UPDATE: Additional facts on trigger-path theory My 2026-08-05 comment suggested kernel-triggered DKMS builds (dkms autoinstall) come out uncompressed while driver-only package upgrades (dkms build/dkms install) come out compressed. Further testing (two machines, both AMD/Nvidia) shows that theory was incomplete — kernel- triggered builds can produce compressed output too. Here's the underlying mechanism, confirmed by reading /usr/sbin/dkms (3.0.11-1ubuntu13) and comparing apt logs across two kernel installs.
DKMS doesn't read CONFIG_MODULE_COMPRESS_ZSTD from the kernel config. At build time it checks whether the target kernel's /lib/modules/<kernel>/modules.dep already has .zst entries, and mirrors that compression for its own output: # /usr/sbin/dkms, lines 223-225 grep -q '\.zst:' /lib/modules/$kernel_test/modules.dep 2>/dev/null && module_compressed_suffix=".zst" modules.dep reads .zst entries from depmod, run by linux- modules-<kernel>/linux-image-<kernel>'s postinst. DKMS itself runs from linux-headers-<kernel>'s postinst (/etc/kernel/header_postinst.d/dkms). Whether DKMS sees those entries depends on whether linux-modules/linux- image were configured by dpkg *before* linux-headers — and that order isn't fixed across apt transactions. So, while the previous investigation seemed that just driver-only upgrades were affected, in fact, it can be kernel-triggered upgrades as well; it is just a timing issue as noted. Log comparison on the same machine shows the flip directly: Kernel 7.0.0-30-generic (2026-08-24, uncompressed — no bug): Setting up linux-headers-7.0.0-30-generic ... /etc/kernel/header_postinst.d/dkms: <- DKMS checks modules.dep here Setting up linux-modules-7.0.0-30-generic ... <- depmod runs after Kernel 7.0.0-31-generic (2026-09-03, compressed — bug reproduced): Setting up linux-modules-7.0.0-31-generic ... <- depmod runs first Setting up linux-headers-7.0.0-31-generic ... /etc/kernel/header_postinst.d/dkms: <- DKMS checks modules.dep here, finds .zst Same dkms version, same nvidia driver version, same kernel config, same machine — only the dpkg configuration order differed. -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/2154307 Title: DKMS modules installed as .ko.zst; are not included in initramfs To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/initramfs-tools/+bug/2154307/+subscriptions -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
