A Sony Mebius here with antiX on a CF card.

Menu: Logout > Shutdown
and Logout > Reboot
each gives, within a few seconds, an almost black screen
with the fan still running. The system never shuts down
properly.

<Ctrl>+<Alt>+<F1> gives the same almost black screen with
the fan running. No command prompt.

If the power button is immediately pressed and held for
about 5 seconds, the fan stops and the screen becomes
absolutely black.

After booting again,
"ANTIX was not cleanly unmounted, check forced."
After fscking manually and fixing, the the system runs again.

On shutdown, I can wait about ten seconds before holding the
power button. When booting again, the"ANTIX was not cleanly
unmounted" message appears but the automated fsck passes and
manual fsck is not required and soon the system is running
again.

This is not an NTFS or FAT FS problem. The CF has ext2 file
systems. /, /home and swap appear in fstab according to UUID.

Yes, I googled. Nothing really relevant. Ideas?

Thanks, ... Peter E.

$ sudo halt -p

df showed that / was 100% used, which it shouldn't
have been. Also, some routinely used commands
weren't available. File system was corrupted?

Reinstalling antiX yielded a working system. Again
I'll add a / etc/X11/xorg.conf.d/xorg.conf and see
whether antiX and X work on the Sharp Mebius.

# / etc/X11/xorg.conf.d/xorg.conf
Section"Device"
Identifier"Device0"
Driver"vesa"
EndSection

Section"Screen"
Identifier"Screen0"
Monitor"Monitor0"
Device"Device0"
EndSection

The preceeding is independent of any
/ etc/X11/xorg.conf.

Regards, ... Peter E.