I succesfully installed Slax 7 on my HDD using the ./bootinst.sh command then, on boot, the system was unable to boot from the HDD. I found that when this error occurs, it is needed to change the SYSLINUX bootloader with another version (don’t know why).
I tried the one suggested in the other post and it worked fine.
To install the bootloader we’ll use the extlinux utility (the synopsis says that it works on ext2 / ext3 filesystems, I was on an ext2 fs).
Download syslinux-4.06.tar.gz and bring it into a newly created folder of the hdd. Then
tar xvf syslinux-4.06.tar.gz cd syslinux-4.06/extlinux ./extlinux --install /media/system/slax/boot/
Remember that my hdd was labelled “system” and (automatically) mounted on /media/system/