Eight day in Addis

Fri, 05 Jun 2009 22:57:39 -0000
eng, etiopia, pdo, tips

Useful things to keep in mind when setting up a service:

always take note of what you do

make yourself always able to explain to another person what you did

keep a copy of the configuration files before changing them, so that you can see what you changed

be always able to move the service to another computer

make sure that it works after reboot

Example use of vim block selection:

ESC: exits insert mode.

^V: starts block selection. Move the arrows to form a rectangle.

c: change. Type the new content for the line.

ESC: gets out of insert mode, and the change will happen in all the lines.

To change network configuration with config files, edit:

/etc/network/interfaces

To also setup DNS in /etc/network/interfaces, use dns-search and dns-nameservers (for this to work, you need to have the package resolvconf):

dns-search dream.edu.et
dns-nameservers 192.168.0.1 192.168.0.2

To make a router that connects to the internet on demand using a modem:

apt-get install diald

To see the path of network packets:

mtr 4.2.2.2

Basic NAT script:

OUT=eth2
IN=eth0

modprobe iptable_nat
iptables -t nat -A POSTROUTING -o $OUT -j MASQUERADE
echo 1 > /proc/sys/net/ipv4/ip_forward

What happens at system startup:

1. the BIOS loads and runs the boot loader

2. the boot loader loads the kernel and the inintrd ramdisk and runs the kernel

3. the kernel runs the script 'init' in the initrd ramdisk

4. the script 'init' mounts the root directory

5. the script 'init' runs the command /sbin/init in the new root directory

6. 'init' starts the system with the configuration in /etc/inittab

To install a new startup script:

sudo ln -s /usr/local/sbin/firewall /etc/init.d
sudo update-rc.d firewall defaults 16 75

Normally you can just do:

sudo update-rc.d [servicename] defaults

To have a look at the start and stop order numbers, look at /etc/rc2.d for other start scripts and /etc/rc0.d for other stop scripts

To test a proxy, low level way:

$ telnet proxy 8080
Trying 192.168.0.6...
Connected to proxy.dream.edu.et.
Escape character is '^]'.
GET http://www.google.com HTTP/1.0 [press enter twice]