List used fwmarks

iptables -t mangle -L PREROUTING -n | awk -F "MARK set " '{print $2}' | sort -u

List all virtual servers with fwmarks in a given subnet

for x in `iptables-save | grep 10.8.28 | awk '{print $NF}' | awk -F / '{print $1}'`; do ipvsadm -lnf $(($x)) | cat -n; done

Change the weight for a real server

ipvsadm -ef 123 -r 10.0.0.23:0 -w 0

Using LVM for "/" partition

Unlike when using normal partitions, you can't use root=/dev/mapper/lvm-location in lilo.conf to specify the root partition. The reason is that lilo converts that location to /dev/dm-0, or /dev/dm-1, or whatever it happens to be mapped to at the time. The problem with that is /dev/dm-* are dynamically allocated at boot, and are likely to be different every time.

Port-based Redirect

assuming 10.2.3.4 is the ip of the box we are redirecting to and 10.2.3.5 is the ip of the box handling the redirect. Forwarding port 3306

echo "1" > /proc/sys/net/ipv4/ip_forward
iptables -P FORWARD ACCEPT
iptables -A FORWARD -i eth0 -p tcp --dport 3306 -j ACCEPT
iptables -t nat -A PREROUTING -p tcp -i eth0 --dport 3306 -j DNAT --to-destination 10.2.3.4:3306
iptables -t nat -A POSTROUTING -o eth0 -j SNAT --to-source 10.2.3.5

To undo this

Redirect with paramaters and values using $V$P

Global Settings

Allow cluster to retry failed actions instead of just giving up

crm_attribute --attr-name start-failure-is-fatal --attr-value FALSE

Require explicit permission for a given node to run a given service

crm_attribute --attr-name symmetric-cluster --attr-value false

Force resources to stay where they are if their original location comes back online

Install Grub on Drive

Install grub to first hard drive (hd0)

# grub --no-floppy
grub> root (hd0,0)    (Specify where your /boot partition resides)
grub> setup (hd0)     (Install GRUB in the MBR)
grub> quit            (Exit the GRUB shell)

Automatically install grub to first hard drive

# grub-install --no-floppy /dev/sda

Merge Two or More PDFs into a New Document

pdftk 1.pdf 2.pdf 3.pdf cat output 123.pdf

CHROOT from Live CD

mount /dev/ /mnt
mount -t proc none /mnt/proc
mount -o bind /dev /mnt/dev
chroot /mnt /bin/bash
mount -a

Share an X11 Session via VNC

x11vnc -display :0

Show Firewire Devices

plugreport

Sort groups by GID

cat /etc/group | sort -t : -k 3 -n

Get next local UID

Installation

Instructions for using Dell's yum repository are available at http://linux.dell.com/repo/hardware/

wget -q -O - http://linux.dell.com/repo/hardware/OMSA_6.1/bootstrap.cgi | bash
yum install srvadmin-all
srvadmin-services.sh start

Create a new RAID device

omconfig storage controller action=createvdisk controller=0 raid=r1 size=max adisk=0:0:0,0:0:1

VMware has a very good tool called VMware Converter to convert a physical Windows machine into a virtual machine. However, what happens when you want to do the same for a Linux machine? VMware Converter does not support this. Fortunately, there is a way using a live Knoppix CD and netcat.

Disable IPv6

echo "blacklist ipv6" >> /etc/modprobe.d/blacklist.conf
reboot

Enable UTF-8

On debian based systems, you can enable UTF-8 support by running

dpkg-reconfigure locales

Make sure to select the UTF-8 character set that you want to enable.

Recompile deb Package

Make sure a "source" source is defined in /etc/apt/sources.list. Something like this

deb-src http://http.us.debian.org/debian lenny main contrib non-free

Then, the basic steps are