League of Professional System Administrators - Linux

Grub-booting memtest86 on x86 hardware

nomad — Tue, 08 Jul 2008 09:28:24 -0700

It is trivial to set things up so you are able to select memtest86 as a boot option in GRUB:

Download the latest memtest source from http://www.memtest86.com.

Extract and follow the instructions in the README that comes with it to compile. Copy the resulting memtest.bin to /boot and edit /etc/grub.conf to have the following 3 lines:

title Memtest86
        root (hd0,0)
        kernel /boot/memtest.bin

Make sure you reboot to test.

In theory this should work with any x86 OS + bootloader. I am doing this with RHEL 4 + GRUB.

How to remove IPv6 on Red Hat nodes

Aleksey Tsalolikhin — Sun, 03 Feb 2008 13:52:18 -0800

Picked up this tid-bit on how to disable IPv6 (which aligns with the general sys admin philosophy of "if we are not using it, remove it or turn it off to simplify the system and increase security":

(1) Edit /etc/sysconfig/network and set NETWORKING_IPV6=no.

(2) Issue the following command as root: 'chkconfig ip6tables off'.

(3) Reboot the host machine.

Notes on *nix atime

ski — Thu, 09 Aug 2007 12:53:38 -0700

Read an interesting discussion on the lkml list where Linus and friends talked about atime's performance impacts (http://kerneltrap.org/node/14148). Ingo phrased the problem best with:

' For every file that is read from the disk, lets do a ... write to
the disk! And, for every file that is already cached and which we
read from the cache ... do a write to the disk! '

Solutions are to mount your file systems with the noatime, nodiratime options. The only time this may cause a problem is if you have a local mail spool (the mailer will not know that new email arrived) or possibly with some backup software.

Asking for Comments: Samba Server Setup Experience Under Fedora Core 6

ant — Wed, 23 May 2007 12:43:29 -0700

Solved -- The box didn't retain my permissiable SELinux environment after a yum update. With a 'sudo setsebool -P samba_enable_home_dirs=1' there was a mighty noise and it started allowing public read-only access to the share.

Someone liked my work (that they help me do) so well, that recently they requested I share the file with everyone on the LAN. I set out to create a publicly readable Samba share for the file. As a user, I issued a 'sudo yum install samba' and soon after started working on the default config file in /etc/samba/smb.conf.

Here's the mix I came up with (which, keep in mind, doesn't work; I could use some help!)

Django

eadmund — Mon, 22 Jan 2007 13:08:07 -0800

Short Description:
Excellent Python web development framework

Home Page:
www.djangoproject.com

Release Date:
Fri, 2005-07-15 14:00

Status:
Stable

Long Description:

I like to use this to throw together nice web frontends for the PHBs to look at stats & stuff. It's pretty simple to use, interfaces easily to a database--very useful for the sorts of sysadmin-plus stuff I tend to do.

NMAP

dklein — Sun, 14 Jan 2007 09:50:04 -0800

Short Description:
Fast enumeration of network services

Home Page:
insecure.org/nmap

Release Date:
Sun, 2007-01-14 10:00

Status:
Active

Long Description:

Nmap is a powerful tool for discovering hosts on a network and enumerating what service they are offering. This can be used to find vulnerable systems, to locate rogue services on your network or simply for a first step in troubleshooting.

Fun with FC6 and acpi-cpufreq.

hcoyote — Wed, 01 Nov 2006 20:12:54 -0800

I finally discovered why I couldn't do cpu scaling on my Inspiron 6000. Apparently the default kernel for FC6 is an i586 kernel. It also doesn't work with acpi-cpufreq. It's broke. It no-workie. How do you make it work? Why, you install the i686 version of the kernel!

Simple you say? Oh sure, you just download the rpm, -ivh it, and run! Right? Nope. It sees it as the same kernel rev so complains. Ok, so let's whip out the --force. Great, it chugs along, and chugs along, and ... chugs ... and ... continues ... and ... no disk light ... and ... and ... and ... and? Hmm.

Apparently lvm.static doesn't like something about the stock LVM setup that anaconda gives you. It kept locking up in i/o wait trying to figure out what hte config was so it could do something with mkinitrd (atleast, I presume; it was in the post install for the kernel).