[arch-projects] [mkinitcpio] lz4 support

Jason St. John jstjohn at purdue.edu
Fri Dec 20 21:38:57 EST 2013

On Fri, Dec 20, 2013 at 1:20 AM, Dave Reisner <d at falconindy.com> wrote:
> On Fri, Dec 20, 2013 at 02:58:36AM +0000, Chris Rule wrote:
>> Hi, sorry in advance if I haven't reported this correctly. I was hesitant to
>> file a bug report until I was sure it is a bug, and what the bug was in.
>> I just tested lz4 compression with mkinitcpio after noticing it in the
>> conf.pacnew.
>> When I rebooted I got the following error after grub and my computer froze:
>> [0.<cut>] Initramfs unpacking failed: junk in compressed archive
> ...
>> [0.<cut>] Kernel panic - not syncing: VFS: Unable to mount root fs on
> <snip>
>> 1) I first found the messages to the linux kernel mailing list adding support
>> for lz4 to the kernel, describing it for arm and x86 so I initially assumed lz4
>> compressed images weren't supported with x86_64.
> x86_64 is still x86.
>> 2) I then read the thread (https://code.google.com/p/lz4/issues/detail?id=83)
>> linked from the lz4 commit in the mkinitcpio git repository (https://
>> projects.archlinux.org/mkinitcpio.git/commit/?id=
>> b5927393d103af9b8b2da80e8636b8aa52f80755), although I'm not sure I understood
>> everything in that thread I wonder if it may be a bug in lsinitcpio.
> lsinitcpio is irrelevant for booting (it's just an analysis/debugging
> tool). Anyways, it's just calling the lz4 binary, same as mkinitcpio.
>> 3) grub has "insmod gzio" in grub.cfg for all arch menu entries and looking at
>> gzio on the grub git it states it is for gzip decompression. I also found
>> lzopio.mod in /usr/lib/grub/i386-pc and /usr/lib/grub/x86_64-efi, though I
>> can't find any description for it I wonder if grub needs another module for
>> decompressing the lz4 ramdisk.
> Your bootloader is NOT responsible for decompressing the initramfs. The
> first line of your kernel output shows the *kernel* failing to unpack
> the initramfs.
>> Has a lz4 compressed ramdisk worked for anyone else and if it has can you help
>> me rule out any of these options or does anyone think I missed something?
> Nope, but this isn't likely to be a bug in mkinitcpio (unless I'm
> missing some magical flag, such as --check=crc32 being needed for xz).
> I'd talk to lz4 upstream if you want this resolved.
> d

I had the same problem as Chris with a VirtualBox VM running Arch. I
was able to replicate the same kernel panic on two other,
non-virtualized Arch machines I use.

All three Arch systems are running 3.12.5-1-ARCH (the standard Arch
kernel from [core]) with mkinitcpio-16, and the kernel panic occurs
after switching from lzop to lz4.

Dave, do you have anything in COMPRESSION_OPTIONS in your
/etc/mkinitcpio.conf (assuming you are using lz4)?

I have reported this on the lz4 issue tracker here:


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