Update on earlyoom

Back in Linux Behavior Without Swap, I noted that the modern Linux kernel will still let the system thrash.  The OOM killer does not come out until it is extremely desperate, long after responsiveness is near zero.

It has been long enough since installing earlyoom on our clouds that I did another stupid thing.  earlyoom was able to terminate the script, and the instance stayed responsive.

I also mentioned “swap on zram” in that post.  It turns out, the ideal use case for zram is when there is no other swap device. When there’s a disk-based swap area (file or partition), one should activate zswap instead.  zswap acts as a front-end buffer to swap, storing the compressible pages, or letting others go to the swap device.

One other note, zswap is compiled into the default Ubuntu kernels, but zram is part of the rather large linux-modules-extra package set.  If there’s no other need for the extra modules, uninstalling them saves a good amount of disk space.

Upgrading a debootstrap'ped Debian Installation

For context, last year, I created a Debian 11 recovery partition using debootstrap for recovering from issues with the 88x2bu driver I was using.

This year, I realized while reading that I have never used anything but Ubuntu’s do-release-upgrade tool to upgrade a non-rolling-release system.  My Debian 12 desktop felt far less polished than Ubuntu Studio, so I reinstalled the latter, and that means I once again don’t need the 88x2bu driver.

Therefore, if I trashed the Debian partition, it wouldn’t be a major loss.  It was time to experiment!

Doing the upgrade

The update process was straightforward, if more low-level than do-release-upgrade.  There are a couple of different procedures online that vary in their details, so I ended up winging it combining them:

1. apt update
2. apt upgrade
3. apt full-upgrade
4. apt autoremove --purge
5. [edit my sources from bullseye to bookworm]
6. apt clean
7. apt update
8. apt upgrade --without-new-pkgs
9. apt full-upgrade
10. reboot
11. apt autoremove

DKMS built the 88x2bu driver for the new kernel, and userspace appeared to be fine.

Fixing the Network

The link came up with an IP, but the internet didn’t work: there was no DNS.  I didn’t have systemd-resolved, named, dnsmasq, nor nscd.  Now, to rescue the rescue partition, I rebooted into Ubuntu, chroot’ed to Debian, and installed systemd-resolved.

Fixing Half of the Races

One of the Debian boots left me confused.  Output to the console appeared to have stopped after some USB devices were initialized.  I thought it had crashed.  I unplugged a keyboard and plugged it in, generating more USB messages on screen, so I experimentally pressed Enter.  What I got was an (initramfs) prompt!  The previous one had been lost in the USB messages printed after it had appeared.

It seems that the kernel had done something different in probing the SATA bus vs. USB this time, and /dev/sdb3 didn’t have the root partition on it.  I ended up rebooting (I don’t know how to get the boot to resume properly if I had managed to mount /root by hand.)

When that worked, I updated the Ubuntu partition’s /boot/grub/custom.cfg to use the UUID instead of the device path for Debian.

It seems that the kernel itself only supports partition UUIDs, but Debian and Ubuntu use initrds (initial RAM disks) that contain the code needed to find the filesystem UUID.  That’s why root=UUID={fs-uuid} has always worked for me!  Including this time.

os-prober (the original source of this entry) has to be more conservative, though, so it put root=/dev/sdb3 on the kernel command line instead.

The Unfixed Race

Sometimes, the wlan0 interface can’t be renamed to wlx{MAC_ADDRESS} because the device is busy.  I tried letting wlan0 be an alias in the configuration for the interface (using systemd-networkd) but it doesn’t seem to take.

I resort to simply rebooting if the login prompt doesn’t reset itself and show a DHCP IP address in the banner within a few seconds.

You have to admire the kernel and systemd teams’ dedication to taking a stable, functional process and replacing it with a complex and fragile mess.

A Brief Flirtation with X11

I installed Cinnamon.  It ran out of space; I ran apt clean and then continued, successfully.  This is my fault; I had “only” given the partition 8 GiB, because I expected it to be a CLI-only environment.

Cinnamon, however, is insistent on NetworkManager, and I was already using systemd-networkd.  It’s very weird to have the desktop showing that there is “no connection” while the internet is actually working fine.

Due to the space issue, I decided to uninstall everything and go back to a minimal CLI.  I would definitely not be able to perform another upgrade to Debian 13, for instance, and it was unclear if I would even be able to do normal updates.

In Conclusion

The Debian upgrade went surprisingly well, considering it was initially installed with debootstrap, and is therefore an unusual configuration.

Losing DNS might have been recoverable by editing /etc/resolv.conf instead, but I wasn’t really in a “fixing this from here is my only option” space.  Actually, one might wonder what happened to the DHCP-provided DNS server?  I don’t know, either.

Trying to add X11 to a partition never designed for it did not work out, but it was largely a whim anyway.

Sound for Firefox Flatpak on Ubuntu 23.04 with PipeWire

I reinstalled Ubuntu Studio recently, excised all Snaps, and installed Firefox from Flatpak.  Afterward, I didn’t have any audio output in Firefox.  Videos would just freeze.

I don’t know how much of this is fully necessary, but I quit Firefox, installed more PipeWire pieces, and maybe signed out and/or rebooted.

sudo apt install pipewire-audio pipewire-alsa

The pipewire-jack and pipewire-pulse packages were already installed.

AIUI, this means that “PipeWire exclusively owns the audio hardware” and provides ALSA, JACK, Pulse, and PipeWire interfaces into it.

It’s not perfect.  Thunderbird (also flatpak; I’d rather have “some” sandbox than “none”) makes a bit of cacophony when emails come in, but at least there’s sound for Firefox.

Boring Code Survives

Over on Wandering Thoughts, Chris writes about some fileserver management tools being fairly unchanged over time by changes to the environment.  There is a Python 2 to 3 conversion, and some changes when the disks being managed are no longer on iSCSI, “but in practice a lot of code really has carried on basically as-is.”

This is completely different than my experience with async/await in Python.  Async was new, so the library I used with it was in 0.x, and in 1.0, the authors inverted the entire control structure. Instead of being able to create an AWS client deep in the stack and return it upwards, clients could only be used as context managers.  It was quite a nasty surprise.

To allow testing for free, my code dynamically instantiated a module to “manage storage,” and whether that was AWS or in-memory was an implementation detail.  Suddenly, one of the clients couldn’t write self.client = c; return anymore.  The top-level had to know about the change.  Other storage clients would have to know about the change, to become context managers themselves, for no reason.

I held onto the 0.x version for a while, until the Python core team felt like “explicit event loop” was a mistake big enough that everyone’s code had to be broken.

Async had been hard to write in the first place, because so much example code out there was for the asyncio module’s decorators, which had preceded the actual async/await syntax.  What the difference between tasks and coroutines even was, and why one should choose one over the other, was never clear.  Why an explicit loop parameter should exist was especially unclear, but it was “best practice” to include it everywhere, so everyone did.  Then Python set it on fire.

(I never liked the Python packaging story, and pipenv didn’t solve it. To pipenv, every Python minor version is an incompatible version?)

I had a rewrite on my hands either way, so I went looking for something else to rewrite in, and v3 is in Go.  The other Python I was using in my VM build pipeline was replaced with a half-dozen lines of shell script.  It’s much less flexible, perhaps, but it’s clear and concise now.

In the end, it seems that boring code survives the changing seasons.  If you’re just making function calls and doing some regular expression work… there’s little that’s likely to change in that space.  If you’re coloring functions and people are inventing brand-new libraries in the space you’re working in, your code will find its environment altered much sooner.  The newer, fancier stuff is inherently closer to the fault-line of future shifts in the language semantics.

Installing Debian 12 and morrownr's Realtek driver (2023-07-03 edit)

Due to deepening dissatisfaction with Canonical, I replaced my Ubuntu Studio installation with Debian 12 “bookworm” recently.

tl;dr:

1. My backups, including the driver source, were compressed with lzip for reasons, but I fell back on a previously-built rescue partition to get the system online.
2. I ended up with an improper grub installation, that couldn’t find /boot/grub/i386-pc/normal.mod. I rebooted the install media in rescue mode, got a shell in the environment, verified the disk structure with fdisk -l, and then ran grub-install /dev/___ to fix it. Replace the blank with your device, but beware: using the wrong device may make the OS on it unbootable.
3. The USB doesn’t work directly with apt-cdrom to install more packages offline. I “got the ISO back” from dd if=/dev/sdd of=./bookworm.iso bs=1M count=4096 status=progress conv=fsync (1M * 4096 = 4G total, which is big enough for the 3.7G bookworm image; you may need to adjust to suit), then made it available with mount -o loop,ro ~+/bookworm.iso /media/cdrom0 (the mount point is the target of /media/cdrom.)
4. Once finished, I found out the DVD had plzip, and if I’d searched for it (lzip), I could have used it (plzip). I didn’t actually need the rescue partition.
5. Once finished, I realized I hadn’t needed to dd the ISO back from the USB stick. The downloaded ISO was on my external drive all along, and I could have loop-mounted that.
6. [Added 2023-07-02]: Letting the swap partition get formatted gave it a new UUID. Ultimately, I would need to update the recovery partition’s /etc/fstab with the new UUID, and follow up with update-initramfs -u to get the recovery partition working smoothly again.

Full, detailed rambling with too much context (as usual) below.

Passing data from AWS EventBridge Scheduler to Lambda

The documentation was lacking images, or even descriptions of some screens ("Choose Next. Choose Next.")  So, I ran a little experiment to test things out.

When creating a new scheduled event in AWS EventBridge Scheduler, then choosing AWS Lambda: Invoke, a field called "Input" will be available.  It's pre-filled with the value of {}, that is, an empty JSON object. This is the value that is passed to the event argument of the Lambda handler:

export async function handler(event, context) {
  // handle the event
}

With an event JSON of {"example":{"one":1,"two":2}}, the handler could read event.example.two to get its value, 2.

It appears that EventBridge Scheduler allows one complete control over this data, and the context argument is only filled with Lambda-related information.  Therefore, AWS provides the ability to include the <aws.scheduler.*> values in this JSON data, to be passed to Lambda (or ignored) as one sees fit, rather than imposing any constraints of its own on the data format.  (Sorry, no examples; I was only testing the basic features.)

Note that the handler example above is written with ES Modules.  This requires the Node 18.x runtime in Lambda, along with a filename of "index.mjs".

DejaDup and PikaBackup, early impressions (Update 2)

I tried a couple of backup programs:

• DejaDup (the one I had heard of), a front-end for Duplicity
• PikaBackup, a front-end for BorgBackup

I installed both of them as Flatpaks, although deja-dup also has a version in the Pop!_OS 22.04 repository.  I have been using DejaDup for four months, and PikaBackup for one month.  This has been long enough for DejaDup to make a second full backup, but not so long for Pika to do anything special.

Speed:

For a weekly incremental backup of my data set…

• DejaDup: about 5 minutes, lots of fan speed changes
• PikaBackup: about 1 minute, fans up the whole time

Part of Pika’s speed is probably the better exclusion rules; I can use patterns of **/node_modules and **/vendor, to exclude those folders, wherever they are in the tree.  With DejaDup, I would apparently have to add each one individually, and I did not want to bother, nor keep the list up-to-date over time.

Part of DejaDup’s slowness might be that it executes thousands of gpg calls as it works.  Watching with top, DejaDup is frequently running, and sometimes there’s a gpg process running with it.  Often, DejaDup is credited with much less than 100% of a single CPU core.

Features:

PikaBackup offers multiple backup configurations.  I keep my main backup as a weekly backup, on an external drive that’s only plugged in for the occasion. I was able to configure an additional hourly backup of my most-often-changed files in Pika.  (This goes into ~/.borg-fast, which I excluded from the weekly backups.) The hourly backups, covering about 2 GB of files, aren’t noticeable at all when using the system.

Noted under “speed,” PikaBackup offers better control of exclusions.  It tracks how long operations took, so I know that it has been exactly 53–57 seconds to make the incremental weekly backups.

On the other hand, Pika appears to always save the backup password.  DejaDup gives the user the option of whether it should be remembered.

There is a DejaDup plugin for Caja (the MATE file manager) in the OS repo, which may be interesting to MATE users.

Space Usage:

PikaBackup did the weekly backup on 2023-04-24 in 46 seconds; it reports a total backup size of 28 GB and 982 MB (0.959 GB = 3.4%) written out.

With scheduled backups, Pika offers control of the number of copies kept.  One can choose from a couple of presets, or provide custom settings.  Of note, these are count-based rather than time-based; if a laptop is only running for 8-9 hours a day, then 24 hourly backups will be able to provide up to 3 days back in time.

For unscheduled backups, it’s not clear that Pika offers any ‘cleanup’ options, because the cleanup is tied to the schedule in the UI.

I do not remember being given many options to control space usage in DejaDup.

Disaster Simulation:

To ensure backups were really encrypted, I rebooted into the OS Recovery environment and tried to access them.  Both programs’ CLI tools (duplicity and borgbackup) from the OS repository were able to verify the data sets. I don’t know what the stability guarantees are, but it’s nice that this worked in practice.

• duplicity verified the DejaDup backup in about 9m40s
• borgbackup verified the PikaBackup backup in 3m23s

This isn’t a benchmark at all; after a while, I got bored of duplicity being credited with 30% of 1 core CPU usage, and started the borgbackup task in parallel.

Both programs required the password to unlock the backup, because my login keychain isn’t available in this environment.

Curiously, borgbackup changed the permissions on a couple of files on the backup during the verification: the config and index files became owned by root.  This made it impossible to access the backups as my normal user, including to take a new one.  I needed to return to my admin user and set the ownership back to my limited account.  The error message made it clear an unexpected exception occurred, but wasn’t very useful beyond that.

Major limitations of this post:

My data set is a few GB, consisting mainly of git repos and related office documents.  The performance of other data sets is likely to vary.

I started running Pika about the same time that DejaDup wanted to make a second backup, so the full-backup date and number of incremental snapshots since should be fairly close to each other.  I expect this to make the verification times comparable.

I haven’t actually done any restores yet.

Final words:

Pika has become my primary backup method.  Together, its speed and its support for multiple configurations made hourly backups reasonable, without compromising the offline weekly backup.

Update History:

This post was updated on 2023-03-31, to add information about multiple backups to “Features,” and about BorgBackup’s file permission change during the verification test.  Links were added to the list above, and a new “Final Words” concluding section was written.

It was updated again on 2023-04-26, to add the “Space Usage” section, and to reduce “I will probably…” statements to reflect the final decisions made.