Posts tagged: linux

Redirecting a port to another host on same LAN using iptables

By , 2010-11-27 22:53

I have a strange situation where I want to redirect a specific port on one host to another host. That is, traffic to 192.168.1.100:8080 => 192.168.1.101:8080.

Found the answer on LQ forums.

iptables -A PREROUTING -t nat -p tcp -d 192.168.1.100 --dport 8080 -j DNAT --to-destination 192.168.1.101
iptables -A POSTROUTING -t nat -p tcp -d 192.168.1.101 --dport 8080 -j SNAT --to-source 192.168.1.100

Don’t ask me why this works. It just does. Well, the first line makes sense, but I have no idea what the second is doing.

After looking at the rule in Webmin, I think I figured it out.

  1. When a packet arrives at this computer, if protocol is TCP and destination is 192.168.1.100/32 (local IP) and destination port is 8080 then Destination NAT (change destination IP) to 192.168.1.101
  2. When a packet leaves this computer, if protocol is TCP and destination is 192.168.1.101/32 and destination port is 8080 (as would be the case for any packet modified by the above rule), then Source NAT (change source IP) to 192.168.1.100. (This ensures that the remote host .101 returns any packets via this computer, .100, rather than simply attempting to send them to the original requesting host.)

Update: This even works on an OpenVZ container! Just need to enable iptables nat in the vz config on the hardware node (VM host) [source].

nano /etc/vz/vz.conf

Then do Control W and SEARCH for IPTABLES

Comment out (by adding a # symbol to the line ) the current IPTABLES= line

and then copy/paste and add this line directly underneath the line you just commented out.

IPTABLES="ipt_REJECT ipt_recent ipt_owner ipt_REDIRECT ipt_tos ipt_TOS ipt_LOG ip_conntrack ipt_limit ipt_multiport iptable_filter iptable_mangle ipt_TCPMSS ipt_tcpmss ipt_ttl ipt_length ipt_state iptable_nat ip_nat_ftp"

It is important to make sure this is all in 1 line and that it does not wrap.

Now Control-S and save – overwriting the current file.

Finally do an /etc/init.d/vz restart
to restart openVZ.

Triple-Booting Macbook Pro

By , 2009-10-05 13:01

It’s been a week now and I still have had no success installing all 3 major OSes on my MBP. OSX+Windows works fine (via Bootcamp), OSX+Ubuntu 9.10 also (9.04 hangs on boot).

This, however looks promising:
http://tubeshards.wordpress.com/2006/12/05/install-windows-to-a-macintosh-usb-drive/

Simple FLAC to MP3 shell script

By , 2009-09-10 21:41

For unix-like systems (Mac OS X, Linux). A simple shell script to convert flac to lame mp3.

Install flac, lame and id3tool

#!/bin/bash
for a in *.flac
do
OUTLAME=`echo "$a" | sed s/\.flac$/.mp3/g`
ARTIST=`metaflac "$a" --show-tag=ARTIST | sed s/.*=//g`
ALBUM=`metaflac "$a" --show-tag=ALBUM | sed s/.*=//g`
TITLE=`metaflac "$a" --show-tag=TITLE | sed s/.*=//g`
GENRE=`metaflac "$a" --show-tag=GENRE | sed s/.*=//g`
TRACKNUMBER=`metaflac "$a" --show-tag=TRACKNUMBER | sed s/.*=//g`
YEAR=`metaflac "$a" --show-tag=DATE | sed s/.*=//g`
flac -c -d "$a" | lame -m j -q 0 --vbr-new -V 0 -s 44.1 - "$OUTLAME"
id3tool --set-title="$TITLE" --set-track="${TRACKNUMBER:-0}" --set-artist="$ARTIST" --set-album="$ALBUM" --set-year="$YEAR" --set-genre="${GENRE:-12}" "$OUTLAME"
done

Edit: Apparently this has been done before…
http://pastebin.com/f641a9b21

MythTV/Proxmox (OpenVZ) multi-role server from hell

By , 2009-09-01 22:35

So… I just spent two hours trying to get MythTV running properly on my OpenVZ server (installed via the Proxmox VE bare-metal installer). This is starting to be a lot harder than I thought it would be…

As seen in my previous post, I installed the 2.6.26-2-openvz-amd64 kernel and headers, and compiled v4l-dvb from mercurial, and fixed a little bug with vzctl. Today, I installed the firmware files for my Hauppage HVR-1600 (see MythTV wiki page), added the Debian-multimedia repo and installed MythTV (apt-get install mythtv). Then I realized I needed X to use mythtv-setup, so for some reason I decided to install KDE 3.5. KDE installed fine (minus some missing files for the kdm theme… wonder why these aren’t included in the kdm package or a dependency…). I then proceeded to create a password for the mythtv user ($passwd mythtv as root) and then run mythtv-setup as the mythtv user. I managed to add the sources and scan for channels, but when I tried to “Watch TV”, I was told that the primary backend wasn’t running.

I tried some troubleshooting, but it’s getting kinda late and I’m lacking sleep (as you can probably tell from my grammar), so I decided to try installing a shiny new Intel Pro 1000 Desktop (82574L) PCIe x1 Ethernet card to get my server some gigabit love. Should be simple, right? Intel cards have good driver support, with the e100 and e1000 drivers, so much so that VM solutions like VMware and VirtualBox chose to emulate them as guest hardware. Well, this was not the case today. I popped the card in to a free PCIe x1 slot and powered on the PC. Link lights went on and all looked fine and dandy. But once the machine fully booted up (takes a while with all those OpenVZ containers 😉 ), ifconfig showed only the eth0 interface, which is my built-in Realtek/nForce controller. Some further probing with lspci and dmesg showed that the card is alive, but that the e1000 driver didn’t even bother to start up.

At this point, I GIVE UP for tonight. I’m cold from sitting down in the basement, tired from lack of sleep, and frustrated from uncooperative Linux servers.

No streaming TV for me tonight, but I suppose I should be glad that at least the blog is still up and running.

Which brings to mind http://xkcd.com/349/

40% of OpenBSD installs lead to shark attacks. It's their only standing security issue.

Upgrading Proxmox VE kernel

By , 2009-08-31 16:19

I currently am running this blog from an OpenVZ server managed via Proxmox VE. One issue I had with this setup is that the Proxmox 1.3 installer by default comes with a relatively old kernel (2.6.24), and I want a newer kernel (>=2.6.26, so that I can use my cx18-based TV tuner). Fortunately, Proxmox is just a customized version of Debian Lenny, so I just installed the linux-image-2.6.26-2-openvz-amd64 package from apt, then ran update-initramfs -u and update-grub.

After updating the kernel, however, I was unable to start any of my virtual machines from the Proxmox Web UI. Looking at the system log showed a message about vzctl being 32-bit; problem solved by updating vzctl via apt.

Now I’m attempting to compile v4l-dvb…. fingers crossed!

hg clone http://linuxtv.org/hg/v4l-dvb

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