X-Git-Url: https://pere.pagekite.me/gitweb/homepage.git/blobdiff_plain/43afa7e32e2d9f7be65988f2d98a5d95db5e7f5a..9874ebb15b7a85d0d6e59d17eb4a66c9cb704948:/blog/index.html diff --git a/blog/index.html b/blog/index.html index 24d4f2adef..91f4f77ab1 100644 --- a/blog/index.html +++ b/blog/index.html @@ -19,6 +19,90 @@ +
+
Automatic proxy configuration with Debian Edu / Skolelinux
+
13th February 2012
+

New in the Squeeze version of +Debian Edu / Skolelinux is the +ability for clients to automatically configure their proxy settings +based on their environment. We want all systems on the client to use +the WPAD based proxy definition fetched from http://wpad/wpad.dat, to +allow sites to control the proxy setting from a central place and make +sure clients do not have hard coded proxy settings. The schools can +change the global proxy setting by editing +tjener:/etc/debian-edu/www/wpad.dat and the change propagate +to all Debian Edu clients in the network.

+ +

The problem is that some systems do not understand the WPAD system. +In other words, how do one get from a WPAD file like this (this is a +simple one, they can run arbitrary code):

+ +
+function FindProxyForURL(url, host)
+{
+   if (!isResolvable(host) ||
+       isPlainHostName(host) ||
+       dnsDomainIs(host, ".intern"))
+      return "DIRECT";
+   else
+      return "PROXY webcache:3128; DIRECT";
+}
+
+ +

to a proxy setting in the process environment looking like this:

+ +
+http_proxy=http://webcache:3128/
+ftp_proxy=http://webcache:3128/
+
+ +

To do this conversion I developed a perl script that will execute +the javascript fragment in the WPAD file and return the proxy that +would be used for +http://www.debian.org/, +and insert this extracted proxy URL in /etc/environment and +/etc/apt/apt.conf. The perl script wpad-extract work just +fine in Squeeze, but in Wheezy the library it need to run the +javascript code is no longer +able to build because the C library it depended on is now a C++ +library. I hope someone find a solution to that problem before Wheezy +is frozen. An alternative would be for us to rewrite wpad-extract to +use some other javascript library currently working in Wheezy, but no +known alternative is known at the moment.

+ +

This automatic proxy system allow the roaming workstation (aka +laptop) setup in Debian Edu/Squeeze to use the proxy when the laptop +is connected to the backbone network in a Debian Edu setup, and to +automatically use any proxy present and announced using the WPAD +feature when it is connected to other networks. And if no proxy is +announced, direct connections will be used instead.

+ +

Silently using a proxy announced on the network might be a privacy +or security problem. But those controlling DHCP and DNS on a network +could just as easily set up a transparent proxy, and force all HTTP +and FTP connections to use a proxy anyway, so I consider that +distinction to be academic. If you are afraid of using the wrong +proxy, you should avoid connecting to the network in question in the +first place. In Debian Edu, the proxy setup is updated using dhcp and +ifupdown hooks, to make sure the configuration is updated every time +the network setup changes.

+ +The WPAD system is documented in a +IETF +draft and a +Wikipedia +page for those that want to learn more. +
+
+ + + Tags: debian edu, english. + + +
+
+
+
Skolelinux-intervju: Axel Bojer
7th February 2012
@@ -570,52 +654,6 @@ on the project announcement list.

-
-
Fixing an hanging debian installer for Debian Edu
-
3rd January 2012
-

During christmas, I have been working getting the next version of -Debian Edu / Skolelinux ready -for release. The initial problem I looked at was particularly -interesting.

- -

The installer would hang at the end when it was doing it -post-installation configuration, and whatevery I did to try to find -the cause and fix it always worked while I tested it, but never when I -integrated it into the installer and ran the installation from -scratch. I would try to restart processes, close file descriptors, -remove or create files, and the installer would always unblock and -wrap up its tasks.

- -

Eventually the cause was found. The kernel was simply running out -of entropy, causing the Kerberos setup to hang waiting for more. -Pressing keys was adding entropy to the kernel, and thus all my tries -to fix the problem worked not because what I was typing to fix it, but -because I was typing.

- -

The fix I implemented was to add a background process looking at -the level of entropy in the kernel (by checking -/proc/sys/kernel/random/entropy_avail), and if it was too small, the -installer will flush the kernel file buffers and do 'find /' to -generate some disk IO. Disk IO generate entropy in the kernel, and is -one of the few things that can be initated from within the system to -generate entropy.

- -

The fix is in -beta1 -of the Debian Edu/Squeeze version, and we -welcome more testers and -developers. We plan to release beta2 this weekend.

-
-
- - - Tags: debian edu, english. - - -
-
-
-

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