I’m troubleshooting /boot usage differences between Oracle Linux 8 systems that use different UEK kernel streams.
On some hosts, the initramfs images are gzip-compressed, while others produce uncompressed (ASCII cpio) images.
Example comparison:
# dncoem01 (UEK6)
$ file /boot/initramfs-*.img
/boot/initramfs-0-rescue-4a146c8447c2405cb136f774de6375bf.img: gzip compressed data, max compression, from Unix, original size 229616640
/boot/initramfs-4.18.0-553.79.1.el8_10.x86_64.img: gzip compressed data, max compression, from Unix, original size 63825408
/boot/initramfs-4.18.0-553.80.1.el8_10.x86_64.img: gzip compressed data, max compression, from Unix, original size 63824384
/boot/initramfs-5.4.17-2136.347.6.2.el8uek.x86_64.img: gzip compressed data, max compression, from Unix, original size 65954304
/boot/initramfs-5.4.17-2136.347.6.2.el8uek.x86_64kdump.img: ASCII cpio archive (SVR4 with no CRC)
/boot/initramfs-5.4.17-2136.348.3.el8uek.x86_64.img: gzip compressed data, max compression, from Unix, original size 65958912
/boot/initramfs-5.4.17-2136.348.3.el8uek.x86_64kdump.img: ASCII cpio archive (SVR4 with no CRC)
# dncai01 (UEK7)
$ file /boot/initramfs-*.img
/boot/initramfs-0-rescue-b2ba7236f71e47729d1c8d238158683c.img: ASCII cpio archive (SVR4 with no CRC)
/boot/initramfs-4.18.0-553.80.1.el8_10.x86_64.img: ASCII cpio archive (SVR4 with no CRC)
/boot/initramfs-5.15.0-313.189.5.1.el8uek.x86_64.img: ASCII cpio archive (SVR4 with no CRC)
/boot/initramfs-5.15.0-313.189.5.1.el8uek.x86_64kdump.img: ASCII cpio archive (SVR4 with no CRC)
Questions
- Where does dracut (as shipped with Oracle Linux UEK) determine its default compression method when no compress= is set?
- Did Oracle change that default between UEK6 (5.4.x) and UEK7 (5.15.x)?
- Is there a way to confirm definitively what the system’s default compressor is before running dracut (from a config or variable)?
Only thing I could find that could be applicable were these snippets
# dncoem01 (UEK6)
$ vi /usr/src/kernels/5.4.17-2136.348.3.el8uek.x86_64/include/config/auto.conf
CONFIG_HAVE_KERNEL_GZIP=y
CONFIG_KERNEL_GZIP=y
CONFIG_RD_GZIP=y
- # CONFIG_MODULE_COMPRESS is not set
CONFIG_DECOMPRESS_GZIP=y
# dncai01 (UEK7)
$ vi /usr/src/kernels/5.15.0-313.189.5.1.el8uek.x86_64/include/config/auto.conf
CONFIG_HAVE_KERNEL_GZIP=y
CONFIG_KERNEL_GZIP=y
CONFIG_RD_GZIP=y
+ CONFIG_MODULE_COMPRESS_NONE=y
+ # CONFIG_MODULE_COMPRESS_GZIP is not set
CONFIG_DECOMPRESS_GZIP=y
