Maintaining Repos in Kickstarted Machines After Install

After you've installed a machine, its install-time repository config in /etc/yum.repos.d is pretty much set.

Bah, I say! Bah! Just keep it updated.

Kickstart (cobbler):

#set yumconfcronfilename = "/etc/cron.daily/50-yum-config-stanza"
cat << EOECYCS > $yumconfcronfilename
#!/bin/sh
$yum_config_stanza

sed -ne '
        /^baseurl=/{
                s/baseurl=/repomd /
                s://:__:
                s:/: :
                s:__://:
                p
        }
        ' /etc/yum.repos.d/cobbler-config.repo \
          > /etc/apt/sources.list.d/cobbler-config.list
EOECYCS
chmod a+x $yumconfcronfilename

If you're not running cobbler, set it into place by hand:

cat << EOECYCS > /etc/cron.daily/50-yum-config-stanza
#!/bin/sh
wget "http://archive/cblr/svc/op/yum/profile/centos5-i386-minimal" --output-document=/etc/yum.repos.d/cobbler-config.repo

sed -ne '
 /^baseurl=/{
  s/baseurl=/repomd /
  s://:__:
  s:/: :
  s:__://:
  p
 }
 ' /etc/yum.repos.d/cobbler-config.repo \
   > /etc/apt/sources.list.d/cobbler-config.list
EOECYCS

chmod a+x /etc/cron.daily/50-yum-config-stanza

That's dereferenced for you. The actual profile's going to be way off, though, so don't use that one verbatim. Find your own:

awk -F/ '/^url/{print $NF}' anaconda-ks.cfg

As usual, watch carefully for the way in which the 'new', 'better' blogspot editor makes an artistic puree of the quoted stuff;  grain of salt, kids.

Pruning Bogus Value Spikes from MRTG Gauge Values after a Reboot

MRTG is awesome and simple.  I use it in a bunch of places to quickly figure out roughly what's going on over my networks and servers.  Traffic numbers, disk space, the usual stuff.  My usage of it is strictly ghetto, but it works really well for me even when I misuse it.

When I reboot a machine, though, I find my gauges all spike.  Traffic numbers, CPU load, etc, there's a spike right at the point where I rebooted the machine.  It seems to be that MRTG sees the gauge is reset, but it treats it as an overflow, as if the gauge wrapped around, and not as if it's been zeroed out.  So the spike may be its attempt to account for the massive jump in data that would cause a wraparound.

the only solution I have just yet - because I can't use ABSMax or MaxBytes parameters - is to prune the ugly data points:

val=500000; \
for F in /var/www/html/mrtg/{cpu,dev-*}/*.{log,old};\
  do awk -vX=$val '
    NF < 4 || ($2 < X && $3 < X && $4 < X && $5 < X)
  ' $F | diff -u $F - | patch $F;\
done

Really, though, you should use the ABSMax and MaxBytes parameters whenever and wherever you can.  It'll prevent this spike when you reset your machine.

Finally, I'm sorry if the above code snippet looks like absolute ass.  There is some formatting for reading ease, while I usually do it all on one line, but also what is with the pathetic format munging in this 'new, better' editor?  It's horrid!  Can we roll it back, please?

TCPDump Top-Talkers script

I remember back in the days of cypress Linux, or Red October, that we in the MH office had a top talkers script.  It was good to see, for instance, that the streaming radio you were listening to didn't impact the network too noticeably.  I don't know what the network guys did out there, but I had a need to cook up something out East again.  So I googled it up, found a tcpdump cheat-sheet with it, and there ya go.  Top talkers:

tcpdump -tnn -c 20000 -i eth0  |\
   awk -F "." '{print $1"."$2"."$3"."$4}' |\
   sort | uniq -c | sort -nr |\
   awk ' $1 > 100 ' 

It's nothing like perfect, for it only shows the number of packets a machine's blowing out the NIC and not the size of each one, but that's something which we can add in, I figure.  It's quick, though, and gives a relatively useful ballpark figure, which is all I need today.

Yay for google and tcpdump!

Find your RAID MD Device Name from a Member Device

So you've got a bajillion RAID arrays; that's okay, really.  Thing is, if you need to find its mdX device, it can get tricky.  vGrep taxing the eyes?  Mine too, and I haven't had much luck with an alternative.  I know there's one out there, but I have yet to trip over it.

Here's what I've started doing:

mdadm --detail --scan |\
awk '/'`mdadm -E /dev/sde3|awk '/UUID/{print $NF}'`'/{print $2}'

/dev/md6

 Substitute in your own values for /dev/sde3.