[nycbug-talk] Re: MSNBC on the decline of technology jobs

alex at pilosoft.com alex
Wed Jun 22 21:51:08 EDT 2005

On Thu, 23 Jun 2005, Jed Davis wrote:

> > * How many fields in an IP header router will change while forwarding?
> > [ttl and crc]
> Record-route options, anyone?
200% credit for the question. :)

> > * Why should you have recursive dns server separate from authoritative
> > dns server [cache growth/cache poisoning]
> I was under the impression that modern nameservers resist cache
> poisoning, and if the cache can grow beyond reasonable bounds, You Have
Kind Of Sort Of.
> Other Problems.  As a general security principle, though, it nonetheless
> makes sense to isolate <thing that random people can feed malicious
> input to> from <source of important information>.  Especially if
> individual hosts don't have their own local slaves, so a dead or
> corrupted nameserver can devastate the entire network.
> > Unix admin questions:
> []
> > * What's an inode?
> The physical representation of a potential file.  The name "inode" kind
> of implies the traditional Unix filesystem or at least something similar
> to it it; for example, while HFS file id's are a little like inode
> numbers, and can be (and I think are) stuffed into st_ino, I don't know
> that it's terribly meaningful to talk about inodes with HFS.
Actually, concept of inode exists on any unix system, and is very separate
from the implementation of inode. (For example, you are guaranteed that if
two files have same ino as returned by fstat, they are same hardlinked
files). Points for pointing out that inode has permissions and not an 
individual directory entry. 

> > * What's a sticky permissions bit?
> Much like many aspects of Unix, it's something that makes more sense if
> you're a PDP-11.
Er not quite, see /tmp filesystem.
> > * When would you use tar vs cpio? [silly question - but at least it would 
> > show someone knows what cpio is]
> 1) cpio can be useful when you have a command like find(1) writing out a
> list of files (in a nontrivial directory tree) you need to archive or to
> copy somewhere.
> 2) Don't use either; use pax instead.  (-:
> > * You are trying to unmount filesystem, but it tells you 'busy'. How would 
> > you see what processes are using it? [fuser -m or lsof]
> This gets more fun when the open isn't from a user process, but because
> you swapctl -a'ed a file on the filesystem a while ago and forgot about
> it.  (In my defense, that was a test system, and also I was doing this
> at home.)
Great point. :)

> > * You screwed up boot block and server won't boot. You have the
> > original OS CD. How do you boot off the CD the OS on the current hard
> > drive? [very os-dependent, but in most cases boot -a will prompt you
> > for root fs]
> You don't, because you updated the system since the original install,
> and the new userland isn't compatible with the old kernel on the CD, and
> the bootloader isn't sufficiently powerful to nab the old kernel off the
> hard drive. (-:
Story of bad luck. That would also get full credit on the interview:)

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