Archive
Posts from 2006
Dumping HTTP requests and reponses to the Apache error log
When debugging problems with web applications, it is often useful to display the HTTP request and response headers along with the HTTP entity bodies. There are numerous ways to do this, and I covered several client centric solutions in my SysAdmin article Debugging Web Applications. Client side tools are extremely useful for pinpointing problems, but periodically it is helpful to see the raw requests from the client, and the responses from the server. If you happen to be running Apache, you can use the dumpio module to dump the request and response data to the Apache error log…
$ read more →Monitoring hardware sensors with the OpenBSD sensor daemon
In OpenBSD 3.9, the sensor framework was added to allow users to monitor systems that contained hardware sensors (e.g., temperature, voltage, fan speed, etc.). Sensor data is made available through one or more "hw.sensors" kernel state variables, which can be viewed with the sysctl utility: In addition to kernel support, OpenBSD has a userland daemon, sensorsd, which can be used to monitor one or more sensor values. If one of the sensor values that sensorsd is monitoring goes above or below an administrator defined threshold, sensorsd will by default write an entry similar to the following to the system log: Sensor thresholds are defined in the file /etc/sensorsd.conf. Each entry in /etc/sensorsd.conf contains the name of a sensor to monitor, the value "high" or "low" to indicate a peak or valley for the sensor value, and the value the sensor value cannot go above or below…
$ read more →Concert review Social Distortion
Social Distortion have been around for a long time, and they used to get a fair amount of airplay on the alternative radio stations I listened to back home. Mike Ness' vocals and guitar skills always amazed me, and I became a devoted Social D fan after listening to their "White Light, White Heat, White Trash" CD. I got a chance to see the band play live at a relatively small venue last night, and the show turned out to be chaotic and fun! The band took the stage around 10pm, with Mike Ness and company launching into an energized version of "reach for the sky" to start the show…
$ read more →Getting stack traces from Linux and Solaris processes
When an application is running, it is sometimes useful to see which stack frame the application is currently in. This is especially useful when debugging hung processes, since you can see which function the program is currently executing, and the code path taken to get to that point. Both Linux and Solaris provide utilities to capture live stack traces from processes. The Solaris tool to grab this information is called pstack…
$ read more →Speeding up Solaris zone creation with cloning
One really neat feature that was recently added to Solaris is the ability to clone zones. Cloning allows you to create a new zone from an existing zone, which can reduce provisioning time, and ensure that all zones are created consistently (e.g., all zones that will act as web servers can be cloned from a zone that was setup to act as a web server). If the zone you are cloning from resides on a UFS or VxFS file system, the clone operation will copy all of the files from the source zone to the new zone. If the zone that you are cloning from lives on a ZFS file system, the clone operation will create a writeable ZFS snapshot, and use that as the backing store for the new zone…
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