Archive
Posts from 2011
Using the Linux arping utility to send out gratuitious ARPs
I managed a number of Redhat and Heartbeat clusters. On a couple of occassions the services that manage the virtual IPs have misbehaved, and the storage has ended up on one node and the virtual IP on another. To fix this I need to manually move the virtual IP to the host it belongs on, and then issue a gratuitous ARP so other hosts on the network clear their ARP cache and use the MAC address associated with the device the virtual IP now resides on. The Linux arping utility can be used to send out a gratuitious ARP (an "ARP Request" or "ARP Response" is the actual item sent) to update hosts on your network …
$ read more →A simple and easy way to restart dropped SSH sessions on Linux servers
I frequently use OpenSSH port forwards to move around my various networks, and there is nothing worse than an SSH connection dropping when you make heavy use of them. Recently I came across the autossh utility, which provides a crazy easy way to monitor ssh sessions and restart them when they are reset or dropped. To use this awesome little tool, you can invoke autossh with the options you would normally pass to your ssh client: In the example above I am creating a dynamic local port forward that will accept connections on localhost:8000. To change how autossh manages the sessions and logs it creates, you can set one of more environment variables…
$ read more →New zone features in Solaris 10 update 9
I just finished reading through Frank Batschulat's slide deck of new zone features in Solaris 10 update 9. The new update on attach enhancements look extremely useful, and I have a few systems I will have to try to p2v using the tools that now ship with Solaris. If you are using zones, you should check out his presentation. Good stuff!
$ read more →Stopping your RHEL virtual interfaces from starting at boot. ONPARENT you say?
I recently debugged a pretty interesting problem with one of my clusters. When I rebooted one of the nodes, I noticed that a virtual interface that had ONBOOT set to no was started when the network interfaces were initialized. For those not familiar with RHEL systems, the ONBOOT directive tells the network initialization scripts not to start a given interface. This was rather confusing, and after some experimenting with a virtual machine I saw the EXACT same behavior…
$ read more →Who says Linux isn't stable?
I have been replacing some old hardware over the past few months, and recently noticed that we had several machines with uptimes in the hundreds of days (one 800+ days). For the longest time I thought only Solaris and AIX provided this kind of stability, but over the past few years I've started to include Linux in this list as well. You gotta love it when you see this: Now if only ksplice would make it into the Enterprise distributions! That would be rad, and I'm sure some fun "my uptime is better than your uptime" threads would ensue…
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