Archive
Posts from 2009
Decoding PCI data and lspci output on Linux hosts
I've been spending some time reading the source code to the Linux QLogic HBA source code, and got a bit curious about how PCI device data was represented by the kernel. I took a number of notes while reading through the Linux kernel documentation, and summarized them in an article titled Decoding PCI data and lspci output on Linux hosts. If you are interested in learning more about how to decode PCI device-nodes, check out the article.
$ read more →Gaining access to Dell drivers and openmanage software though yum
Dell has supported Linux on their PowerEdge server line for several years. I just came across the Dell Linux wiki, and more importantly the Dell OMSA Repository. This repository is a one stop shop for Dell-specific drivers and the OpenManage monitoring and reporting software. I'm hoping to fire up my Dell 2850 later this week so I can play around with OpenManage and the network repository…
$ read more →Managing loop devices on CentOS and Fedora Linux hosts
Linux loop devices provide a way to mount ordinary files as block devices. This capability allows you to easily access an ISO image that resides on disk, mount and unmount encrypted devices (the dm-crypt and fuse encryption module may be a better solution for this), or test out new file systems using plain old files. Linux loop devices are managed through the losetup utility, which has options to add, list, remove and locate unused loop devices. To associate a loop device with a file, you will first need to locate an unused loop device in /dev…
$ read more →Increasing the number of available file descriptors on Centos and Fedora Linux Servers
While debugging an application a few weeks back, I noticed the following error in the application log: Cannot open file : Too many open files The application runs as an unprivileged user, and upon closer inspection I noticed that the maximum number of file descriptors available to the process was 1024: Increasing the maximum number of file descriptors is a two part process. First, you need to make sure the kernel's file-max tunable is set sufficiently. This value controls the number of files that can be open system-side, and is controlled through the file-max proc setting: Once you know you have enough file descriptors available, you will need to add an entry for the user to the security limits file (/etc/security/limits.conf). This file is used to control resource limits for users and groups, and is processes when a user login session is initialized…
$ read more →Managing /etc/sysctl.conf with the sysctl utility
The Linux kernel provides the sysctl interface to modify values that reside under the /proc/sys directory. Sysctl values are typically stored in /etc/sysctl.conf, and are applied using the sysctl utility. To set a sysctl variable to a specific value, you can run sysctl with the "-w" (change a specific sysctl variable) option: To apply all of the settings in /etc/sysctl.conf to a system, you can run sysctl with the "-p" (apply the sysctl values in /etc/sysctl.conf to a running server) option: The sysctl interface is pretty powerful, and can you learn more about the individual sysctl variables by perusing the Documentation/sysctl/ directory that ships with the Linux kernel source code.
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