disk space for root vs users

[Richard Michael Todd]

jmm at skivs.UUCP (Joel M. Miller) writes:

>Has anyone noticed that available disk space is about 5,000K less
>when logged in as a normal user (eg Guest) than when logged in as root?
>Recall that I have set up my 80MB disk with "/" and "/users" on the
>same partition.  That is, when I log in as root, "df /dev/c5d0s0"
>says that I have about 7,000K available, while as jmm or Guest, 2,000K.
>I thought that the only difference between root and normal user logins
>was permissions.

  You obviously are new to machines with BSD-style filesystems.  On any
Unix machine with BSD-style FS (aka "Fast File System" or "UFS"), by default
10% of the disk space is reserved for root only.  The reason is that the
allocation policies BSD uses to allocate disk space "optimally" (i.e. not
fragmenting your file all over the disk, requiring mucho seeks), don't work
well when the filesystem gets more than 90% full.  Now, this policy works
fairly well on big university-owned machines (where BSD originated) where
they've got lots of big disks hanging off their Vaxen, but for those of us
with our dinky little 80M Quantums, we need that extra disk space.
Fortunately, the default can be changed with the "tunefs" command; check
out the man page on it.  You can set the "free space reserve" percentage
down to 0.  

>(A bit of self-defeating advice: don't even *think* of running A/UX off
>an 80 MB disk!  Self-defeating, because as soon as I scrape up money
>for a big disk, my 80 will be for sale!)

I agree, the 80M is a bit cramped, especially if you want to run netnews on
it.  (I did that under 1.1, with a very small set of newsgroups, but it
wasn't pretty, and I don't think I could have gotten away with it under
2.0).  Me, I added an external 300M instead of getting rid of my internal
80M.  I'd rephrase your advice to be "don't even think of running A/UX with
only 80M total disk on your system.  Especially if you like X Window :-).
-- 
Richard Todd   rmtodd at chinet.chi.il.us  or  rmtodd at uokmax.ecn.uoknor.edu  
"MSDOS is a Neanderthal operating system" - Henry Spencer