Archive
Posts from 2006
Greatest guitarists of all time
I got sick last Friday, and have been stuck at home all weekend recovering. While I was resting in bed yesterday, I set iTunes to play random music from my CD collection. iTunes was playing musical artists who I haven't listened to in several years (I can't recall the last time I actually listened to Magic Carpet Ride by Steppenwolf), and it got me thinking about who the best guitar players of all time were. There are TONS of awesome guitarists, and after pondering this I came up with my ten favorite guitarists: 1…
$ read more →Digging through the MBR (Master Boot Record)
I recently spent some time reading through the grub source code and the real mode assembly that resides in the MBR (master boot record). As I was reading though an explanation of the MBR real mode asembly code, I was amazed at how much cool stuff was packed into the 512-bytes that makes up the MBR (and of that 512-bytes, only 448-bytes are dedicated to storing machine code and error strings). The link above does a great job describing the real mode assembly, and in a nutshell the MBR code in that link does the following four things: The MBR first relocates itself (in the link above, the MBR is relocated to real mode address 0000:6C00). Once the MBR relocates itself, it loops through the partition table to find a partition that is marked active (i.e…
$ read more →Compressing Linux logfiles
I have a few Redhat Linux servers that log application data to one or more logfiles in /var/log. For some reason Redhat Linux doesn't compress the logfiles in /var/log by default, which can be a problem if your logging a lot of information, or if you need to keep logfiles around for historical reasons. To change this behavior and compress the logfiles that are stored in /var/log, you can uncomment the "compress" line in /etc/logadm.conf. This is a simple one line change, and the result should look similar to this: Once that change is made, the logfiles in /var/log will be compressed each time they are rotated.
$ read more →Limiting access to OpenSSH features with the Match keyword
With the introduction of OpenSSH 4.3p2, Darren Tucker introduced the "Match" keyword. This super nifty keyword can be used to limit features to specific users, hosts and groups, and allows administrators to enforce granular feature access (e.g., key-based authentication can only be used from specific hosts or subnets). To use the Match feature, the Match directive needs to added to the sshd_config configuration file with a criteria to enforce, and a set of directives to allow or deny. The Criteria can be either "User," "Group," "Address," or "Host," and wildcards are supported when the Host criteria is used…
$ read more →Viewing OpenBSD server utilization with systat
OpenBSD has a number of nifty utilities, and I happened to come across the systat(1) utility this weekend while looking for an executable in /usr/bin. Systat prints out performance data in an ncurses display, and can be used to view CPU saturation, I/O statistics, swap utilization, netstat data, and MBUF and network interface utilization. The utility takes the metric to display as an argument, and allows an interval to be used to control how often data is displayed: I absolutely love UNIX, BSD and Linux systems. There are so many nifty tools available for these operating systems, and it's a h00t when you come across a new utility that you didn't previously know about…
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