Netlive is a slightly unusual distribution developed in Italy: a live version of Linux that makes available on demand any other live version of Linux chosen by its administrators to all the computers of its local network. Its developers, Ezio Da Rin and Marco Clocchiatti, call Netlive “a very efficient way to build portable ICT labs for schools, alternative to the Linux Terminal Server Project (LTSP)“. The practical advantages of Netlive for end users, that is schools and students, have been already explained elsewhere. This page, instead, explains Netlive’s internal architecture and what makes it different from LTSP.
What’s inside Netlive?
Technically speaking, Netlive is a text-only Debian-Live distribution, modified in order to export via NFS a special folder. This folder contains a Squashfs file system, that each client mounts as aufs. That file system can be any Linux distribution you want. The Netlive website currently hosts the ISOs for serving ITIS Linux, SoDiLinux, or an italian version of Linux Mint. The basic method and the building scripts, however, can be easily modified to include any other version of Linux, in whatever language you prefer. You take the ISO image of whatever distro you want to serve via Netlive, mount it, chroot into it and modify the distro, using its native package manager or messing with the configuration files in /etc/, in whatever way you want.
The next step is to generate an initramfs to boot that system in the clients. Netlive applies a Gentoo technique to the Debian-Live tool live-initramfs, in the same way you’d work to customize Ubuntu from scratch (even if Ubuntu uses casper).
Netlive performances
According to Ezio, the Netlive Server can even run on a P3, 866 MHz computer. The clients must be more powerful instead (see next paragraph). When you boot them, the clients do not need to download the complete Squashfs file system, in order to start working, so a whole lab can be up and running in very little time. You may experience latencies in some circumstances, for example if 20 clients tried to open OpenOffice in the very same moment over a very slow LAN, because even the server on the live DVD doesn’t load the whole Squashfs. Otherwise, the first user may notice a slow loading of OpenOffice, but all the others wouldn’t, because it would be already present in the server RAM.
Accessing files from a CD-ROM or USB key can be slower than from normal hard disks. However, Marco and Ezio told me that using compressed images in Squashfs format makes up for the slower speed of optical disks and, when using USB keys, can even be faster than accessing files from a non compressed file system on a hard disk. Besides, the network load is minimized, because every client requests from the server only the (compressed!) image of the application they want to run, not the whole operating system.
Netlive or LTSP? It depends on the hardware
Netlive offers to its end users almost the same service as LTSP, but turning some features and requirements of the latter upside down. Due to its way of working, Netlive can perform better in all the cases where the clients are powerful enough that LTSP would under-utilize them. With Netlive, all the applications run in the clients, not in the server. Therefore, Netlive needs relatively modern clients, even if very cheap ones are enough (1), but has no need for a powerful server, LTSP is just the opposite. Besides, Netlive gives the students a fully autonomous, complete system, that they can modify in every possible way because any change is both local and limited to the current session. You can’t offer that kind of freedom with LTSP.
For this reason, Ezio and Marco think (as they also explained in another interview) that Netlive may become more popular than LTSP among teachers who must work in computer labs where they can’t install Free Software but can’t afford to waste time manually booting 20⁄30 PCs from live distros at every lesson. Ezio also points out that not only new, low-end desktop computers become cheaper and cheaper every year, they also are much more reliable, energy-efficient and easier to maintain up and running than refurbished machines. Therefore, many schools may decide that accepting old, donated computers costs more, in the long run, than buying cheap, new ones. In all those cases, Netlive may use their hardware resources more efficiently than LTSP.
What do you think? Please let us know, either adding a comment or directly writing to ezio, at linuxnetlive.org (webmaster note: I will addd antispam filters to allow comments from anonymous users as soon as possible. In the meantime, please be patient and register, if you want to comment, thanks!)
(1) Ezio recently explained on the italian Debian list that you could build a great Netlive client with new components spending less than 200 Euro.