is there any way that this behaviour can be modified,
or at least some system monitor be included to warn of the impending
situation?  As a long-term user of computers & Linux/Unix-based systems I
can recognise the sort of system instability that arrises from
out-of-disk-space conditions so I know to go looking for it but the
students don't and it causes grief!

Secondly, the university runs a proxy to the Internet. The proxy setting
just in Xubuntu is fiddly enough (requiring updates to system files under
sudo in a number of places) and then there's the proxy settings in the
various packages. Even if it's not for this release, could there be a
long-term aim to provide a means at least to set the system proxy, and
better yet the package proxy settings? In part this is "my" problem as the
instructor in creating a tweaked version of the Live image to install on
our systems but actually if the students want to take the USB between the
uni and home (and thus out from behind the proxy) it gets fiddly for them
too. IIRC, plain Ubunutu has a settings panel that performs this task -
I've no idea about lubuntu etc.

A final issue is of ways to back-up from the system. I realise that a Live
system is not exactly intended for long-term use, and particularly not
from a USB drive. However I'd like to be able to use this with students
across a period of ~15 weeks. This year I found that the batch of USB
drives (Kingston DataTraveler 100 G2 16GB drives) did not perform well,
and 3-4 of them have failed (at a low level in the hardware, it seems, so
both partitions are lost & the devices are not recognised on the USB bus
as mass storage devices (or at all)). In some cases of partial failure
(e.g. when the booted system has filled and is not bootable) I can mount
the drive on another Linux system, mount the squash and casper files and
fish around to extract some of the contents, e.g. to copy to another drive
before re-imaging with a fresh Live installation. I'd just support the
requests to present an easy way to access the Live file system when the
stick is plugged into another system, or at least documentation on how to
mount the systems. I have, for example, yet to find where the PostgreSQL
contents are when accessing from a separate system. Alternatively, advice
on how to back-up the system would be very beneficial (maybe right up
front on the Live GIS Disc Quick Start for USB wiki page?).

I hope this helps. I realise the third topic is rather nebulous! Should I
enter any of the above as tickets? (They feel like higher level concerns
to me).


-- ------------------------------------------------------------ --
Jeremy Morley
Geospatial Science Theme Leader, Nottingham Geospatial Institute,
Triumph Road, University of Nottingham. NG7 2TU, United Kingdom.
Web:   http://www.nottingham.ac.uk/ngi     Twitter: jeremy_morley
Tel.:  +44/0 115 84 68411
Email: jeremy.morley at nottingham.ac.uk

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