busybox-initramfs: modinfo reports "can't open '/${VERSION}/': No such file or directory"

[TJ]

Working on 16.04 and trying to solve some unrelated issues due to a complex initrd set-up I discovered that the included "modinfo" tool doesn't work, whether given just a module name or an absolute path to the .ko file.

In this case it always reports, e.g:

(initramfs) pwd
/lib/modules/4.4.0-21-generic/kernel/drivers/md

(initramfs) modinfo dm-crypt
modinfo: can't open '/4.4.0-21-generic/': No such file or directory

(initramfs) modinfo /lib/modules/4.4.0-21-generic/kernel/drivers/md/dm-crypt.ko
modinfo: can't open '/4.4.0-21-generic/': No such file or directory

There seems there may be a related issue with modprobe too, as I've found it doesn't always insert a module when instructed to - also using either just name, or absolute path. In the specific case here I was working with a LUKS/dm-crypt rootfs, where the initrd.img had been generated using "MODULES=dep" and hadn't included dm-crypt.ko.

I connected a USB storage device with an identical root file-system (same kernel version, etc.) at /mnt/USB/ and was trying to use:

(initramfs) modprobe -v -d /mnt/USB dm-crypt
modprobe: FATAL: Module dm-crypt not found in directory /mnt/USB/lib/modules/4.4.0-21-generic

I'm *assuming* this is because despite setting the alternate root directory with "-d" it is still looking at the "modules.dep" in /lib/modules/4.4.0-21-generic rather than prefixing the "-d" alternate root.

Using a chroot the module(s) can be loaded and the block device unlocked:

(initramfs) chroot /mnt/USB
(initramfs) modprobe dm-crypt
(initramfs) modprobe aesni-intel
(initramfs) modprobe xts
(initramfs) exit
(initramfs) grep dm_crypt /proc/modules
dm_crypt 28672 0 - Live 0xffffffffc02fa000

(initramfs) LD_LIBRARY_PATH=/mnt/USB/lib/x86_64-gnu-linux /mnt/USB/sbin/cryptsetup open /dev/sda4 LUKS_VG02 --type luks

(initramfs) blkid /dev/mapper/LUKS_VG02
/dev/mapper/LUKS_VG02: UUID="xxxx...xxxx" TYPE="LVM2_member"

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Diederick Niehorster (dcnie)]

I'm also affected by this bug, on 18.04.2, can't open /4.18.0-20-generic/

[Shane Thompson (shanept)]

I am also affected. Additionally I can not get any stderr output from modprobe, whether I use -v or not.