Category Archives: Sundry sysadmin

Find out what is using your swap

Have you ever logged in to a server, ran `free`, seen that a bit of swap is used and wondered what’s in there? It’s usually not very indicative of anything, or even overly helpful knowing what’s in there, mostly it’s a curiosity thing.
Either way, starting from kernel 2.6.16, we can find out using smaps found in the proc filesystem. I’ve written a simple bash script which prints out all running processes and their swap usage. Continue reading

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Site slow after scaling out? Yeah, possibly!

So, doing the maths, you’re seeing 25*0.2*50= 250ms in just network latency per page load for your SQL queries. This is obviously a lot more than you see over a local UNIX socket. Continue reading

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GlusterFS init script and Puppet

I got most of it set up, and got started on writing up the glusterfs Puppet module. Fairly straight forward, a few directories, configuration files and a mount point. Then I came to the Service declaration, and of course we want this to be running at all times, so I went on and wrote… Continue reading

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Legitimate emails being dropped by Spamassassin in RHEL5

Over the past few months, an increasing number of customers have complained that their otherwise OK spam filters have started dropping an inordinate amount of legitimate emails. Continue reading

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Control groups in RHEL6

One new feature that I’m very enthusiastic about in RHEL6 is Control Groups (cgroup for short). It allows you to create groups and allocate resources to these. You can then bunch your applications into groups at your heart’s content. Continue reading

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