Archive
Posts from 2011
Viewing resource limits for Linux processes
Most Linux distributions ship with the pam_limits module to limit the resources that can be used by a process. You can enforce process resource limits by the user that a process runs as or by the group name a process runs as. These limits are set in /etc/security/limits.conf. To see the limits for your running shell you can run ulimit with the "-a" option: All of the limits above are the system defaults, since I haven't made any changes to /etc/security/limits.conf…
$ read more →Defragmenting EXT4 file systems with e4defrag (coming soon to a distribution near you)
If you have been around the systems engineering field you have probably read about file system fragmentation at some point. This typically occurs when files are randomly updated over time, and the blocks that comprise the file get scattered over different areas of the disk. This causes the drives to perform more work since the drive heads have to perform additional seeks vs. being able to sequentially read data off of a given platter…
$ read more →Concert review Guns N' Roses with special guest Buckcherry
If you've seen any of the concert reviews I've done in the past you would know that music is one of the things I love. I try to see as many shows as possible, and am constantly mixing up my musical genres. One day you will catch me listening to Alice In Chains, the next day I'll be listening to Toby Keith and the day after that I'll throw on some techno. Of all of the bands I've listened to, Guns N' Roses has probably received the most airplay on my home stereo (I have all of their albums, but Appetite For Destruction has definitely gotten the most airplay)…
$ read more →Using rpcdebug to debug Linux NFS client and server issues
Debugging NFS issues can sometimes be a chore, especially when you are dealing with busy NFS servers. Tools like nfswatch and nfsst at can help you understand what operations your server is servicing, but sometimes you need to get into the protocol guts to find out more info. There are a couple of ways you can do this. First you can capture NFS traffic with tcpdump and use the NFS protocol decoding features that are built into wireshark…
$ read more →Using wireshark's protocol decoding to debug NFS problems
Most admins have probobably encountered a situation where someone says "hey this really bizarre thing is occurring." Whenever I am approached to look at these types of issues I will typically start by jumping on my systems and reviewing system, network and performance data. Once I've verified those are within normal levels I will begin reviewing the client server communications to see what is going on. I've encountered some NFS issues that fit into the "bizarre" category, and it's amazing how much information you can glean by reviewing the NFS traffic between the client and server. I like to visualize problems, so I will frequently grab the network traffic with tcpdump: Re-create the issue and then feed the resulting dump into wireshark: Wireshark will decode all of the NFS procedures for you, which makes comparing the captured packet against the pertinent RFC super super easy…
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