For some reason yaboot.conf was not copied to your Linux filesystem in /etc.
Let’s do it manually:
admin_user@Granny:/$ lsblk -o NAME,RM,RO,TYPE,SIZE,MODEL,FSTYPE,UUID,MOUNTPOINT,LABEL
NAME RM RO TYPE SIZE MODEL FSTYPE UUID MOUNTPOINT LABEL
sda 0 0 disk 74.5G ST380023A
├─sda1 0 0 part 31.5K
├─sda2 0 0 part 977K hfs bootstrap
├─sda3 0 0 part 1.9G swap cff9db76-66d9-4d7a-bafd-b741865fb941 [SWAP]
├─sda4 0 0 part 18.2G ext4 30cece28-a14f-4507-8758-8c189921e0da GRANNY-WILY
├─sda5 0 0 part 18.2G ext4 14812c6a-82be-499d-be75-212f4f4df82d / GRANNY-XENIAL
├─sda6 0 0 part 18.2G ext4 98b31bcd-7936-4d23-a28a-64f0b89594ba /Granny GRANNY
├─sda7 0 0 part 18.2G ext4 4160c897-0533-44b3-b3ec-203e6538d008 SPARE-2
└─sda8 0 0 part 24.5K
sr0 1 0 rom 1024M DVD-RW DVR-105
admin_user@Granny:/$ On my system, the HFS bootstrap is /dev/sda2.
admin_user@Granny:/$ sudo mount /dev/sda2 /mnt
[sudo] password for admin_user:
admin_user@Granny:/$ cd /mnt
admin_user@Granny:/mnt$ ls
ofboot.b yaboot yaboot.conf
admin_user@Granny:/mnt$ sudo cp yaboot.conf /etc
admin_user@Granny:/mnt$ cd ..
admin_user@Granny:/$ sudo umount /mnt
admin_user@Granny:/$It’s best not to keep the bootstrap partition mounted. Use “ybin” to update the yaboot
stuff in the bootstrap from /etc/yaboot.conf.