One or Four?

Devin Teske devin.teske at fisglobal.com
Sat Feb 18 01:05:23 UTC 2012



> -----Original Message-----
> From: owner-freebsd-questions at freebsd.org [mailto:owner-freebsd-
> questions at freebsd.org] On Behalf Of Da Rock
> Sent: Friday, February 17, 2012 4:55 PM
> To: freebsd-questions at freebsd.org
> Subject: Re: One or Four?
> 
> On 02/18/12 10:40, Chuck Swiger wrote:
> > On Feb 17, 2012, at 4:11 PM, Devin Teske wrote:
> >>> However, for whatever reasons, the overwhelming majority of folks using
> MacOS
> >>> X don't have problems using a single root partition, and while they
> sometimes do
> >>> fill up their disks, that's a situation which they should be able to
recover from
> >>> without needing expert assistance.  I don't recall having unusual issues
in
> running
> >>> a partition out of space under FreeBSD, either, or difficulty fixing
things
> >>> afterwards--
> >> Recipe for disaster:
> >>
> >> 1. You have a cron-job that pulls down /etc/master.passwd daily
> >> 2. Your cron-job also runs pwd_mkdb after "SUP"ing down
> /etc/master.passwd
> > Yes, I agree that this is a recipe for disaster; the reasons not very
correlated to
> disk space, however.
> >
> > Even twenty years ago, handling this via YP/NIS or NetInfo would have made
> more sense, and nowadays folks would be far more likely to use LDAP as the
> network user database, instead of pushing system password database changes
> via SUP or similar replication mechanism locally to individual hosts.
> >
> >> 3. A program fills "/"
> >> 4. cron fires
> >> 5. pwd_mkdb can't generate databases because not enough room on
> filesystem
> >> 6. System can no longer be logged into
> > #5 does not imply #6: if pwd_mkdb can't build a temporary version to
> /etc/pwd.db.tmp&  /etc/spwd.db.tmp, it will exit with an error rather than
> invoke rename(2) to replace the working version of the password database with
> something that might be broken.
> 
> >
> > To be very specific, I would expect one to get:
> >
> > "/: write failed, filesystem is full
> > pwd_mkdb: /etc/pwd.db to /etc/pwd.db.tmp: No space left on device"
> >
> >> 7. System is rebooted
> >> 8. Can't log in (not even as root)
> >> 9. Go into single-user mode
> >> 10. No space to work in
> >>
> >> Sure... you can call it an "edge-case," but it's pretty common and this is
only
> >> one of a myriad of ways we can reproduce the problem of filling-up "/" to
> cause
> >> major headaches.
> >
> > I've never heard of such a thing happening to a real FreeBSD system in the
past
> decade or more.  The closest match to the issue results in a failure of
adduser(8)
> or pw(8) to add new users, but existing users continued to work fine.
> These are edge cases that _do_ happen - Linux (heaven forbid!) is
> reknown for the all /, and I've been unable to boot properly into it
> with a full disk. I had to use a live disk to rescue it which took hours
> thanks to the $%^&! lvm filesystem.
> 
> Its just so easy to run a multi partition as opposed to an all /. And
> how much does it cost/hurt to do it (especially given the inordinately
> large hdd's these days)? Next to nix (pardon the pun :) ). The reduction
> in problems for new users should be an incentive as well.
> 

+1

I imagine an increased load on -questions@ for users that need extra
hand-holding when they fill their entire disks versus incidentally filling a
single partition. One requires instructions involving a live disc versus the
latter which involves dinking with a still-very-usable system. Time-to-recover
is inordinately skewed between the two situations, IMHO
-- 
Devin

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