The following allows you to forward (NAT) traffic from an internal interface to an external interface (and back again ;]). In other words, creating a Gateway for a LAN (internal network).

Debian Based (apt-get)

1. # apt-get install iptables
2. # vi /etc/network/if-up.d/iptables

RedHat (rpm) Based

1. # yum install iptables
2. # vi /etc/sysconfig/iptables

1. #!/bin/sh
2.  
3. PATH=/usr/sbin:/sbin:/bin:/usr/bin
4.  
5. # user defined
6. WAN="eth0"
7. LAN="eth1"
8.  
9. # delete existing rules
10. iptables -F
11. iptables -t nat -F
12. iptables -t mangle -F
13. iptables -X
14.  
15. # always accept loopback traffic
16. iptables -A INPUT -i lo -j ACCEPT
17.  
18. # allow established connections, and those not coming from the outside
19. iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
20. iptables -A INPUT -m state --state NEW ! -i $LAN -j ACCEPT
21. iptables -A FORWARD -i $LAN -o $WAN -m state --state ESTABLISHED,RELATED -j ACCEPT
22.  
23. # allow outgoing connections from the LAN side
24. iptables -A FORWARD -i $WAN -o $LAN -j ACCEPT
25.  
26. # masquerade out LAN interface
27. iptables -t nat -A POSTROUTING -o $LAN -j MASQUERADE
28.  
29. # do not forward from wan to lan
30. iptables -A FORWARD -i $WAN -o $LAN -j REJECT
31.  
32. # enable forwarding packets from interface to interface
33. echo 1 > /proc/sys/net/ipv4/ip_forward

Debian Based (apt-get)

1. # chmod +x /etc/network/if-up.d/iptables
2. # sh /etc/network/if-up.d/iptables

RedHat (rpm) Based

1. # service iptables restart

Note that this config does not give the ability to provide DHCP or DNS services to LAN clients.

You can easily tar up a Linux box and extract the files on a Linux partition (some version of ext). This can be great for making an image of a dying hard-drive or putting a hard-drive in another box, mounting it, and then making a backup (great if you need to mount read-only).

The following creates an archive, gzips the archive for greater compression, verbosely prints to the screen what is being backed up, preserves all permissions, and stores it in a file "device" /path/to/archive.tar.gz.

History lesson: most implementations of tar still default to using a tape device as output for the file stream!

1. # tar -pczvf /path/to/archive.tar.gz \
2. > --directory=/ \
3. > --exclude=proc --exclude=sys --exclude=dev/pts \
4. > .

To decompress the archive to the current working directory:

1. # tar -pxzvf archive.tar.gz