OpenSSH is a flexible tool for not only logging into other servers, but to also help tunnel other network traffic. The following article is a grab-bag of useful SSH tips.
Using the per-user configuration file, ~/.ssh/config you can make your life a bit easier. One common scenario is that a SSH server you commonly use is listening on a non-standard port. To save you from the strain of typing out -p ... [continue reading]
Ever wanted to record a log of an interactive console session? Easy, just use the script utility. It’s probably already present on your system, no installation required.
To start recording, run script --timing=script.tim script.log. This spawns a new shell, recording stops when you exit from it.
To replay the log, run scriptreplay script.tim script.log. It is also possible to speed up or slow down the playback speed. For example, in order to play back ... [continue reading]
I’m sure we all have had “that feeling once”. You patch your desktop or laptop, then type in reboot in a shell in order to boot your computer. And that crucial server you were working on starts shutting down.
But fear not - a solution exists for this and similar problems.
Molly-guard was (according to Internet) originally a improvised plexiglass cover shielding the kill switch on an IBM 4341. It was named after a programmers daughter - Molly ... [continue reading]
When building a Ceph-cluster, it was important for us to plan ahead. Not only does one usually start out with a minimum of ~5 servers, but one should also expect some growth in the cluster. Running the cluster also means patching the operating system and Ceph itself, and with Ceph being a crucial infrastructure component it’s also desirable to have a proper rollback procedure.
We’ve grown really fond of ram-disk nodes. Using a Jenkins ... [continue reading]
The poor referer header. Misspelled and misused since its inception.
Its typical use is thus: if I click on a link on a website, the referer header tells the landing page which source page I came from.
Source URL = www.mysite.com/page1 -> Target URL = www.example.com referer = "www.mysite.com/page1" It’s heavily used in marketing to analyse where visitors to a website came from, and also very useful for gathering data and statistics about reading habits ... [continue reading]
How often do you do this:
service_foo.conf,service_foo.conf,foo,service_foo.conf,It’s pretty common.
Or:
$ long_running_command # Darn, should've started it in the background instead! CTRL-C $ long_running_command & All of these situations can be dealt ... [continue reading]
In a recent sysadvent article I described how to configure BIND with a Response Policy Zone. Using an RPZ can efficiently thwart outbound network traffic based on one’s own preferences, and it can be extended to import and/or subscribe to externally provided DNS zones.
My local BIND server has been configured with two RPZs. One is maintained manually, mostly for reaching internal resources behind a NAT firewall by their official DNS names. The other one ... [continue reading]
Apache JMeter is a nice little tool with tons of functionality for testing web sites. It can be used both for stress testing and functional testing. This tutorial is going to show you how to set it up and get started with some basic stress testing.
First, go to the official Apache JMeter website and download the binary, and unpack it on the machine you will be running the test from (your workstation/laptop should ... [continue reading]
It is late night. You have just arrived at your Grandparents, when the SMS beeper goes off. There is a problem with a SAN controller, and the on-call person know you fixed it the last time. Now, if you only had documented it.
You know you have to fix this yourself, but you have no VPN access. You don’t even have an Internet connection, except your 3G mobile phone, and you really need access to that admin web GUI. There ... [continue reading]
In bash, we often use redirects (that is < and > ) to get output from a command to a file, or input from a file to a command. But sometimes, commands takes two or more files as input. Then our ordinary scheme does not work anymore.
Let’s say you want to diff(1) the output of two commands. For example, compare the contents of two directories. ... [continue reading]