Category: Raspbian

raspberry pi 4 status report for 10 april 2020 – running pretty good these days

whbeebe

If there’s one thing I’ve been critical of with regards to the Raspberry Pi 4, it’s been the fact it runs hotter than any prior Raspberry Pi. I run my Pi 4s in a Flirc case (https://flirc.tv/more/raspberry-pi-4-case) in order to keep them as cool as possible during operation. Yet as good as the Flirc case is, the Pi 4 with the Raspbian initial release still easily hit the mid-50°Cs (or hotter) with just regular usage. Recently I’ve noticed that the Pi 4, with the latest version of Buster (including all patches) and the firmware, is running a good 10°C cooler, around the mid-40°C or cooler. When I now put my hand on the case it’s barely warm, not the hot little brick when I first put the Raspberry Pi 4 in the case.

In addition to running cooler, Raspbian Buster appears to be using a lot less memory resources than before, such as when having many open tabs in Chromium. More often than not I could see on htop where swap was being hit with a regular load of Chromium, multiple open tabs on the Terminal with multiple editing sessions, and regular builds with any of Go, C++, Rust, Python 3 or Julia running. I’ve now had the Pi 4 up for five days with continuous use and I haven’t hit swap yet.

And speaking of Julia, I installed version 1.4.0 and then installed all the supporting packages I normally need. One of those packages is Winston, and it has problems. Winston under Julia 1.4.0 is dependent on more packages than ever these days, so much so that any Julia script I’ve written won’t run because not all the current Winston dependencies are met. As a consequence I’ve dropped back to running the prior release, Julia 1.3.1. My scripts still run, and for the time being I’m not updating any of its packages.

ugly surprises with raspbian buster and external file systems

whbeebe


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/swapCONF_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.