Butter Mountain | The unwanted stock pile.

Redundant bonding of wireless and wired interfaces in Ubuntu.

Posted on September 14, 2007 by iain

Recently while attending a networking course which covered redundant multipathing for high availability systems I got to thinking – could this be applied to my wired / wireless network at home? The end result being that removing the wired network from my laptop by unplugging the cable would instantly fail over to my wireless connection. I’m sure many people are thinking “but gnome network manager already does that” well, not quite.

With redundant bonding or multi-pathing both interfaces are connected to the same network and put into a special group. These interfaces are constantly connected to the network and are ready to work, however only one of them is active at any one time. Should the active interface fail (such as a network cable being removed) the mac address, ip address and all other configuration is almost instantly assigned to one of the other available network interfaces. This allows you to continue working as if nothing had happened, songs playing from network shares will continue playing, instant messenger conversations will continue to work, downloads will not be interrupted… the list goes on.

It turns out that under Linux this works incredibly well, read on for details.

Requirements.

In terms of networking you must have your wired and wireless networks on the same physical network segment, in this post I am also assuming that your wireless network is setup and that you have knowledge of networking.
As for packages you will need to install the ifenslave package under ubuntu.

# apt-get install ifenslave-2.6

Step One.

Warning: if you follow the steps I’ve included here, reboot and anything goes wrong, I accept no responsibility – thanks.

Under Linux high availability and link aggregation is handled by the bonding module, this can be enabled by adding the following line to your /etc/modules configuration file.

bonding mode=1 miimon=100 downdelay=200 updelay=200

This will load the bonding module upon next boot, however, it can be loaded at any time using the modprobe command the options are as follows.

mode=1 – This enables the active backup mode, this will provide link level redundancy but it does not allow for any kind of link aggregation.

miimon=100 – This enables link level monitoring of the connection (the default value is 0 – which disables link monitoring). The value passed is the frequency in milliseconds that the link is checked. Link level monitoring only takes into account the physical connection, not if the network is correctly configured or not.

downdelay=200 – This is the delay in milliseconds before the link is marked as failed, it must be a multiple of miimon

updelay=200 – This is the delay in milliseconds before the link is marked as active, it must be a multiple of miimon

Step Two.

Next the bonding interface (bond0) must be configured, this can be done in the /etc/network/interfaces file an entry such as this needs to be added:

auto bond0
iface bond0 inet static
address 192.168.1.34
netmask 255.255.255.0
gateway 192.168.1.24
broadcast 192.168.1.255
post-up ifenslave bond0 eth0 eth1
post-up echo “eth1″ > /sys/class/net/bond0/bonding/primary
pre-down ifenslave -d bond0 eth0 eth1

The network address, netmask, gateway and broadcast should be configured for your network. This is the one single address that your machine will be known as, assuming that one of the connections to your laptop is available. You should be able to use dhcp to configure this interface, however I have chosen a static address.

‘post-up ifenslave bond0 eth0 eth1′ – This line assigns my wired (eth1) and wireless (eth0) interfaces into my failover group bond0. You should replace these with the interfaces you want to use.

‘post-up echo “eth1″ > /sys/class/net/bond0/bonding/primary’ – This line specifies a primary slave, that is if this interface is available it will always be used in preference to the others. In this case eth1 is my wired interface, this ensures that when I return to my desk and plug my network cable back in I will be using the faster ethernet network and not my slower wireless.

‘pre-down ifenslave -d bond0 eth0 eth1′ – This line removes the eth0 and eth1 interfaces from the bond group when networking is stopped.

Step Three.

Now reboot for the settings to take effect. It is of course possible to do all of this without rebooting, one would simply perform the following steps:

modprobe the bonding driver
ifconfig the bonding interface
add the default route for the bonding interface
ifenslave the network devices
set the primary bonding interface

To Test that everything is working simply ping a host on your local network then once its going unplug the wired interface it should fail over to the wireless interface without dropping any packets. You can then re-insert the network cable and instantly switch back to the wired interface.
Help, its not working.

I had a few problems getting this working, firstly ifenslave would assign the bonding interface the mac address of my wired interface. As part of my wireless network security I have mac filtering enabled, however, only the mac address of the wireless card was allowed. Adding the mac of the bonding interface to my mac filter list cleared up that problem.

My other problem involved gnome network applet, I believe that this process is called nm-monitor. This would attempt to reconfigure my wireless network or wired network whenever I removed the network cable to my laptop. This appeared to prevent the failover from working as quickly as it should have. killing off the nm-monitor fixed this little issue.

I’ve now been using this for roughly two weeks without any issues, being able to unplug my laptop and take it to another room of the house without having to even consider whats going to happen to my network has been a real step forward.

Posted in hardware, Linux, networking | 2 Comments

When Good Hard Drives Go Bad

Posted on May 3, 2007 by iain

Picture the scene, you return to your system and casually attempt to create a new file on one of your disks. Permission Denied. What?

Check you’re logged in as the correct user – check
Check that the user has write permissions – check

Following this you start to get a sinking feeling, something is not right. In fact, something is very wrong but you don’t know what that is just yet. Although, the situation feels vaguely farmilar. Without recalling why you decide to check if the partition you’re attempting to write to has been mounted read only. It has, your mind races and you check /var/log/messages for the worst.

ide: failed opcode was: unknown
end_request: I/O error, dev hdd, sector 61866003
Buffer I/O error on device hdd1, logical block 30933001
hdd: dma_intr: status=0×51 { DriveReady SeekComplete Error }
hdd: dma_intr: error=0×40 { UncorrectableError }, LBAsec= 63963157, high=3, low=1460081, sector=65011733

And now you realise why this felt so familiar, its because the same thing has happened to one of your disks at the beginning of summer three years in a row. You really should have made backups by now.

I’m sorry to say that this is a true story, three different branded disks in different systems in different houses all in different conditions. The only common factor is that these disks all ran 24/7 and were used as a ‘media repository’. Having been in this situation before I would like to share my experiences of simple disk recovery under Linux.
Step One.

Unmount the faulty disk (stop reading this, do it now). Forget about reading from it, forget writing to it and whatever happens do not fsck the faulty disk. Running fsck against a disk with physical errors will only make the problem worse. I recommend that you disconnect the disk and store it somewhere safe.
Step Two.

Buy/locate/steal/borrow a replacement disk, as you’re going to need somewhere to copy your data to. You should then connect both disks, you new disk and the faulty disk to your system. If possible try to get them on separate IDE buses, I’ve had one disk fail which created IDE bus resets when reading from it. This had a negative effect on all disks on the same IDE bus (including the good disk I was copying to). Format your new disk and check that its working, do not store anything important on it just yet as it will be overwritten.

It should also be noted that if you have a disk or array which is already in-use but has enough free space available, then you can write an image of your damaged disk to this space. The disk image can then be fscked and mounted via a loop back mount. The exact details of this method are not covered here but it should be easy to adjust the methods described here.
Step 3.

Install GNU DD Rescue onto your system ( http://www.gnu.org/software/ddrescue/ddrescue.html ) the package name under Debian / ‘bunty (Ubuntu) is gddrescue. This is possibly one of the most useful data recovery tools I’ve used. It is dd designed with data recovery in mind, it will allow you to read directly from the disk ignoring any errors which may exist in the file system. The website lists its most important features but most importantly to us its very easy to use and fully automatic. Once you’ve read the manual page for dd rescue its time to start on recovering your data.
Step 4.

Make sure that both your old faulty disk and your new disk are unmounted, once that is done invoke dd rescue.

# ddrescue /dev/hdd1 /dev/hdc1 /logfile

In this example, /dev/hdd1 is my old faulty disk (the source) and /dev/hdc1 is my new disk (the target) the /logfile will create a log file which dd rescue can use to resume its recovery should you need to stop it for any reason. This will take some time so sit back and wait, the output from dd rescue is very clear. It will keep you informed as to how much data it has copied, how much is unreadable and how many errors have occoured.

For my most recent disk failure on a 250 Gigabyte drive ddrescue was able to read all but ~2 Megabytes of data. Which is really quite fantastic when you consider that with the faulty disk mounted read only I was unable to copy any files without producing hundreds of errors.
Step 5.

The moment of truth, dd rescue has read all it can read and now its time to fsck the new disk.

# fsck -C /dev/hdc1

This will run fsck with a handy progress bar, If you’re very lucky fsck will complete without complaining and you have successfully rescued all of your data. If you’re not so lucky (as I have been this time) you may have suffered some fairly nasty file system corruption, fsck will go through asking you if you would like to fix the errors. You should make a note of which files have gone and let fsck do its thing, there may be better ways to handle this, if there are I would love to hear them. If you have only suffered damage to the file system structure and your actual data files are okay then you will end up with a load of files in the lost+found directory. Simply put these are files which exist on disk but no longer have a file name (and other things) associated with them, so fsck will move them into the lost+found directory.
Step 6.

Thats it really, you should have most or all of your data back, unless you’ve been really unlucky. Now is the time to create a backup plan, do it now while the fear is still in you. Otherwise six months down the line you’ll be thinking to yourself, “nahh disk failure wont happen to me (again)”.
It should be noted that there are variations on this method, if anyone knows of any better ways to handle a failed disk please let me know, I’d love to know if there are any steps or tools I’ve missed out upon.

Posted in hardware, Linux | 1 Comment

Tarte Aux Iain

Posted on March 28, 2007 by iain

Introduction

Its Sunday afternoon here in Paris, I’m feeling what could be described as boredom mixed with hunger, boreger no hungdom maybe. When I feel like this it is often time to cook something. As it is Sunday, the shops are mainly closed so I will have to get creative with what I have in the fridge.

I may subconsciously plan for afternoons like these as I appear to have all of the ingredients to make “Tarte aux Iain” or “Iain’s Tarte”. If you wish to make Tarte aux Iain you need the following ingredients:

Ingredients

2 x Oeufs De Poules (Eggs of a Chicken)
1 x Pate Brisee (Short Crust Pastry)
3 x Champignon de Paris (Button Mushrooms)
1 x Lait (Deme-ecreme UHT) (Semi Skimmed UHT Milk)
1 x Emmental Rape Fromage (Emmental Ripe Cheese (grated))
1 x Creme Fraiche (Creme Fraiche)
1 x Lardons de Nature (Little bits of bacon chopped into cubes)
1 x Pivoron Vert (Green Pepper)
Pepper, Herbs & Garlic

This serves roughly 2 – 4 people depending on the size and appetite of the people.

Of course, you don’t actually need all of these to make your own Tarte (Tarte Aux Vous). The base ingredients are the eggs, pastry, milk, cheese and creme fraiche. As for everything else, I recommend you include whatever you can find in your fridge.
Through mis-communication I have made tarte using Natural Yogurt instead of Creme Fraiche, it was an interesting experiment but not one that I would recommend you repeat. It should also be noted that you can use non UHT milk.

Utensils

1 x Frying Pan
1 x Baking Tray
1 x Tiny French Electric Oven with built in hobs.
1 x Mixing Bowl (not pictured)
1 x Whisk (not pictured)

The tiny electric oven can be replaced with a larger standard oven if a tiny French electric oven is not available. Of course this detracts from the authenticity of the Tarte. The Oven should be pre-heated to roughly 220 Degrees oC.

The Oil

In the above picture you can see my oil, its called “4 Huiles” or “4 Oils” in English, it is advertised
to have the following four properties.

Forme – Fitness and Health
Equilibre – Balance, Equilibrium
Bien-Etre – Well-Being
Plaisir – Pleasure

If only the oil in England had these properties we would all be much healthier, balanced and pleasured. From that list I think it should be obvious why I have chosen the 4 oils, you can of course use whatever type of oil is available (I’d actually recommend a nice olive oil if you have one available). The oil is to be used when frying the ingredients later on.

Vegetable / Meat Preparation

All of the vegetables and meat that you plan to put in your Tarte should be chopped in into small cubes. As my Lardons Au Nature come pre chopped I wont need to chop those. The Vegetables should look something like this when you’re finished with them.

The Tarte Mixture

This is relatively simple to create, you are aiming to create a liquid which has just moved from being thick to one which is runny. As I’ve never made this using measurements you will just have to do this by eye.

Step one, crack two eggs into the mixing bowl and add your creme fraiche. I put in roughly two and a half mounded dessert (large) spoon fulls into the mixture here.

Step two, add the milk, again how much is to be done by eye. Remember that you need to fill your baking tray with enough of this mixture that it just covers your chopped meat and vegetables. You can add some pepper and seasoning here to taste if you wish.

Step Three, Whisk it all up! There should be no lumps of creme fraiche or egg when you are finished just a white runny mixture.

Cook The Vegetables and Meat.

All of the ingredients should be pre-cooked before you put them in to your tarte, I find it easiest to fry everything (making use of my 4 oils) until they’re done. If you like you can also throw in some pepper and herbs here, I believe I also put some chopped garlic into
this tarte.

Preparing The Tray

Step One, Line your tray with something to stop it from sticking, I have used butter but you could also use grease proof paper. Now take your round short crust pastry and attempt to put it into a rectangular pan (not as easy as you might think). Finally prick the pastry all over with a fork.

Step Two, Put your vegetable and meat mixture into the tray, spread it as evenly as possible throughout the tray.

pastry_and_stuff

Step Three, Pour your tarte mixture that you pre paired earlier into the tray.

pastry_stuff_milk

Step Four, Cover everything in the tray with massive amounts of grated cheese, once this is done your tarte should be ready for the tiny electric oven.

ready_for_oven

The End Product

You should put the tarte in the pre-heated oven for roughly 40 minutes, Generally you can judge when the tarte is ready by the colour of the cheese on the top. If its gone golden brown all over then the tarte should be ready.

Your end product might look something like this, although this picture does not do it justice.
end_product_tarte

The tarte can be eaten hot or cold, it works well with salad and boiled new potatoes. Enjoy!

Posted in Cooking, France, nontech | Leave a comment

Fifty Things an Englishman may learn about Paris (or France)

Posted on March 17, 2007 by iain

After living in Paris for over six months there are many new things that I have had to learn. The language being only the most obvious but there are far more interesting oddities which slowly expose themselves to you over time. The author Stephen Clarke has written several fantastic books on this subject which I highly recommend. All of the points in this list are related to something I have experienced while living here, its far from a definitive guide but its at least a start. With that being said, onto the list which is in no particular order.

Traffic Lights are merely a suggestion
Pointing at drivers is an effective way to make them stop
Queuing is for people who have time to waste
An Englishman should learn French
Speaking bad French is worse than speaking English
Bribery is the most effective way to get things done
Shrugging is a highly effective form of communication
Being on time for a (work) meeting is like turning up to a party two hours early
Meetings are not for working, they are a chance to see your friends
Deadlines, schedules and time have no bearing on anything – ever
9am often means 2pm or 2:45pm if it was a nice lunch
The first hour of the day is devoted purely to greeting everyone in the office
The third hour is devoted to a coffee break
A good lunch should last until 3:30pm
Public transport in Paris is outstanding if not a little crowded
The metro is practically free
Going outside Paris by public transport is an ill founded idea
Alcohol in supermarkets costs very little
You may need a small loan to buy a round of drinks in a Pub
Everyone must go on holiday at the same time
Street markets are fantastic, though a little off putting at first
After eating a ‘well done’ steak you should still be able to mop the blood up on your plate with some bread
A rare steak is cold (read: raw) on the inside with the outside lightly seared
Steak Tartare is available in all restaurants which serve burgers
If someone on the street randomly asks you if you speak English say ‘non’
‘Quick’ is not a French fast food restaurant, its Belgian, the French do not have ANY fast food restaurants
Nearly all McDonald’s restaurants in Paris have free wifi internet access
The Belgians are to the French what the Welsh are to the English
The only good Belgian film is ‘Man Bites Dog’
Indian food in France is generally not spicy
Walk 500m in any direction and you will end up next to a metro station
Beware of tourists for they travel in packs
The Montparnasse Tower and the Effiel Tower can be used as navigation beacons when the metro has closed and you are very drunk.
You are unlikely to witness a single act of physical violence while in Paris
Most English kitchens are large, so large in fact they have an entire room devoted to them.
The inefficiency of business is a point of national pride
Legal contracts in France are incredibly complex
Train doors may open before the train has stopped
It is very easy to wonder onto a construction site in the middle of the street
Construction workers appear to follow no safety rules at all
Dogs crap everywhere
There is an army of men in green who wash away the dog turds
Most French over-the-counter drugs are double the strength of the English name brand equivalent
Christmas decorations often last until February
There is very little Christmas music in shops
French popular music is beyond awful (Diams must be forced never to produce any more music)
Real books do not feature cover illustrations
Not topping up your mobile phone results in you losing your number
Just because you have been seated in a restaurant does not mean you will get served.
Waiters are not referred to as ‘GarÃ§on’

Maybe some more another time…

Posted in France, nontech | Leave a comment

Console gaming on a remote X display

Posted on November 24, 2006 by iain

I have recently ended up in a situation where creating something like this (see diagram) would allow me to play my Game Cube on my laptop display before I finalise my purchase of a nice new LCD display for my desktop system.
Game Cube -> Tv Card -> Linux Box (no display) -> 100Base-t Network -> Laptop (with display)

Playing a console game over a remote X display is slightly more challenging than simply watching TV. With TV you can capture your video and audio input, compress it, send it over the network in a nice format and decompress it at the other end. Sure, you’ll be watching TV that is maybe one second to a minute behind whats actually being broadcast but its in sync and it looks good. If you’re attempting to play a game in a similar fashion even 500ms (1/2 a second) delay would make most console games totally un-playable, with this in mind I set about console gaming over remote X with ssh.
It should be noted that:

While attempting this I had no access to the internet, just to whatever documentation came with my debian / ubuntu installs
My desktop runs debian testing and my laptop runs ubuntu edgy eft
If you just want the solution, skip down to Attempt 4.

Attempt 1 – tvtime

Usually when playing Game Cube on a local display attached to my desktop I use a fantastic application called tvtime, To run this I SSH’ed from my laptop to my desktop with X display forwarding and compression enabled:

iain@laptop ~> ssh -X -C -o CompressionLevel=9 desktop

iain@desktop ~> tvtime

Unfortunately for me tvtime does not appear to work via X display forwarding, it appears to be looking for an xvideo port to connect to and fails upon startup, most likely tvtime was not designed for this.

Attempt 2 – xawtv

Xawtv is a tried and tested linux tv viewing tool, its almost

guaranteed to work and it did:

iain@laptop ~> ssh -X -C -o CompressionLevel=9 desktop

iain@desktop ~> xawtv -remote