Filesystem layout with sperated /boot partition

Jerry McAllister jerrymc at
Mon Apr 3 15:03:53 UTC 2006

> Hello FreeBSD Fans,
> I wanted to create a new system and was thinking about the following layout.

Do you really mean that or to you mean put "root" which is '/' in its
own partition?   

There is no reason to put just /boot in a separate partition. It's just 
a directory to help keep some things nicely organized and has no real 
stand-alone value.  It is not very large nor does anything write to it 
in ways that might make it change size in an uncontrolled manner.  Those
things (size, stand-alone value, may grow in size unexpectedly) are the
usual reasons for making a separate partition plus isolating users and

> Size | Mountpoint | Device name | File system
> 100M /boot /dev/ad2s1a UFS2+S
> 1024MB --- /dev/ad2s1b SWAP
> 15GB / /dev/ad2s1c UFS2
> I want to put /boot on its own partition, but somehow I dont have a lot of luck.
> I can install the OS, but when I reboot the bootloader will not boot.
> No /boot/loader
> ...
> Default: 0:ad(0,a)/boot/kernel/kernel
> boot:
> No /boot/kernel/kernel
> ...
> 1) I wouldnt mind on which partition "/boot" or "/" sits or what its named, 
> but I would like to separate "/boot" on a different partition and it seems 
> like it wouldnt boot when I do this. Is this just a matter of updating the 
> bootloader ?   Wouldnt the installer do that automatically ?

The reason it won't boot that way is that everything needed to boot must 
be in the booting partition because nothing else is mounted at that time.
The boot partition must be 'a' and must be montable as '/' (usually called 
root).   During boot, the system does a special read-only mount of the 
first ('a') partiton in the bootable slice.   /boot is supposed to be part 
of that partition.   If you make /boot a separate partition, then it will 
not be mounted and not be available for the boot process to read.  Since 
there is stuff in there that is needed for boot, then it won't work.

Anyway, when the system comes up to a full multi-user mode, it mounts 
everything as in /etc/fstab.   That first (a) partition then is remounted 
according to what is given in /etc/fstab which must be '/' (eg root) for 
things to work right and is normally mounted read/write (though there are 
ways of arranging things to make it work read only).   

I am guessing you don't understand the meaning of what is in /boot and 
what it is used for.  See first part of my comments.

Maybe /boot is an unfortunate name for that directory.  Maybe it should
really be named kernel.stuff or kernel.loader or something like that.  I am
guessing the name boot is deceiving you as to its function.


> 2) The part which I dont get is why is "/" always ad2s1a - even when I create
> "/boot" first ? ("/boot" will become f.e. ad2s1d) and SWAP will become ad2s1b.
The first partition in a slice is considered the boot slice and '/' is
the boot partition.   
> So what I end up with is something like
> Size | Mountpoint | Device name | File system
> 15GB / /dev/ad2s1a UFS2
> 1024MB --- /dev/ad2s1b SWAP
> 100M /boot /dev/ad2s1d UFS2+S
> Any replies much appreciated.
> Best regards
> Nils Valentin
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