Archive
Posts from 2009
Getting tape drive throughput and performance statistics on Linux hosts
I manager a number of Linux Netbackup media servers, and just recently learned that Linux doesn't provide a tool to view tape statistics (it appears there are no /proc interfaces to retrieve SCSI tape drive performance data). Fortunately the SystemTap developers saw this glaring deficiency, and created the iostat-scsi.stp script to display statistics for each SCSI tape and disk device in a server. To use SystemTap on a Redhat, CentOS or Fedora Linux host, you will first need to install the kernel debuginfo files. Here are the commands I used to install the debuginfo RPMs on a Redhat Enterprise Linux machine (you can download the RHEL debuginfo files from the Redhat FTP server, and you can get the debuginfo files for CentOS and Fedora from one of the various mirrors): Once the debuginfo files are installed, you can download the iostat-scsi.stp script from the systemtap website…
$ read more →Switching between the KDE and GNOME window managers on Centos and Fedora Linux hosts
I recently switched a Fedora host from the GNOME window manager to KDE. This exercise allowed me to familiarize myself with how X and the various window managers are organized on Fedora hosts, and I thought I would jot down how to switch between window managers for future reference. When a Fedora host is booted into run-level 5, the following initab entry will cause the X server and Window manager to start: The prefdm script uses the /etc/sysconfig/desktop file to control which window manager (KDE or GNOME) is started, as you can see in the following code snippet from the script: So to set the default window manager to GNOME, you can set the DISPLAYMANAGER variable to GNOME: To use KDE, you can set the DISPLAYMANAGER variable to KDE: I dig the fact that Fedora and CentOS Linux servers control application settings through configuration files in /etc/sysconfig. This makes it easy to adjust application settings, and ensures that a package update won't whack your customizations…
$ read more →Using the ssh config file to set specify remote usernames
I periodically need to access remote systems using different userids (I didn't have control over the account creation process, and unfortunately LDAP isn't in use :( ). While I could use the username@host syntax to specify a userid, I find it easier to list the userids in the .ssh/config configuration file. Here is a sample configuration I use on one of my systems: The User directive can be applied to each Host configuration stanza, which allows you to specify a unique userid for each host (or group of hosts) you connect to. There are a number of cool SSH options, which are documented in the ssh_config(5) manual page…
$ read more →Restarting X and the GNOME window manager on Linux hosts
I useGNOME as my primary desktop at work, and periodically need to restart the Xserver / windowing environment to pick up new changes. If I have an X environment up and running, I will send a cntrl + alt + backspace to restart the X server. If for some reason I'm not able to send the key sequence above (this isn't feasible if I'm logged in remotely), I will run the telinit command to switch to run level 3 (multi user mode w/o X), then execute it a second time to switch back to run level 5 (multi user mode w/ X): The latest GNOME bits are pretty slick, though I'm starting to dig KDE again (I used to use KDE years ago). I plan to share my experience with the latest KDE bits in a future post.
$ read more →Monitoring traffic across a Solaris 802.3ad link aggregation
I manage a number of Solaris hosts that push a fair amount of data each day. These servers utilize Solaris 802.3ad link aggregations, which contain anywhere from 4 to 8 physical NICs. Monitoring the bandwidth across the links in an aggregation is a snap with Solaris, since most of the dladm subcommands support the "-s" (show statistics) option: In the example above, dladm printed the number of bytes and packets received for each link in the aggregation that was created with key number 1. While not quite as awesome as nicstat, the statistics option is handy for getting a quick overview of the number of packets and bytes traversing each link.
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