22 Jan
2020
22 Jan
'20
2:13 p.m.
Hi,
TL;DR: The HWE kernel on 64-bit Ubuntu 18.04 does seem to work and
does not use LZ4 compression for its initramfs - it's still gzip.
I've just installed Ubuntu 18.04 64-bit and then installed
linux-generic-hwe-18.04 which gets me:
$ ls -la /boot/*5.3*
-rw-r--r-- 1 root root 235811 Dec 18 15:01 /boot/config-5.3.0-26-generic
-rw-r--r-- 1 root root 65897765 Jan 22 13:39 /boot/initrd.img-5.3.0-26-generic
-rw------- 1 root root 4487587 Dec 18 15:01 /boot/System.map-5.3.0-26-generic
-rw------- 1 root root 9146616 Dec 18 15:20 /boot/vmlinuz-5.3.0-26-generic
This does boot 64-bit and I don't believe it's using LZ4 compression for
anything:
$ grep COMPRESS /etc/initramfs-tools/initramfs.conf
# COMPRESS: [ gzip | bzip2 | lzma | lzop | xz ]
COMPRESS=gzip
Though "file" can't seem to tell what it is:
$ file /boot/initrd.img-*
/boot/initrd.img-4.15.0-74-generic: ASCII cpio archive (SVR4 with no CRC)
/boot/initrd.img-5.3.0-26-generic: ASCII cpio archive (SVR4 with no CRC)
I think this is because the first bit of the initramfs is an
uncompressed cpio containing a CPU microcode update:
$ cpio -ivt < /boot/initrd.img-5.3.0-26-generic
drwxr-xr-x 3 root root 0 Nov 28 2018 .
drwxr-xr-x 3 root root 0 Nov 28 2018 kernel
drwxr-xr-x 3 root root 0 Nov 28 2018 kernel/x86
drwxr-xr-x 2 root root 0 Nov 28 2018 kernel/x86/microcode
-rw-r--r-- 1 root root 30546 Nov 28 2018
kernel/x86/microcode/AuthenticAMD.bin
62 blocks
This uncompressed cpio blob can be stripped by skipping 62 blocks as
noted above:
$ dd if=/boot/initrd.img-5.3.0-26-generic of=/tmp/initrd.img bs=512 skip=62
128644+1 records in
128644+1 records out
65866021 bytes (66 MB, 63 MiB) copied, 0.715398 s, 92.1 MB/s
But then:
$ file /tmp/initrd.img
/tmp/initrd.img: ASCII cpio archive (SVR4 with no CRC)
$ cpio -ivt < /tmp/initrd.img
drwxr-xr-x 2 root root 0 Oct 15 13:00 kernel
drwxr-xr-x 2 root root 0 Oct 15 13:00 kernel/x86
drwxr-xr-x 2 root root 0 Oct 15 13:00 kernel/x86/microcode
drwxr-xr-x 2 root root 0 Oct 15 13:00
kernel/x86/microcode/.enuineIntel.align.0123456789abc
-rw-r--r-- 1 root root 2960384 Oct 15 13:00
kernel/x86/microcode/GenuineIntel.bin
5784 blocks
So that's another uncompressed cpio blob. Looks like first is AMD
microcode and second is Intel microcode. Okay so try stripping both
(5784+62=5846 blocks):
$ dd if=/boot/initrd.img-5.3.0-26-generic of=/tmp/initrd.img bs=512 skip=5846
122860+1 records in
122860+1 records out
62904613 bytes (63 MB, 60 MiB) copied, 0.793158 s, 79.3 MB/s
$ file /tmp/initrd.img
/tmp/initrd.img: gzip compressed data, last modified: Wed Jan 22 13:39:21 2020, from Unix
Well alrighty then…
$ zcat /tmp/initrd.img | cpio -ivt | head
drwxr-xr-x 12 root root 0 Jan 22 13:39 .
-rwxr-xr-x 1 root root 6682 Oct 7 11:53 init
drwxr-xr-x 4 root root 0 Jan 22 13:39 usr
drwxr-xr-x 3 root root 0 Jan 22 13:39 usr/share
drwxr-xr-x 3 root root 0 Jan 22 13:39 usr/share/plymouth
drwxr-xr-x 4 root root 0 Jan 22 13:39 usr/share/plymouth/themes
drwxr-xr-x 2 root root 0 Jan 22 13:32
usr/share/plymouth/themes/ubuntu-text
-rw-r--r-- 1 root root 209 Apr 4 2019
usr/share/plymouth/themes/ubuntu-text/ubuntu-text.plymouth.in
-rw-r--r-- 1 root root 205 Jan 22 13:32
usr/share/plymouth/themes/ubuntu-text/ubuntu-text.plymouth
lrwxrwxrwx 1 root root 59 Jan 22 13:39
usr/share/plymouth/themes/text.plymouth ->
/usr/share/plymouth/themes/ubuntu-text/ubuntu-text.plymouth
"lsinitramfs" should do all this much simpler but I couldn't find a
way to have it tell me which decompression method it was using. If
you do know a simpler way of telling then please do let me know!
I will now reinstall that using 32-bit to verify that it does not
work.
Cheers,
Andy
--
https://bitfolk.com/ -- No-nonsense VPS hosting