building emacs 28 on jetpack 4.4 developer preview

By now all of this blog’s readers should realize that when I write about Nvidia’s Jetpack 4.4 Developer Preview (here-after called JP44), I mean the version of Ubuntu 18.04.4 with Nvidia’s software extensions and packages installed.

Earlier I installed all the bits and bobs necessary to build Visual Studio Code on JP44, and managed to get it up and running, mostly. That is, it would open and edit files, it handled syntax highlighting for the sources I cared about, and at least it allowed me to install two extensions. The big problem is that after that first extension installation, the extension list is now empty, meaning I can’t install any others. And I wrote I’d probably stick with it regardless.

Then I remembered I’d extended and configured both Vim and Emacs into very useful tools on my RPi4. I powered up the RPi4 and copied my Vim and Emacs configuration files over to the Jetson Nano and JP44. Easy, right?

For Vim there wasn’t an issue. Everything ran just fine. Emacs installed from the repo was different. I knew I had a problem when the following line in my .emacs file failed on startup with the local emacs:

(global-display-line-numbers-mode)

I checked the version of emacs installed on JP44, and sure enough, it was version 25, one major release back from the version installed on my RPi4 and Raspbian. No, I wasn’t going to change that line (and a few others) back to the older way of doing things. Instead I went over to the Project Emacs page on Savannah ( http://savannah.gnu.org/projects/emacs/ ), followed the directions there to clone from their GitHub repo hosted on Savanah, and went about the business of building an up-to-date emacs.

First time through I was missing a few needed development libraries. I got those installed, got a proper configuration, and then built it. When I fired it up I was horrified to see it was using old school X fonts on everything. Not an anti-aliased font in sight. That just sucked, so I starting looking at the configure output and installing all the necessary libraries emacs needed to support anti aliased fonts. The full list of necessary installs are:

  • texinfo
  • libxaw7-dev
  • libjpeg-dev
  • libpng-dev
  • libgif-dev
  • libtiff-dev
  • gnutls-dev
  • libncurses-dev
  • libfreetype6-dev
  • libcairo-dev

Some of those libraries are needed just to get configure to finish at all. They are listed in the order they were installed. After installing the freetype developer library I got the following interesting warning from configure:

configure: WARNING: This configuration uses libXft, which has a number of
    font rendering issues, and is being considered for removal in the
    next release of Emacs.  Please consider using Cairo graphics +
    HarfBuzz text shaping instead (they are auto-detected if the
    relevant development headers are installed).

Ok. That’s when I installed libcairo-dev. After that it configured and then built. ‘make install’ puts the binary in /usr/local/bin. When I opened up emacs the second time, it was lovely to behold.

Fonts everywhere are nicely rendered and anti-aliased. You’ll note also that this is emacs version 28, which is fine by me. It works with Go, C/C++, Python, and bash, which is all I really need. I also noticed that emac’s memory footprint is tiny compared to VSCode. Which is ironic considering that in the days when men used Vaxen and 1MiB of memory was considered a luxury, emacs was frowned upon by sysadmins who didn’t like how too many emacs sessions could tax those mighty Vaxen. Now I run it on a $100 quad-core 64-bit computer with 4GiB of memory because it’s lean and mean compared to other equivalent tools. My how the times have changed.

ugly surprises with raspbian buster and external file systems


A while back I wrote about adding an SSD to a Raspberry Pi 4 and modifying /etc/fstab so that it would automatically mount when it booted. This is different than having it automount through /media/pi, since that type of automount only occurs after the OS is fully up and then scans for attached devices, such as those on USB. For nearly all use cases you can’t tell one from the other. But for those very few use cases where you need the kernel to mount the attached storage device before the rest of the system comes up, you need to define it in /etc/fstab.

That wasn’t a problem with Raspbian Buster up until just recently. Before that time, I had an entry for my SSD in fstab that started out like this:

/dev/sda1 ...

It worked just fine, until one day after a recent update that included the kernel, it didn’t. No warning that this was going to happen, none at all. After the update and subsequent reboot, the Raspberry Pi refused to boot, and instead dropped me into a prompt waiting for me to log in as root to fix the problem. Oh, wait, root is disabled by default in Raspian, so that just put me in an endless boot loop.

It took two attempts rebuilding a minimal boot micro SDXC before I finally figured out what was happening. Fortunately, that second micro SDXC card was a new one with a minimal Raspbian system, so it didn’t take too much effort to see that adding the entry to /dev/sda1 was causing it to fail to boot. Fortunately for me I have other Linux systems (my ten-year-old Samsung R580 running Ubuntu 18.04.04 came to the rescue) that allowed me to mount both micro SDXC cards, edit fstab and remove the entries. Once removed, both micro SDXC cards booted just fine in the Raspberry Pi 4.

Once I got back in I enabled root with ‘sudo passwd root’ and gave it a password. Now, if I have a problem where a Raspbian boot failure wants to dump me into the root account in single user mode, I can actually log in at that point.

The other problem was getting the USB SSD to mount. Here’s what I did to fix that. But first, a tiny bit of background.

The kernel in Raspbian buster uses what’s now known as a PARTUUID to identify a storage device instead of the old school device name in /dev. To find out what that PARTUUID is, you have to run this command at the command line in a terminal window:

pi@rpi4-4-01:~ $ sudo blkid
/dev/mmcblk0p1: LABEL_FATBOOT="boot" LABEL="boot" UUID="69D5-9B27" TYPE="vfat" PARTUUID="d9b3f436-01"
/dev/mmcblk0p2: LABEL="rootfs" UUID="24eaa08b-10f2-49e0-8283-359f7eb1a0b6" TYPE="ext4" PARTUUID="d9b3f436-02"
/dev/sda1: LABEL="SSD" UUID="ad89d540-a007-4d0a-887b-0b0dbefe3e8e" TYPE="ext4" PARTUUID="937a0120-01"
/dev/mmcblk0: PTUUID="d9b3f436" PTTYPE="dos"

Since I already know the label on my SSD is “SSD” it’s quickly identifiable in blkid’s output. Copy the PARTUUID at the end of the entry, and use that in the fstab entry for the drive, like so:

PARTUUID=937a0120-01 /ssd ext4 defaults,auto,users,rw,nofail,x-systemd.device-timeout=30 0 0

Note that the quotes are not added to the entry. Also note all the flags I use, especially the shortened timeout (systemd.device-timeout=30) to shorten the wait during boot in case the SSD isn’t plugged in. The default is 90 seconds.

The primary reason I want the SSD mounted is because that’s where I put swap. In /etc/dphys-swapfile I add the following line:

# where we want the swapfile to be, this is the default
#CONF_SWAPFILE=/var/swap
CONF_SWAPFILE=/ssd/swap

I want my swap on the SSD because testing has shown the SSD is an order of magnitude faster than the boot micro SDXC. I use the Raspberry Pi 4’s as development and native build machines, rather than set up an emulation and cross-compile tool chain on my Mac. Believe it or not, it’s a lot simpler the way I have it set up. This is a decent compromise that doesn’t require me to put the entire OS on the SSD and then configure the Raspberry Pi to boot off the SSD. There are some significant problems with that, such as the Rasberry Pi 4 wasn’t set up to do that for quite some time after its release, and the fact that once configured that way, you can’t go back. So I put swap on the SSD, then cd onto a work area on the SSD and develop and build away.

This all gets back to the bigger question: why did this change, and when did it change? I use the same type of setup, and the same SSD, on the Jetson Nano, and it’s running a tweaked version of Ubuntu 18.04.04, complete with the Ubuntu graphical desktop. The fstab entry for that is the regular device entry, /dev/sda1.

Oh well. I just keep reminding myself that this is just a hobby, and I’m retired.