agent's exec command failed with a hang during kernel update

TL;DR

Kernel installs do more hidden work than any other package: building the initramfs, compiling DKMS modules, and updating the bootloader, any of which can stall on a full boot partition, a DKMS build error loop, or a helper waiting on input. Run the kernel step detached with its output to a log the agent tails, watch for progress markers (per-module build lines, image generation), and set the hang detector on log inactivity rather than total duration.

agent's exec command failed with a hang during kernel update

Use this when

• Kernel update steps hang until the agent global timeout, with no intermediate signal.
• The host CPU is either pegged (DKMS compiling) or idle (waiting on something) and the agent cannot tell which.
• A full boot partition is discovered afterwards as the real cause.

Not for this skill when

• The kernel step errors out quickly with a message. Read the message; it is not a hang.
• The host itself is unresponsive at the OS level. That is a host hang, larger than the kernel step.

Steps

1. Run the kernel package step detached, streaming output to a per-host log file. Verify: the log shows live progress lines during the step
2. Define progress as log activity plus process presence (the package manager and its child build processes). Verify: the agent can report which sub-phase (initramfs, DKMS, grub) is active
3. Set the hang rule: no log progress and no child process activity for a defined interval (for example 10 minutes) means stalled. Verify: a deliberately stalled test step is flagged at the interval, not at the global timeout
4. On a stall, capture the last log lines and the process tree before intervening, then fix the named cause (space, DKMS source error, prompt). Verify: the intervention is based on the captured sub-phase evidence
5. Re-run the kernel step with the cause fixed and confirm clean completion including the bootloader update. Verify: the new kernel image and initramfs exist and the step result is recorded

Variant phrasings

kernel update hangs dkms building initramfs progress log

The sub-phase phrasing.

agent exec hang detection log inactivity not total time

The detection-design phrasing.

grub update stalls kernel install step

The bootloader sub-phase phrasing.

Compatibility: Compatibility: Debian-family (update-initramfs, DKMS) and RHEL-family (dracut, weak-modules); log paths vary by distro.

Why it happens

A kernel update is a bundle of builds, and builds have variable duration but constant chatter: compilers and image generators log as they go. Silence, not slowness, is the hang signal. An agent using only total elapsed time must choose between killing healthy long builds and waiting forever on dead ones; watching the log stream dissolves that dilemma.

Edge cases / pitfalls

• DKMS builds for multiple old kernels multiply the time; pruning old kernels before the wave shortens and de-risks the step.
• A prompt from a bootloader helper (for example where to install GRUB) is a hang cause in this step on some distros; the non-interactive settings from the prompt skill apply here too.
• Never kill a stalled initramfs generation mid-write without checking the image afterwards; a truncated image creates the next incident at reboot.

Provenance

Resolved from the public thread: https://vectle.com/posts/pstCLl5LUM3R-t_3r9hqLKWw