stretch-live-build

Scripts supporting the build of the linuxcnc stretch live cd image

The images themselves are at http://www.linuxcnc.org/testing-stretch-rtpreempt/

Current status

When run on a Debian Stretch amd64 system, this produces an approximately 1.2GB image that can be booted via USB. It includes the 64-bit "preempt-rt" kernel, the latest linuxcnc 2.7.x "uspace" release, and uses the xfce desktop.

This is essentially untested. It will probably let your chickes out of the coop, make your goats' milk sour, etc.

Not to mention ruining machine tools galore.

The usual set of "non-free" firmware is included, but I didn't test any firmware that requires it. Because the non-free firmware is included, I expect the image to have generally the same wireless support as Debian Stretch.

Items I tested:

Boots in qemu when used as a "cdrom" installation image
installs into a 20GB virtual hard drive, using "one filesystem" partitioning. Installed system has rt kernel and linuxcnc package
Boots off a 32GB USB stick (copy with 'dd')

Important notes

The live user's name/password is user/live.
The screen locker (live-locker) is disabled by default. You can reenable it by via Session and Startup after installation.
At the live boot prompt, you can edit the kernel commandline by pressing ctrl-i (booted with bios/syslinux) or e (booted with non-secure UEFI/GRUB). This can be useful for example to enter an isolcpus= value.
After installation, root access is via "sudo" with the user's password. You can configure root access with "su" and a separate root password via "sudo passwd root".
openssh-server is installed and activated by default. This means you should only run the live image on a trusted network, and you should set a good password when installing.

Known limitations

Actual installation requires a network at install time
On most systems, the "preempt-rt" kernel is not suitable for software step generation
on a 20GB virtual hard drive, the "separate partitions" method failed, I think because the disk filled
Language packs are not included, because they caused a large increase in the download size
There's no update notifier

Hacking on it

Install the depends of live-wrapper, or just install live-wrapper. However, a local version of live-wrapper is used instead of the system one in any case.
git submodule update --init --recursive to get the live-wrapper submodule
You can select a different task by editing do.sh: Find the -t ... task-xfce-desktop line. Remove it and replace it with the task you want (e.g., task-kde-desktop).
Build the image with ./do.sh. Specify ./do.sh i386 or ./do.sh amd64 to generate just one of the two images. If there's already an image there, remove it with rm -f before invoking do.sh.
Using a caching proxy greatly speeds image generation
- I use squid-deb-proxy and set up env.sh with the line export http_proxy=http://localhost:8000/ to enable its use while lwr runs.
- squid-deb-proxy must additionally be reconfigured to allow it to access linuxcnc.org. See etc/squid-deb-proxy/mirror-dstdomain.acl.d/99-linuxcnc in the source tree for such a file (copy to /etc/squid-deb-proxy/mirror-dstdomain.acl.d/99-linuxcnc and restart squid-deb-proxy to use)
- Other proxy choices such as apt-cacher, apt-cacher-ng, and apt-proxy appear to be incompatible with live-wrapper.
Using a modified version of mksquashfs greatly speeds image generation
- An experimental patch is available at etc/mksquashfs-compression-cache.patch
- However, this will also cause a growing cache of compressed blocks in ~root/.cache which is never cleaned automatically
If you specify /dev/shm as the temporary directory in env.sh the resulting image can't install, because it looks for files like /dev/shmpool/main/….deb. (Workaround: you can use temporary directories like /tmp/shm and carefully symlink or bind-mount)

Experimental persistence

Debian Live supports keeping files you add and change on the USB drive ("persistence"). With persistence, you can keep your machine configurations and settings on the USB drive, rather than installing LinuxCNC permanently to the hard drive. Depending on the capacity of the USB drive, you can even build LinuxCNC from source.

An 8GB USB drive leaves about 6GB free for your configurations, documents, additional packages, etc. About 2/3 of this space will be used if you install LinuxCNC build-deps and source, and add a 1GB swap partition.

Perform these setup steps once as root:

use fdisk /dev/sdX to add a new partition for your root filestystem, and optionally for a swap file. (note that the first partition labeled "Empty" is actually the live image, don't modify or delete it). At this point you may need to partprobe or reboot for the new partition to be available.
mkfs.ext4 /dev/sdXY -L persistence
mount it and write to persistence.conf: / union,source=rootfs
in the unlikely event that you have a partition lableled persistence for some other purpose, you have to choose the second menu item to disable persistence.

To check that persistence worked,

Reboot
Do any operation that will change the system state (connect to a wifi network with a password, install a package, create a LinuxCNC shortcut on your desktop)
Reboot a second time. If the change you made is still there, persistence is working.

After enabling persistence you need to reenable updates, by creating the file /etc/apt/sources.list.d/updates.list as root with these contents:

deb http://ftp.debian.org/debian stretch-updates main contrib non-free
deb http://security.debian.org/debian-security stretch/updates main

Failing to do this can lead to weird problems where packages are not installable via apt due to dependency problems. (An equivalent step is automatically done by the installer when actually installing to the hard drive, but it appears to be necessary to do it manually when using persistence)

Depending on your system details, you may need to create and enable a swap file or swap partition. In order of preference, it's probably best to use a swap partition, okay to use a swap file in /lib/live/mount/persistence/sdXX, and worst to use a swap file in /.