Cinnamon with Accelerated Graphics in libvirt

While exploring virt-manager and Linux Mint Cinnamon Edition, I kept getting the warning that software rendering was in use (instead of hardware acceleration.) The warning asks to open the Driver Manager, which then says no drivers are needed.

The open-source stack for doing accelerated graphics in this case is SPICE, but virt-manager had configured a different graphics stack by default for the “Ubuntu 20.04” OS setting I had used.

For the guest to use SPICE, it needed the spice-vdagent package to be installed.  After that, the guest was shut down, so that its hardware could be reconfigured.

First, the “video” element needed to be converted from QXL to virtio driver, which includes a 3D acceleration option.  Once the latter option’s checkbox was ticked, I clicked Apply to save the configuration.

Next, the “display” needed to be changed to support direct OpenGL rendering. I needed to change the Listen to none, and to tick the OpenGL checkbox. (Doing this in the opposite order, an “invalid settings” message appeared, saying that OpenGL is not supported unless Listen is none.) This revealed an option to select a graphics device, but I only have one, so I left it alone. I then applied the display changes.

Finally, I booted the guest again.  Everything seems to have worked, and the warning did not appear.

Fun with Linux I/O Stats

A discussion with my wife about random I/O and how I’m not sure NVMe would make a measurable difference to my life got me to wondering, how much I/O does a modern Linux system perform during bootup?

I have Ubuntu Studio 21.04 installed on hardware, and it issues around 18,800 read requests for 1.5 million sectors to boot to the desktop (and to start Alacritty to cat /proc/diskstats.)

I then installed Linux Mint 20.2 Cinnamon Edition and Xubuntu 21.04 in virtual machines, and ran similar tests, using their native terminal emulators.  Mint issues around 19,000 read requests for 1.2 million sectors.

Xubuntu issues about 20,500 read requests for 1.4 million sectors.

To be fair, Xubuntu does win the “least RAM used” contest.  After checking the diskstats file, free -m indicated 428 MB in use on Xubuntu, 547 MB on Mint Cinnamon, and 637 MB on Ubuntu Studio.

Xubuntu was a surprising disappointment; besides issuing the most read requests to boot up, it lacked in features.  The keyboard layout wouldn’t work.  I also discovered along the way that its live environment can’t control the backlight on a “late 2012” iMac, unlike mainline Ubuntu.

(Originally, I was hoping to get the info from the live environment, but the automatic media check dashed my hopes.)

Based on the information so far, I don’t have any new evidence that NVMe would be much of a performance boost.  Sure, the numbers are bigger, but I’m looking for a life-altering wow factor, like going from HDD to SSD was.

Added 2021-07-29: Synthetic benchmarks don’t seem to add up to real-world performance.  (As usual!) It makes great gains in CrystalDiskMark, but actual tasks can turn game load times from 36 to 30 seconds, or a 1.8 GB Photoshop file from 18 to 11 seconds.  To be fair, that seems to be on the order of magnitude of Linux booting up, which I’m largely interested in as the most massive task I tend to put my hardware to.  It’s not like the SATA SSD is so slow that my mind wanders while waiting for Firefox to load.

For something that’s marketed as if it’s five to ten times faster, that’s a disappointingly weak effect in practice.  And worse, a PCIe 4.0 drive can cost more than double of what the SATA variant does, with the same manufacturer and capacity.  For that kind of money, I want the performance to double across the board.  But I’m getting older, wiser, and grumpier.

What is @system-service?

Because it's subject to change, systemd does not officially publish what makes up "@system-service".  However, as of June 20th, 2021, the git repository defines the system calls allowed in src/shared/seccomp-util.c.  In addition to some more calls, @system-service (SYSCALL_FILTER_SET_SYSTEM_SERVICE) currently includes the following groups:

@aio, @basic-io, @chown, @default, @file-system, @io-event, @ipc, @keyring, @memlock, @network-io, @process, @resources, @setuid, @signal, @sync, and @timer.

It may be more interesting to consider what it doesn't include:

@clock, @cpu-emulation, @debug, @module, @mount, @obsolete, @pkey, @privileged, @raw-io, @reboot, and @swap.

This is not a list of what it "excludes," because system calls may appear on multiple lists; "chown" is permitted by @chown, and the non-inclusion of @privileged doesn't revoke that permission.

Some further observations:

• @aio includes io_uring.
• @raw-io is port-based I/O, and configuration of PCI MMIO.
• @basic-io is read/write and related calls; @file-system is a much larger group that covers access, stat, chdir, open, and so on.
• @io-event is evented I/O, that is, select/poll/epoll.

Essentially, @system-service is meant to permit a fairly wide range of operations.  This makes it easier to start using (less likely to break things), at the cost of potentially leaving the gates open more than necessary.

As for my own systems, I may start revoking @privileged and @memlock from daemons that run as a non-root user from the start.  Other than that, this exercise didn't turn out to be very informative.

Update on 2021-06-25: The command systemd-analyze syscall-filter will show all of the built-in sets; systemd-analyze syscall-filter @privileged will show the filters for a specific set (in this example, the "@privileged" list of calls.)

aws-vault on macOS Catalina

I recently installed aws-vault on my old iMac, for malware hardening.  If any finds me, I don’t want it to be able to pick up ~/.aws/credentials and start mining cryptocurrency.

One problem: there were a lot of password prompts, and the “aws-vault” keychain did not appear in Keychain Access as promised.

But it’s okay; there’s a security command that works with it, if we know the secret internal name of the keychain: aws-vault.keychain-db.  (I found this by looking in my ~/Library directory for the keychains; most of them have several files, but aws-vault has only that one.)

As in:

1. security show-keychain-info aws-vault.keychain-db
2. security set-keychain-settings -l -u -t 900 aws-vault.keychain-db
3. security lock-keychain aws-vault.keychain-db
4. security set-keychain-password aws-vault.keychain-db (this will prompt for current and new passwords)

Regarding the set-keychain-settings subcommand.  Each option specifies a setting: -l to lock the keychain whenever the screen is locked, -u to lock the keychain after a time period, and -t {seconds} to set that time period. So, in the example, we are setting the keychain to lock again after 900 seconds.  There do not seem to be opposites of these options documented, so I would guess running the command without a flag will remove that option.  I haven’t tested that, though.

I added the lock-keychain subcommand to my logout file [~/.zlogout for zsh, but formerly ~/.bash_logout].  Whenever I exit an iTerm2 tab, everything is locked again.  (I’ve been clearing SSH keys from the agent in that file for a long time.)

I’ve chosen to “Always Allow” aws-vault to access the keychain, which means I need to put in the password only for the unlocking operation, not for every time the binary wants to access information within the keychain.

I Don't Know What Grub2 Is Doing

Background: there are a couple of things I do that are far more convenient on Linux, so I decided to replace the USB stick I was using with an SSD.  I bought and installed the SSD, installed Ubuntu Studio 20.10, and let it install Grub to /dev/sda.  Big mistake.

Windows could not be booted.  I wiped the Linux SSD, and then nothing booted; Grub expected to find itself on that drive.  Booting the Linux installer from the USB stick would detect the ghost of Grub in the MBR, and jump into it, instead of starting the stick.  I had to pull out an old copy of SysRescueCd to put something else in Windows' MBR.

But at that point, Windows would still not boot, nor would it repair itself from the repair mode.  I ended up having to reinstall Windows through an unnecessarily confusing and pointless set of menus on the install media.  That's not what the story is about, though.

With a functional Windows on /dev/sda, I reinstalled Linux again, and told it to put the boot loader on /dev/sdb.  This works fine, with the little weird problem that Grub still can't boot Windows 10?

I haven't gone through and tried set root=(hd0) and chain-loading that, but you know, this is 2021? This should work out of the box.

Despite having a "Dual UEFI BIOS" on my motherboard, it boots Windows in legacy/BIOS mode, and not UEFI mode.  So it's not a case of Linux being booted with legacy/BIOS, then not realizing that it needed grub-efi.  I think.

At some level, I don't care.  If it doesn't work, it doesn't work.  The PC is now configured to boot Windows by default, or Linux when I ask for a boot menu and pick the second SSD.  And I'm really just grumpy that the installer/Grub can't figure out how to get Windows up and running properly.

The libsodium rant

Back when the inclusion of libsodium in PHP 7.2 was announced, I was excited.  A modern crypto library, with a modern, easy-to-use API?  Unfortunately, calling the API "modern" meant something completely different to me than the libsodium binding actually delivers to its users.

Rather than a modern, mistake-proof API, it's a direct, low-level replacement for the unmaintained mcrypt library.  It has more modern primitives, obscure names, and very little documentation.  Although the extension was promoted to core years ago, the functions are all "Warning: this is undocumented" to this day.  (Extension documentation is here.)

As for the names, I actually attended a libsodium talk at a PHP conference.  The speaker covered which functions are asymmetric and which are symmetric, but I don't remember which is which without checking my notes.  The docs say "Encrypt a message" for sodium_crypto_box, sodium_crypto_box_seal, and sodium_crypto_secretbox.  They also say that about sodium_crypto_stream_xor, but that definitely sounds wrong.

I had been expecting an interface more like defuse/php-encryption (which I have used) or perhaps soatok/dhole-cryptography (which I have not.)  Even if all the low-level crypto bits were exposed, because interoperability with other systems is important, I still expected a higher level API.  I expected an "encrypt this text with that key" operation that took care of nonces, formatting details, and algorithm choices.

The sea change to vendoring and containers

Not so long ago, we would install code to the global runtime path, where it would be available machine-wide.  CPAN was perhaps the earliest to do this, but PEAR, rubygems, and probably others followed.  After all, CPAN was seen as a great strength of Perl.

Users of such a library would say something like use Image::EXIF; or include_once "Smarty/Smarty.class.php"; Notice that these are a mechanism to follow some include path to resolve relative filenames.

But as servers got larger faster than applications, co-installing those applications became attractive.  The problem was that they can have different dependency requirements, which complicates the management of a shared include path.

This is about where Bundler happened for Ruby, and its ideas were brought to other ecosystems: Perl got carton, and PHP got composer. These systems build a directory within the project to hold the dependencies, and basically ignore the global include path entirely.

At the cost of disk space, this bypasses the problems of sharing dependencies between projects.  It bypasses all the problems of working with multiple versions of dependencies that may be installed in different hosts’ include paths.  It also makes the concept of the language’s include path obsolete, at least in PHP’s case: the Composer autoloader is a more-capable “include path” written in code.  Finally, it allows piecemeal upgrades—a small service can make a risky upgrade and gain experience, before a larger or more important service on the machine needs to upgrade.

Piecemeal upgrades also enable independent teams to make more decisions on their own.  Since their dependencies are not shared with other users, changes to them do not have to be coordinated with other users.

Containers are the next step in the evolution of this process.  Pulling even more dependencies into a container brings all the advantages of local management of packages into a broader scope.  It allows piecemeal upgrading of entire PHP versions.  And it makes an application cost an order of magnitude more space, once again.

In our non-containerized environment, I can switch the PHP version on a host pretty easily, using co-installable versions and either update-alternatives (for the CLI) or a2disconf/a2enconf (for FPM), but this means the services do not really have a choice about their PHP version.  It has been made before the application's entry point is reached.