Hi: I created partition 6 and moved slackware 14.0-32, which was in partition 1 to partition 6. Then I modified lilo.conf and fstab and ran lilo. Maybe I modified the fstab that was in 1 instead of that of 6, do not remember well. When I booted slackware everything went well. Then I deleted partition 1 and booted again. But this time, during booting, I got the message in the thread title followed by "ERROR: No /sbin/init found on rootdev (or not mounted). Trouble ahead. You can try to fix it. Type 'exit' when things are done". And was given a prompt.

Now, why is the system trying to mount /dev/sda1? I can't understand. How does it know the O.S. was in /dev/sda1 before?

Because you still told to mount /dev/sda1 on / in the /etc/fstab found on your new root file system (mounted on /dev/sda6), as this is not the file that you have edited. So the system looks for /sbin/init on /dev/sda1 but when it does so /dev/sda1 is not yet mounted.

So no, the system doesn't not "know" that /dev/sda1 was the old root device, it just reads /etc/fstab to know what the root device is, as it should.

But in sda6/etc/fstab I tell it it's sda6! The /etc/fstab in sda6 now says:

/dev/sda6 / ext2 defaults 1 1

I don't know how to make the system forget about sda1!

That would mean that the lilo stanza you use still has

Apparently. But I ran lilo with boot=/dev/sda6 and root=/dev/sda6.

All of a sudden I understood what is happening. When linux was in sda1 the boot loader was in the MBR (disk absolute sector 0). I had root=/dev/sda in lilo.conf. Then I move it to sda6 and changed that line to root=/dev/sda6. But BIOS was still loading the boot loader from the MBR! What I did now is to run lilo with the old line root=/dev/sda and the system boot OK.

However, the only way I had found to be able to boot windows 7, which I have in partitions 2 and 3, was to have root=/dev/sda6 (root=/dev/sda1 before moving linux). With root=/dev/sda I get "bootmgr is missing" when booting win 7.

I'm confused. Do you mean root= or boot= above? Cause according to the man page it's boot= that says where to put the boot loader and root= is just a way to pass along the kernel command line parameter of that name to linux.

I had linux in sda1 and boot=/dev/sda (sic). Then I installed windows 7 and couldn't make lilo boot it until I happened to put boot=/dev/sda1. Then I created partition 6 and moved linux to it, with boot still equal boot=/dev/sda6. And here is where I got "mount: mounting /dev/sda1 on /mnt failed" at boot time and could boot linux no longer. Then I put boot=/dev/sda and I could boot well. That's all I can say. Of course root= was modified where appropriate.

EDIT: my mistake. In post #6 it should say 'boot=' and not 'root='.