Debian and Ubuntu changed the default shell /bin/sh from bash (Bourne Again Shell) to dash (Debian Almquist Shell).

The advantage of dash is its size, speed and POSIX compliance. The disadvantage is that many scripts written for bash won't work anymore because bash has specific features - so called "bashisms".

 

One of this bashisms, I used frequently in the xxsvideo build system is the " indirect variable expansion". Which makes it possible to execute the following script:

#!/bin/bash                                                                                                                                        
                                                                                                                                                   
CONFIG_BUSYBOX=y

PACKAGENAME="BUSYBOX"
PACKAGECONFIG=CONFIG\_$PACKAGENAME

if [ "${!PACKAGECONFIG}" = "y" ]; then
        echo $PACKAGENAME "is selected"
else
        echo $PACKAGENAME "is NOT selected"
fi

If you call this script with bash you receive as expected "BUSYBOX is selected".

With dash you see:

./test.sh: 13: Bad substitution

I was looking a long time for the right way to replace this {!VAR} statement. But it's quite simple and suddenly I found a thread describing it:

#!/bin/dash

CONFIG_BUSYBOX=y

PACKAGENAME="BUSYBOX"

PACKAGECONFIG=CONFIG\_$PACKAGENAME

if [ "$(eval echo '$'$PACKAGECONFIG)" = "y" ]; then

    echo $PACKAGENAME "is selected"

else

    echo $PACKAGENAME "is NOT selected"

fi

 

In short: With dash you write:

eval echo '$'$VARIABLE

which is equivalent to bash

echo ${!VARIABLE}

 

... I think ;-)

 

I'm using a Fritz!Box Fon WLAN 7170 as Hotspot in my caf'e. The DSL speed is 6000kBit/s and I only want people use 1MBit/s maximum. The Fritz!Box offers traffic shaping only to prioritize VOIP over common traffic.

 

If you have linux box, you may use the tc command to do the following traffic shaping using class based queues (cbq):

 

 

#!/bin/sh

DEV=eth0

DEV=tiwlan0

TC=tc

RATE=768kbit

# erase all old

$TC qdisc del dev $DEV root

# set new

modprobe cls_u32

$TC qdisc add dev $DEV root handle 1: cbq avpkt 1000 bandwidth 10mbit

$TC class add dev $DEV parent 1: classid 1:1 cbq rate $RATE \

             allot 1500 prio 5 bounded isolated

$TC filter add dev $DEV parent 1: protocol ip prio 16 u32 \

         match ip dst 0.0.0.0/0 flowid 1:1

Ok, this is a very hard limit of 768kBits/s for the whole WLAN-interface of the Fritz!Box. Of course you may add lter rules for specific hosts, ports, netmasks or whatever. See the lartc-guide for details.

 

So far theory. But how to get this stuff working on the Fritz!Box? I found the Freetz-project which modifies the original firmware. You may add kernel modules, some applications and a new webinterface.

1. checkout freetz-stable-1.0 from SVN (freetz-stable-1.1 didn't work with my box - it rebootet every 10 seconds)
2. do a config and build (make menuconfig; make) and install the image in images/
3. add the modules sch_cbq,ko and cli_u32.ko to kernel/Config.in
4. apply my patch add-iproute2-freetz-1.0.patch
5. make menuconfig; make and install the new image

This is a very rough howto. Don't hesitate to ask you questions as comment.

For half a year, I have a Jetway Nano-ITX Board (J8F9) running with Xubuntu 8.04 on a CF-card. This Board is very slow with an AMD Geode but 100% silent and consumes only about 3 Watt. It's the perfect internet client for my cafe.

 

One problem was the right setting for the display (quite cheap monitor with 1440x900 pixels). Before updating to 8.10 I had to edit the /etc/X11/xorg.conf manually and set:

 

Section "Device"
        Identifier    "Configured Video Device"
      #Option  "UseFBDev"  "true"
        Driver    "fbdev"
EndSection

Section "Screen"          
       Identifier   "Default Screen"          
       Monitor   "Configured Monitor"          
       Device  "Configured Video Device"          
       DefaultDepth  24          
       SubSection "Display"         
    # Virtual 1440 900          
       Modes  "1440x900" "1280x1024" "1024x768"          
      EndSubSection 
EndSection 

 

The Xorg-Version is:

 

X.Org X Server 1.4.0.90

Release Date: 5 September 2007

X Protocol Version 11, Revision 0

Build Operating System: Linux Ubuntu (xorg-server 2:1.4.1~git20080131-1ubuntu9.

Current Operating System: Linux cafepc 2.6.24-19-generic #1 SMP Wed Aug 20 22:5

Build Date: 13 June 2008  01:08:21AM

 

 

After 5 minutes download and about 6 hours (!) packages replacements, the system was ready to reboot. But... it ends up in a kernel panic! And before booting, the install-tool deinstalled the old kernel. Very stupid.

 

So I removed the CF-card and modified the boot/grub/menu.lst. Xubunto forgot to add the initrd-line below the kernel:

 

initrd  /boot/initrd.img-2.6.27-14-generic