build/installworld break under -j n for n>1

Robert Watson rwatson at
Sun Jan 27 13:51:17 PST 2008

On Sun, 27 Jan 2008, Stefan Lambrev wrote:

>>> I'm guessing you would only do the make buildworld && make installworld if 
>>> you had *not* changed the kernel sources?
>> It is normally safe if you update frequently (<once a day)
> Changes in kernel are normally backward compatible, which means that in most 
> cases you should be able to run "old" world with new kernel. The opposite is 
> not true and you do not know when you will get bitten. In all cases you 
> should look at /usr/src/UPDATING, for special events :)

Let me put it slightly more strongly than you have: people will often not get 
bitten, but we guarantee that they will get bitten, and probably more 
frequently for taking the risk every day than for doing it once in a while. 
It is really not at all safe to update world before kernel, people who do so 
regularly and without following the commit logs *very* carefully will 
eventually get seriously hurt if they persist.

Keep in mind that UPDATING is generally only intended to help with bumpy 
patches in the regular and supported update process, and not to help people 
who do their own thing, so just checking UPDATING is not sufficient to make 
installworld before installkernel + reboot safe.

Robert N M Watson
Computer Laboratory
University of Cambridge

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