I’m exploring ways to shave a few seconds off of my boot time, and I came across a post that stated, “my initrd is pretty small–doesn’t really load much–and Arch also defaults to using zstd which is also faster to decompress versus gzip.”

What compression does Pop! use for initrd and the kernel? When I run ls -al /boot, I see files such as 14M vmlinuz-6.4.6-76060406-generic and 119M initrd.img-6.4.6-76060406-generic. Are these compressed?

Lastly, is there a way to choose the compression of these boot files without a custom kernel build? Or is what I’m trying to do “off the beaten path” and going to lead to “you have to compile your own kernel from here on out”?

  • TOR-anon1English
    1•1 year ago

    Then the kernel should be ztsd. Try running file and see the output.

    • @[email protected]OPEnglish
      1•1 year ago

      How would I check? Like this?

      $ zstd -l vmlinuz-6.4.6-76060406-generic 
Frames  Skips  Compressed  Uncompressed  Ratio  Check  Filename
File "vmlinuz-6.4.6-76060406-generic" not compressed by zstd
      • TOR-anon1English
        2•1 year ago

        No. Like this:

        file /boot/vmlinuz-6.4.6-76060406-generic
        • @[email protected]OPEnglish
          1•1 year ago

          Wow, this told me much more than I expected; however, I’m still not sure if it’s zstd:

          /boot/vmlinuz-6.4.6-76060406-generic: Linux kernel x86 boot executable bzImage, version 6.4.6-76060406-generic ([email protected]) #202307241739~1694621917~22.04~ac5e1a8 SMP PREEMPT_DYNAMIC Wed S, RO-rootFS, swap_dev 0XD, Normal VGA

          bzImage sounds like…bzip2, maybe?

          • TOR-anon1English
            1•1 year ago

            No. BZ stands for Big zImange. The kernel is compressed.

            To see what compression was used:

            zgrep CONFIG_KERNEL_ /proc/config.gz

            Try file on the initrd instead.

            • @[email protected]OPEnglish
              1•1 year ago

              Ah, thanks! Slightly different location, but basically the same. Here we go:

              $ grep CONFIG_KERNEL_ /boot/config-6.4.6-76060406-generic
# CONFIG_KERNEL_GZIP is not set
# CONFIG_KERNEL_BZIP2 is not set
# CONFIG_KERNEL_LZMA is not set
# CONFIG_KERNEL_XZ is not set
# CONFIG_KERNEL_LZO is not set
# CONFIG_KERNEL_LZ4 is not set
CONFIG_KERNEL_ZSTD=y

              So the kernel is “zstd” compressed.

              OTOH, I’m not sure if this means anything about initrd (ASCII cpio archive??)

              $ file /boot/initrd.img-6.4.6-76060406-generic 
/boot/initrd.img-6.4.6-76060406-generic: ASCII cpio archive (SVR4 with no CRC)
              • TOR-anon1English
                1•1 year ago

                Looks like your initrd isn’t compressed. Huh?