Arch Linux Install, Why is arch-chroot giving me an error?
/sys is a virtual file system that interfaces with the kernel. It is meant to replace /proc. More at https://en.wikipedia.org/wiki/Sysfs
By the sounds of it, you have /mnt/sys mounted, try umount /mnt/sys or better yet, reboot. If it is doing this after the reboot, then arch-chroot is probably has a typo, mount /sys /mnt/sys should be mount --bind /mnt/sys. I could potentially help more if you could post the output of mount. Not sure if you have figured the solution out, as you posted it nearly a month ago.