pi-gen: Choosing the package to install or to skip

Pi-gen has nicely divided the build process into stages so that we can choose which stages to build and which stages to skip. However, within a stage, sometimes there are still packages that we want to include or exclude. For example, I like to use the vim text editor which is not included anywhere. I see that stage2 is where system packages are installed, so I added vim at the end of stage02/01-sys-tweaks/00-packages.

I haven’t used Epiphany browser before, and I think I only need Chromium for my project. So I can save some build time and some disk space by excluding it from my packages. Basically I removed the line with ephibany-browser from stage3/00-install-packages/00-packages-nr.

One thing that intrigued me was the difference between the file names for 00-packages and 00-packages-nr, and in some folders both files are present. So what determines which package should be in which file? I took a look at build.sh and the answer is there:

  • For packages defined in 00-packages, the command to install the packages is apt-get install -y $PACKAGES
  • For packages defined in 00-packages-nr, the command to install the packages is apt-get install --no-install-recommends -y $PACKAGES
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pi-gen: Stage Specification

In the GitHub page for pi-gen, there is a section on Stage Specification. However the example there is a little misleading. I wanted to run until stage3 and export an image from that stage, but because the example showed only touching the SKIP files, I did not realised that the EXPORT_IMAGE file is what the export script was looking for (until I read the export script….).

So basically in a nutshell:

  • SKIP files will only instruct pi-gen which stages to skip, nothing to do with any image export
  • EXPORT_IMAGE is required in the folder for which the stage you want an image to be exported.

The image suffix can be configured, just put a one-line IMG_SUFFIX="-my-own-image" in the EXPORT_IMAGE file at the appropriate stage folder.

pi-gen: Starting chromium into kiosk mode upon start-up

In my use-case, I want the GUI to start Chromium into kiosk mode. This is done by putting settings into the autostart file.  Stage3 in pi-gen is where the GUI is first installed, so I used the 01-tweaks sub-stage to specify this.

I added the folder files under stage3/01-tweaks and created a file autostart with the following contents:

@lxpanel --profile LXDE-pi
@pcmanfm --desktop --profile LXDE-pi
@xset s off
@xset -dpms
@xset s noblank
@sed -i 's/"exited_cleanly": false/"exited_cleanly": true/' ~/.config/chromium-browser Default/Preferences
@chromium-browser --noerrdialogs --kiosk http://apple.com --incognito --disable-translate

Note that I used apple.com in this example. You can use whatever URL you like.

To copy the above file into the correct place in the image, we need to add the following lines at the end of stage3/01-tweaks/00-run.sh:

install -v -d                         ${ROOTFS_DIR}/etc/xdg/lxsession/LXDE/
install -v -m 644 files/autostart     ${ROOTFS_DIR}/etc/xdg/lxsession/LXDE/

The first line creates the LXDE folder in the image and the second line copies the autostart file above to the /etc/xdg/lxsession/LXDE/ folder in the image.

pi-gen: Enabling ssh by default

There are some system services that you can enable or disable by default. ssh is disabled by default, which I presume is due to security reasons, but for my purpose it is easier to manage the RPi’s if I have ssh access. For a start, I want my RPi’s to listen to ssh, will be putting in the security measures gradually.

To enable ssh by default, change stage2/01-sys-tweaks/01-run.sh:

-systemctl disable ssh
+systemctl enable ssh

There are other services in this page that you can choose to enable or disable

pi-gen: Timezone and Locales

The tweaks here are minor, Just documenting so that I will not forget. The changes relevant to me are:

In stage0/01-locale/00-debconf

-tzdata	tzdata/Areas	select	Etc
+tzdata	tzdata/Areas	select	Asia

and

-tzdata	tzdata/Zones/Etc	select	UTC
+tzdata	tzdata/Zones/Etc	select	GMT+8

In stage2/01-sys-tweaks/00-debconf

-keyboard-configuration	keyboard-configuration/xkb-keymap	select	gb
+keyboard-configuration	keyboard-configuration/xkb-keymap	select	us

One thing to note that it is through this that I know that the “|” character is not on the default GB keyboard layout, have to change it to the US Keyboard.

pi-gen: Setting default WiFi settings

In Raspbian, the WiFi settings are found in /etc/wpa_supplicant/wpa_supplicant.conf. In my use case, all my RPis are in the same WiFi network, and it is easier for me to write that setting in the image.

Before writing the settings, we also need to get the pre-shared-key (psk) in hashed mode instead of storing it in the clear in the .conf file. To get the hashed psk, do the following at the command line:

wpa_passphrase [SSID] [wifi password]

for example:

wpa_passphrase MarvelWorld SpideyIsHome2017

which will return

network={
  ssid="MarvelWorld"
  #psk="SpideyIsHome2017"
  psk=8b2972afc8724ff207bac00980457759e49eb089223a151db142503994e72b9d
}

put this into stage2/02-net-tweaks/files/wpa_supplicant.conf:

country=SG
ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
update_config=1

network={
  ssid="MarvelWorld"
  #psk="SpideyIsHome2017"
  psk=8b2972afc8724ff207bac00980457759e49eb089223a151db142503994e72b9d
}

Note that I changed the country to SG. You should change it to where you are using the RPi.

pi-gen: Changing the Mirror Site URL

There are two ways to run pi-gen, one is to run it within a host that calls the build.sh script to build the image, and the other is to run it within a docker image which in turns calls the same build.sh script. Both works and both take an awful amount of time.

Sometimes this is made worse by the mirror site not responding in time, or somehow serving the wrong headers or the files with the wrong Hash number.

[To do, add the actual error messages]

One way to work around this is to manually put in a different mirror site URL. I got the idea from https://www.reddit.com/r/raspberry_pi/comments/4bl4ia/mirrordirectorraspbianorg_not_working/ which suggested using http://mirror.leaseweb.com, which will automatically give you a site that is geographically close to your site. However, this is what the original mirrordirector.raspbian.org would already have done, and it sometimes still fails.

What I have done was to refer to https://www.raspbian.org/RaspbianMirrors, and choose the site that I feel is closest to me or fastest to load. This might not be very scientific, but it is good enough. If you want to get one more step more scientific, you can install the Page load time Chrome extension from https://github.com/alex-vv/chrome-load-timer which will tell you the time a page is loaded. Click on the http links in the RaspbianMirrors page and determine a site that is fast enough for yourself. I found a few with load time of 0.33 seconds or there about.

Once I find a mirror site I want to use (in my case http://mirror.premi.st, I don’t know why but for some reason a South Korea site is fast for me in Singapore), I can change the following files in pi-gen:

stage0/prerun.sh


#!/bin/bash -e
if [ ! -d ${ROOTFS_DIR} ]; then
bootstrap jessie ${ROOTFS_DIR} http://mirror.premi.st/raspbian/raspbian
fi

stage0/00-configure-apt/files/sources.list


#deb http://mirrordirector.raspbian.org/raspbian/ jessie main contrib non-free rpi
deb http://mirror.premi.st/raspbian/raspbian/ jessie main contrib non-free rpi