Linux Embedded devices with PicoDebian Martin Noha

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Embedded systems

Linux Embedded devices

with PicoDebian

Martin Noha 28.9.2006

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Agenda

 Why did I look in this stuff ?  What is an embedded device?  Characteristic hardware  global requirements for software  some small distributions  Pico Debian out of the box  Customizing

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Why did I look in this stuff ?

• Security

• costs

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Why did I look in this stuff (2) ?



DSL termination

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AP



basic services

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firewalling

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reporting

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compliant with dummies (girl friend)

Conclusion: I want an embedded device

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What is an embedded device?



no noise

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no hard disk, no fan > no moving parts

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may need keyboard and monitor

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Not very powerful processor

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Limited memory (64 – 128 MB)

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Compact flash instead of hard disk

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Limited capability for extensions

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Characteristic hardware

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Characteristic hardware (2)

http://www.soekris.com

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Characteristic hardware (3)

http://www.lex.com.tw

Keyboard and

Monitor connector

Supports harddisk

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global requirements for software

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ability to boot from flash

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no write access to flash

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read only file system

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Capability to run within limited resources

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flexible configuration

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some small distributions

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Embedded Debian

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Monowall

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DSL (Dammed Small Linux)

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Trinux

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Linux Router Project



Pebble > pyramid Linux

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PicoDebian

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PicoDebian out of the box

 thinneddown version of the Debian Sarge  hardware support depends on kernel  uses Squashfs  has two partitions (root and boot)  generates RAM disk at boot  image generation on development server  configuration in chroot env. on dev. server  Runs with 32MB CompactFlash  Consists of two parts

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PicoDebian out of the box (2)

Advantages

 flexible – with all Debian packets in the background  Same administration like a standard Debian system

Disadvantages

 Squashfs requires new image and reboot for each config change  chroot env has problems with module installation  devices may miss in /dev  all logs are deleted at power down

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PicoDebian out of the box (3)

Scripts are used for Image generation  setting up the chroot environment Installation process  Partitioning of flash in dev server  install boot loader (grub) in MBR  Adopt boot image to size of boot partition  adopt system specific parameter e.g. fd device, boot parameter, mount table, root password, etc.

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PicoDebian out of the box (4)

what can go wrong – what went wrong   no monitor – no info about boot process > serial connection needed  kernel not found > reconfigure grub Panic because of wrong root device > reconfigure grub  network device not supported > new kernel needed  no access because of missing passwords > …

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PicoDebian customizing PicoDebian customizing tecnical track tecnical track

Customizing step 1

 own kernel without modules  kernel update impacts only /boot  change of partitions – adding a seconded system  extending the scripts Mainly adding a copy function and parameter  adding a RW section in the boot partition that is copied to the RAM disk at boot

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PicoDebian customizing (2) PicoDebian customizing (2) tecnical track tecnical track

Customizing step 2

 integrating unionfs  change of partitions – adding a 5 MB system  HW adding an Atheros based WLAN mini PCICard  adding madwifi driver to kernel – building AP  kernel must support modules again Kernel installation is more complex E.g depmod –a does not work in chroot

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Customizing Kernel

 download from www.kernel.org and unpack …  patch with squashfs  patch with unionfs  patch with …  configure new options  Make debian kernel package, unionfstools, madwifimodules  Install kernel, and unionfstools and

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PicoDebian customizing (2) PicoDebian customizing (2) tecnical track tecnical track  selection at boot – via grub or predefined 10MB /boot Hda1 ext2 25 MB / update system Hda2 Squashfs 50 MB / (normal) root Hda3 Squashfs 5 MB for union FS ext2 / /boot /etc /root /…. / /boot /etc /root /…. Normal operating Update mode

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Update method

 enter chroot env on devserver  modify elements (aptget update, upgrade …)  generate image  boot into update mode  transfer image for hda1 and hda 3 (dd via ssh)  and reboot  „copy“ main env to update env  Generate update image and transfer to hda2

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Services running

 DSL termination  Default system applications (syslog etc)  iptables “firewall” with wondershaper  basic services ntp, dns, dhcp, ssh, snmpd  squid  some ipv6 stuff (not relevant)  Dyndns client  Hostapd and radius  bridge

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Versions

 based on debian sarge (tried ubuntu too)  Kernel 2.6.17.11  Squashfs 3.0 (supports up to 2.6.15 officially)  snapshot of unionfs (2006/06/20) official release supports only 2.6.15.x  Madwifi 0.91  hostapd with 801.x authentication (TLS)  Radius server

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PicoDebian rescue system for PicoDebian rescue system for mailserver mailserver

Different use case

 rescue system for a company mail server  boots by default into a PicoDebian installation  offers maintenance without mounted filesystem  needes one partition and 50 MB  remote hands needs to press reset only  all filemgt toos are includes in the image  kernel has to be patched with squashfs  uses same kernel as productive system

Linux Embedded devices with PicoDebian Martin Noha

Embedded systems

Embedded systems