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Posts in Linux
Using the Linux netconsole service to send console messages to remote hosts
Most Linux distributions ship with the netconsole service, which allows kernel printk() messages to be sent to a remote destination. This feature can be useful for debugging system hangs and panics, and is handy for archiving console messages to a central location. To configure netconsole, you will need to add the IP address of a remote syslog server to /etc/sysconfig/netconsole. Here is a sample entry: Once the IP is added to the configuration file, you can start the netconsole service: This will load the netconsole kernel module, and write the configuration that was used to the system logs: If the netconsole service starts up successfully, each console message should be routed to the remote syslog server…
$ read more →Adding storage, network and 3rd party kernel modules to a Linux initrd image
While playing around with initrd images a few weeks back, I came across the mkinitrd "--with" option. This option allows you to add additional modules to an initrd image, which is useful when you have a new storage or Ethernet driver that isn't supported by the base operating system. To use this option, you can place the names of the modules to add to the initrd image in quotes, and pass them to the "--with" option: To verify the image contains the modules you specified, you can extract the initrd image and poke around the lib/modules directory: If you want the modules included in all future mkinitrd runs, you can add the modules to the modules variable in the/etc/sysconfig/initrd file. Nice!
$ 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…
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