Grub with Fastboot not working

DASK

Dual booting with win7 and since the last update on a soft reboot grub menu never appears and the system boots direct to solus. On a cold start grub appears and works fine.

I turned off fast boot in the bios and that seems to have fixed the issue but it was working fine with fastboot on for the last year of install. Any idea what might have changed ?

gohlip

If booted to linux and then rebooted, fastboot will not affect it. That's why you will not have a problem when reboot from linux. If on windows, you reboot, fastboot will by its function like hibernation, will store some data at shutdown; and that will affect linux startup from a windows shutdown.
Nothing changed. And nothing to do with grub.

You will also need to watch out for hiberfile in windows, not just fastboot.
Disabling hiberfile will also disable fastboot.

DASK

The problem is a reboot from linux to windows, not windows to linux. I disabled hiberfile.sys years ago in win7 to save space since I do not need hibernation.

Just turned fastboot back on to confirm. Cold boot to win7 fine. Reboot and grub appears so boot to solus. Reboot again and grub never appears and system just boots back to solus unless I power off. I can disable fastboot for now.

gohlip

DASK . Reboot again and grub never appears and system just boots back to solus unless I power off.

Let's take a look at your /etc/default/grub and grubenv

cat /etc/default/grub
grub-editenv list

Maybe something's not right there.
You probably have grubdefault but not turned on grubsavedefault
With solus, probably best to disable both.

DASK

GRUB_DEFAULT=0
GRUB_TIMEOUT=10
GRUB_DISTRIBUTOR=lsb_release -i -s 2> /dev/null || echo Solus
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
GRUB_CMDLINE_LINUX=""
GRUB_BACKGROUND=""
GRUB_COLOR_NORMAL="black/white"
GRUB_COLOR_HIGHLIGHT="light-blue/white"
GRUB_HIDDEN_TIMEOUT_QUIET=false

I think I might have solved my own problem. It seemed that the grub timeout had defaulted back to 5s from my modified 10s. When rebooting from win7 the reboot process is fast so grub always appeared within the 5s. But for some odd reason when rebooting from solus the reboot process is different (no idea why) and my monitor temporary goes into power save mode for a split second or 2. Then when it comes back on the timing is just at that exact moment solus boot has been selected by default so I never see grub but the initial boot process in terminal. Fluke timing.

gohlip

GRUB_HIDDEN_TIMEOUT_QUIET=false

is deprecated. Comment that out.
Add one line.
GRUB_TIMEOUT_STYLE=menu
save file
Then do

sudo update-grub

You should be fine.

ps: Not important to your issue, but see if you have a picture file "/usr/share/backgrounds/splash.tga"
Then change to
GRUB_BACKGROUND="/usr/share/backgrounds/splash.tga"
Just looks nicer.