UnicodeEncodeError when reading filenames
by mensi on Nov.02, 2010, under Python, debian
If you ever get UnicodeEncodeError exceptions when reading filenames with python, it’s probably because Apache uses the “C” locale instead of what you have configured for yourself. To fix the problem in debian, edit /etc/apache2/envvars and uncomment the line containing
. /etc/default/locale
Check that you have set the proper locale in /etc/default/locale.
Stable /dev entries with iSCSI
by mensi on Sep.04, 2010, under debian
When open-iscsi automatically logs into different targets, the resulting sdX device nodes get created depending on the order of the successful logins. Variances in network latency result in inconsistent target to device mappings. However, you can use udev do create consistent symlinks.
Create a new rules file: rules.d/55-iscsi.rules
KERNEL=="sd*", BUS=="scsi", PROGRAM="/etc/udev/scripts/iscsidev.sh %b",SYMLINK+="iscsi/%c/part%n"
And the corresponding shell script: /etc/udev/scripts/iscsidev.sh
#!/bin/sh
BUS=${1}
HOST=${BUS%%:*}
[ -e /sys/class/iscsi_host ] || exit 1
file="/sys/class/iscsi_host/host${HOST}/device/session*/iscsi_session/session*/targetname"
target_name=$(cat ${file})
# This is not an open-scsi drive
if [ -z "${target_name}" ]; then
exit 1
fi
target_name=`echo "${target_name}" | sed -r -e 's/^.*:(.*)$/\1/'`
echo "${target_name}"
If your targets are named with the scheme iqn.YYYY-MM.DOMAIN:IDENTIFIER, the rule and script will create a symlink in /dev/iscsi/IDENTIFIER/part for the corresponding /dev/sdX entry and /dev/iscsi/IDENTIFIER/partY for /dev/sdXY. This has been tested on Debian Lenny with open-iscsi.
Creating a Debian lenny XEN DomU with root on NFS
by mensi on Nov.30, 2009, under debian
An easy and simple way to manage VMs with Xen is to let linux boot off NFS, so you can serve these filesystems off a central storage machine and still have access to the complete directory hierarchy, enabling you to do fancy stuff like incremental backups. Sure, NFS is not the best way to do this, but in a low budget situation or with older hardware, this solution works quite well.
Creating a DomU for use with NFS isn’t such a hard thing, there are several possible pitfalls though. Here is a step-by-step guide:
Create empty directory on the NFS server and export it with no_root_squash for the VM itself and the xenhost or the host you want to use to bootstrap the VM
/some/dir/www.example.org www.example.org(rw,no_root_squash,no_subtree_check)
/some/dir/www.example.org xen.example.org(rw,no_root_squash,no_subtree_check)
Don’t forget to reload NFS exports
exportfs -r
Mount it on the xenhost (or the host you’re using for bootstrapping)
mkdir /tmp/www.example.org
mount -t nfs xen.example.org:/some/dir/www.example.org /tmp/www.example.org
Use debootstrap to bootstrap an initial Debian lenny install
debootstrap lenny /tmp/www.example.org/ http://mirror.switch.ch/ftp/mirror/debian
We need to do some extra things inside the VM before we can actually boot it up, so we chroot into it
chroot /tmp/www.example.org
Correctly set the hostname
echo "www" > /etc/hostname
And the hostsfile, at least localhost is required
echo "127.0.0.1 localhost" > /etc/hosts
Add and configure the loopback interface
echo "auto lo" > /etc/network/interfaces
echo "iface lo inet loopback" >> /etc/network/interfaces
Add all desired sources to /etc/apt/sources.list
nano /etc/apt/sources.list
Install the bigmem kernel for your architecture. If you do not want to do this because you already have a kernel and an initrd, at least install udev.
apt-get install linux-image-2.6-686-bigmem
Install locales to get rid of warnings regarding LC_*
apt-get install locales
dpkg-reconfigure locales
Adjust initramfs for NFS support (set BOOT=nfs instead of local)
nano /etc/initramfs-tools/initramfs.conf
Add the xen frontend drivers to the initramdisk (add xen-netfront and xen-blkfront)
nano /etc/initramfs-tools/modules
Regenerate initramdisk
update-initramfs -u all
Spawn a console on hvc0 (add the following to /etc/inittab)
0:2345:respawn:/sbin/getty 38400 hvc0
Leave chroot
[Control-D]
Copy the kernel and initramdisk to some location on the xenhost
cp /tmp/www.example.org/boot/* /vmkernel/
To be able to use NFS properly be sure to:
- DO NOT add the root to /etc/fstab as this will cause problems with the checkroot rcS script
- Add ASYNCMOUNTNFS=no to /etc/default/rcS to be able to mount additional nfs shares
Filesystem root on NFS with Debian lenny
by mensi on Sep.20, 2009, under debian
I recently updated a Debian etch machine with its root filesystem on an NFS share to lenny, which broke things a bit: During init, the filesystem somehow got remounted read-only and errors involving statd not being running occured. Additionally, other NFS mounts from /etc/fstab failed to mount at startup (but manually mounting them later worked)
I tracked down to first problem to checkroot.sh, which executes fsck if needed. Altough checkroot specifically checks for NFS being used for the root filesystem, it still tries to remount it which fails due to statd not running. This can be avoided by not adding the root filesystem to /etc/fstab so checkroot.sh will not try to do anything on it. This may be a slightly ugly workaround, but it seems to work fine.
The second problem can be worked around by setting ASYNCMOUNTNFS=no in /etc/default/rcS. I did not dive into the internals here, so I do not know the root problem causing this.
LDAP client issues in Debian lenny
by mensi on Sep.19, 2009, under debian
Apparently Debian decided to build libldap with GnuTLS instead of OpenSSL in Debian lenny, which can cause a lot of problems connecting to ldaps servers. Rebuilding the library with OpenSSL instead of GnuTLS fixed the problems for me.
Building the library by yourself is quite simple:
$ apt-get install dpkg-dev build-essential fakeroot debhelper libdb4.2-dev libgcrypt-dev unixodbc-dev libncurses5-dev libperl-dev libsasl2-dev libslp-dev libltdl3-dev libwrap0-dev debconf-utils po-debconf quilt autotools-dev libtool automake autoconf time libgnutls-dev libssl-dev
$ apt-get source libldap-2.4-2
$ cd openldap-2.4.11/
edit debian/configure-options to use OpenSSL instead of GnuTLS and then run the build. Make sure your loopback interface is configured and up and you have defined localhost in your /etc/hosts as the testsuite will fail othwerwise.
$ dpkg-buildpackage -rfakeroot -uc -us
You then should have a deb package with libldap build against OpenSSL.
If you do not want to rebuild libldap by yourself, feel free to use mine:
- debian lenny i386: libldap-2.4-2_2.4.11-1_i386.deb (md5: a5e37eb924b832192caa6312f21d7139)
- ubuntu hardy amd64: libldap-2.4-2_2.4.9-0ubuntu0.8.04.3_amd64.deb (md5: 49ccd6d71079102df6d91279b38eae1c)
Broken Downloadmanager in Firefox
by mensi on Jan.07, 2008, under Firefox
Should you ever come across a broken download manager in firefox, eg. it doesn’t pop up automatically or looks broken when opened manually, just delete the downloads.rdf in your profile folder… (which is somewhere like C:\Documents and Settings\<yourusername>\Application Data\Mozilla\Firefox\Profiles on Windows and in your home directory on UNIX based operating systems)
virtual plane-spotting
by mensi on Dec.28, 2007, under Google Maps
After virtual train-spotting, you can also do virtual plane-spotting. This Google hack was done as a diploma thesis at ZHAW. They use the transponder answers of planes near Zurich Airport to plot positions and display additional info. Imho very interesting stuff, although some may get overwhelmed by paranoia…
Homemade NAS
by mensi on Dec.28, 2007, under FreeBSD, NAS, Networking, Projects, ZFS
I finally got everything working: after some troubles with a faulty Thermaltake powersupply (It kind of died under some load; meaning one or two harddisks) and will be playing around with zfs a bit before deciding about what to use. The machine has a raw disk capacity of 2.5 TB which should be enough… at least for some weeks 
As a FreeBSD guy, I already installed 7.0-BETA4… still waiting for the RELEASE though…
Fun with Asterisk and ISDN
by mensi on Sep.08, 2007, under Asterisk, ISDN, Networking, Projects, gentoo
I recently got the idea to play around a bit with our spare ISDN line (we got ISDN back in the days when it was the only means of getting internet access and phones working simultanously) so I installed an AVM Fritz! Card PCI into “cheff” the Mini-ITX homeserver. The installation of CAPI drivers and Asterisk on gentoo is pretty straight forward, so I got a SIP phone with dialout and dialin working without problems. Now as Asterisk is quite flexible and I wanted some kind of notification of incoming calls, I built a little python script to broadcast incoming calls to the LAN. A quick and dirty C# app could then listen on a specific port and display a baloon tip whenever an incoming call occurs.
extensions.conf entry
exten => 7114988,1,System(/usr/local/bin/logcall ${CALLERIDNUM} “7114988″)
logcall
#!/bin/sh
PNUM=$1
TONUM=$2
echo “[`date`] $PNUM -> $TONUM” >> /var/log/call.log
/usr/local/bin/udp_broadcast $PNUM $TONUM
udp_broadcast
#!/usr/bin/python
from socket import *
import syss = socket(AF_INET, SOCK_DGRAM)
s.bind((”,0))s.setsockopt(SOL_SOCKET, SO_BROADCAST, 1)
s.sendto(‘call from: ‘+sys.argv[1]+”\nto: “+sys.argv[2], (‘<broadcast>’, 50000))
outdoor networking
by mensi on Aug.07, 2007, under Networking, Projects, WiFi
I recently had the chance to play around with a LaserBit Wireless Cable. It is very easy to use: I just acts like a straight LAN cable and comes with RJ45 connectors. Setting it up is pretty simple in theory: fix each transceiver on something and point them at each other; alignment however is quite tricky over large distances because you can’t actually see the laser; it’s IR. We had quite some trouble with our ~600m setup but finally managed to establish a stable link. It only held for one day though as one end was attached to a large tent; obviously not the best thing but our only option. We previously tried to use 2.4Ghz helix antennas (~14db gain) and standard WLAN, but it failed miserably at about 200m due to several obstacles and a little hill.
The whole setup: (internet access for a camp)
We got ADSL from a nearby farm, attached an ADSL modem and a WRT54GL accesspoint which provided coverage for an AP in client mode attached to one end of the Wireless Cable. The other end was at the top of a tent, attached to another WRT54GL, which provided covergage for the camp. Another WRT widened the range (per WDS) and had a printer attached.
It was an interesting project, however it was never used at its intended purpose; sometimes the laser had to be realigned, sometimes the ADSL connection dropped (the farm itself was quite abroad, so the line quality wasn’t that great…)
