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netstat Archives - AWS Managed Services by Anchor

The sysadmin’s essential diagnostic toolkit

By | Technical | 4 Comments

We’ve had a number of people ask us recently what sort of procedures and tricks we use when hunting down problems on systems we maintain, as a lot of the work can seem magical at times. While there’s no short answers to these sorts of questions (you could fill many, many pages with the topic), we thought we’d share some of the most commonly-used tools with you. You may already know a couple of them, which is great. Their real value comes from knowing how and when to use them. strace This is the big one for us, because it so frequently tells us exactly what we need to know. strace hooks into a process using the kernel’s ptrace facility and prints a list of all the syscalls made by…

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Firewalling VMware ESX for console access

By | Technical | No Comments

One of Anchor’s more recent product offerings is VMware-based virtual private servers. As one of my colleagues has already detailed, we take extra measures to secure the VMware host server to reduce the possibility of a compromise. Our VPS offering uses VMware ESX, which runs on bare metal and doesn’t have a host operating system. This isn’t the full story – according to documentation it boots a Redhat Enterprise Linux 3 system, then loads the vmkernel which is where the real work is done. One of the nice things about this approach is that there’s a userspace environment in which to run support software, like good monitoring components. We ran into an odd problem recently with an ESX host server on a dedicated network segment, namely that we couldn’t view…

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Firewall Hero III: Legends of Packet Filtering

By | Technical | No Comments

Customer support can be fantastically rewarding sometimes. When your combination of skill, tenacity and knowledge produce a solution that’s straightforward and effective, the feeling of satisfaction is hard to match. It doesn’t even have to be something big, we’ll take those small victories gladly. Our work sometimes looks a bit like magic, and we don’t mind one bit. A few weeks ago one of our customers reported problems with streaming media from their server. Clients were taking about 20-30sec to connect, which was of course unacceptable, and they were suspecting something was wrong on our side, perhaps congestion or some over-zealous border firewall. The redundant connectivity we purchase is well above requirements even in the face of failure, and we don’t oversell bandwidth, so the former wasn’t a possibility. We…

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