etbe - Russell Coker

mac vs PC vs Linux

Apple has a series of funny commercials comparing the Macintosh with a PC running Windows. They are very well written and presented. I recommend viewing them for the amusement value (view them here – but you need Quicktime).

Novell has produced a few short parodies of those adverts, they don’t have the same production quality but are well written and not nearly as cheesy as I had feared (view them here). Novell’s ads are in OGG and MP3 format.

Update: A comment pointed me to this site which has other parodies of the Mac adverts. There is quite a bit of bad language and the parodies will offend some people in several ways. But they are amusing and do make some interesting points.

hybrid Porsche

The April 2007 issue of the RACV magazine announces that Porsche is working on a hybrid vehicle. It seems that the award-winning Lexus hybrid vehicle has demonstrated the value of hybrid petrol-electric technology for performance vehicles and that Porsche want to catch up.

The trend seems to be towards all vehicles that are desirable being available in either hybrid or Diesel variants, and we’ll probably see hybrid Diesel vehicles on Australian roads soon.

Trusted Solaris vs SE Linux

Karl MacMillan writes an interesting review of a Sun article about SE Linux. Not only does he correct errors in the Sun article but he also summarises some of the features of SE Linux design and terminology that we use. If you are interested in computer security and want to learn some of the basic concepts then Karl’s review is worth reading.

questions regarding SE Linux

I just received a question about SE Linux via email. As I don’t want to post private messages containing material that’s globally useful I’ll answer through my blog:

> other than strict and targeted policies……other policies like
> RBAC, MCS, Type Enforcement are also there….how are these policies
> implemented

The two main policies are the strict policy and the targeted policy. The strict policy is the earliest and was originally known as the sample policy (but was given the name “strict” after targeted was developed).

The strict policy aims to give minimal privileges to all daemons. The targeted policy aims to restrict the programs that are most vulnerable (network facing daemons) and not restrict other programs (for ease of use). There is currently work in progress on combining those policies so the person who compiles the policy can determine which features of strict they desire.

RBAC means Role Based Access Control. The strict policy assigns users to roles and the role then limits the set of domains that can be entered. For example the user_r role does not permit the sysadm_t domain so a user who is only permitted to enter the user_r role can not perform sys-admin tasks. Like many terms RBAC is used in different manners, some people consider that it means direct control by role (EG role user_r can not write to /dev/hda), while SE Linux has a more indirect use of roles (role user_r can not run programs in domain sysadm_t or any other domain that allows writing to type fixed_disk_device_t – the type for /dev/hda). You may consider that the strict policy supports RBAC depending on which definition of the term you use.

Generally the targeted policy is not considered to support RBAC, although if you consider a role to merely be a container for a set of accesses that are permitted then a SE Linux domain could be considered a in the RBAC sense. I don’t think of targeted policy as being a RBAC implementation because all user sessions run in the domain unconfined_t which has no restriction. I think that to be considered RBAC a system must confine user logins.

Type enforcement is the primary access control mechanism for SE Linux. Every object that a process may access (including other processes) has a type assigned to it. The type of a process is known as a domain. The system has a policy database which for every combination of domain, type, and object class (which is one of dir, file, blk_file, etc – all the different types of object that a process may access) specifies whether the action is permitted or denied (default deny) and whether it is audited (default is to audit all denied operations and not audit permitted operations).

MCS is a confidentiality protection mechanism where each file has a set of categories assigned to it. The set may be empty, may contain all 1024 categories, or any sub-set. Each process has a set of categories that determines which files it may access. File access is granted if Unix permissions allow it, if the domain-type model allows it, and if MCS allows it (on an MCS system). I have just had an article on MCS published in Linux Journal.

MCS is an optional feature for people compiling Linux from source or for distribution vendors. For Red Hat Enterprise Linux, Fedora, and Debian the decision was made to include it, so the strict and targeted policies for those distributions include MCS.

There is another policy known as MLS. This is a policy build that comprises the strict policy plus Multi-Level Security. Multi-Level Security aims to give the highest confidentiality protection and comply with the LSPP (Labeled Security Protection Profile – roughly comparable to B1) Common Criteria certification. It would be possible to build a targeted policy with MLS but that wouldn’t make sense – why have the highest protection of confidentiality with anything less than the highest protection of integrity?

As for how the policies are implemented, I’m not about to write a tutorial on policy writing for a blog post, I’m sure that someone will post a link to a Tresys or Fedora web page in the comments. ;)

> there r some packages of linux in which some changes has been made
> to support linux……for eg:- coreutils, findutils

That is correct. Every program that launches a process on behalf of a user at a different privilege user (EG /bin/login, sshd and crond) and every program that creates files for processes running in different domains (EG logrotate creating new log files for multiple daemons) needs to be modified to support SE Linux. Also ls and ps were modified to show SE Linux contexts as well as the obvious programs in coreutils.

> ‘Z’ is the new thing that have been added to most of the
> utilities……wherever I search I get the changes made only in few
> utilities like ps, mv, cp, ls
>
> Can u help me by giving all the changes made in each of the utilities…..

Unfortunately I can’t. This has been identified as an issue and there is currently work in progress to determine the best way of managing this.

death threats against Kathy Sierra

The prominent blogger and author Kathy Sierra has recently cancelled a tutorial at a conference after receiving death threats.

Obviously this is a matter for the police to investigate – and the matter has been reported to them.

It’s also an issue that is causing a lot of discussion on the net. The strange thing is that a large portion of the discussion seems based on the idea that what happened to Kathy is somehow unusual. The sexual aspect of the attacks on Kathy is bizarre but campaigns of death threats are far from unusual in our society. The first post I saw to nail this is the I had death threats in high school blog entry. Death threats and campaigns of intimidation are standard practice in most high schools. After children are taught that such things are OK for six years straight it’s hardly a surprise that some of them act in the same manner outside school!

But I don’t expect anything to change. Columbine apparently didn’t convince anyone who matters that there is a serious problem in high-schools, I don’t expect anything else to.

I can clearly remember when I first heard about the Columbine massacre, a colleague told me about it and explained that he barracked for the killers due to his own experiences at high-school. While my former colleague probably had not given his statements much consideration, any level of support for serial-killers is something to be concerned about.

This is not to trivialise Kathy’s experience. But I think that discussion should be directed at more fundamental problems in society instead of one of the symptoms. If the causes are not addressed then such things will keep happening.

Xen and eth device renaming

Recently I rebooted one of my Debian Xen servers and suddenly all the Ethernet devices which used to be eth0 in the domU’s became eth1.

vif = [ ”, ‘bridge=xenbr1’ ]

I used to have the above as the interface definition and for domU’s that had only a single interface that worked well (if there is only one interface then it should be eth0). However in a recent etch update this changed, so I had to use ifrename as documented in my previous blog post. It’s annoying when things break because a reasonable assumption which previously worked suddenly stops working.

Even if the bug in question (if it is regarded as a bug) is fixed I’ll keep using ifrename, it doesn’t do any harm.

Update: I have changed my Xen configuration to use fixed MAC addresses which seems to be a better solution than using ifrename. See the Wikipedia page about MAC addresses for information on how to choose them. I’m currently using manually assigned MAC addresses from the range 00:16:3e (which is assigned to Xen).

Save Babe

There’s an advertising campaign at the moment opposing cruel treatment of pigs, the web site is at http://www.savebabe.com/ . They have rented advertising space at train stations to publish the URL.

One thing that they don’t mention is the health issues related to factory farming. It makes sense to concentrate on one message at a time and they are concentrating on animal cruelty. But probably more people will be concerned with the risks of disease, parasites, and anti-biotic resistant bacteria present in meat produced from the factory farms.

Also wild boar tastes better!

google-bank

Currently many people have Google advertising on their web sites, it may even be that a majority of the serious Internet users host Google advertising. Given that Google is already writing a cheque every month to many people, it wouldn’t be difficult for them to change the amount in response to a funds transfer request. Depositing a cheque in a foreign currency can incurr $25 in bank fees (that’s what the Commonwealth Bank of Australia charges me), this is a great impediment to international trade in small values. When Google already has an office in a country and writes cheques in the local currency it would be very easy to have that cheque include funds transfers too.

One significant advantage of Google payments would be the fact that Google doesn’t write cheques for less than $100, so someone who earns $2 per month through Google adverts will be waiting a long time before they get a cheque – but if someone has an item that costs a small amount of money (EG an online service that costs a few dollars a month) then the user would be enticed to use it.

Currently many people don’t place Google adverts because they believe that it would take them an unreasonably large amount of time to reach $100US. But if they could spend the money in small increments on other online services then it would be more enticing.

It seems to me that Google is the only organization that is both capable of running an International online small-payments system and which would be trusted by most people.

If you like this idea please post a comment.

images for a web site

When I first started putting pictures on my web site I used to delete the originals (at the time I only had a 3.2G hard drive in my main machine and used CDs for backup so I didn’t feel inclined to waste too much space). The problem is that I optimised the images for viewing on displays of the day (when 1024×768 was high resolution and I tried to get pictures down to 800×600 or less whenever possible). Also the program I was using at the time for scaling the images didn’t do it nearly as well as the Gimp does now.

Now when putting pictures on my web site I keep the original JPEG’s in a safe place so that if there are future changes to common display technology, net connection speed (particularly the speed of my server) or of technology for scaling and compressing images then I can re-do them to get a better result.

When saving images with Gimp I enable “Advanced Options”, this allows me to set a floating-point DCT method this saves about 400 bytes on disk and apparently gives a better image quality too – it’s not noticably slow on a Pentium-M 1.7GHz so they should probably make it the default. The next “Advanced” option to change is to turn off “Save EXIF data” (saves 1.9K) and “Save thumbnail” (can save almost 5K depending on the image).

The next thing to do when saving a JPEG is to enable the “Show Preview in image window” setting. This allows you to adjust the image quality while seeing the resulting image as well as the size, so you can determine which combination of file size and image quality is best for you. This is much easier than saving
a file and then running an image viewing program to inspect it!

As an aside, it would be convenient if the Gimp would reposition it’s “Save as” dialogue to not occlude the image window and would enable the preview option by default on machines with reasonably fast CPUs.

power saving

Adrian von Bidder made an interesting post in response to my post about Spanish wind power. He correctly points out that power sources that have seasonal variations and which may vary during the course of a day can not be used as the sole power source.

The ideal design would be to have wind power stations that are designed to have a peak power that is greater than the expected use for the country. Then when wind power is slightly below peak the entire use for the country could still be satisfied.

There are a number of power sources that can quickly ramp up, this includes hydro-electric and gas-fired power stations. Such forms of power generation could be used as backup for when wind and solar power are limited. Incidentally one thing to note about Solar power is that it is most effective during the day in summer – which is when there is the highest demand for electricity to run cooling systems. There is also an option for having the sun heat up rocks which can be used for generating electricity at night or at periods of peak demand. So eventually we could have all our energy needs supplied by solar and wind power.

If wind power was designed to exceed the demand at windy times there are a number of ways that it could be used. The first thing to do is to implement billing systems that vary the cost according to the supply. This information could be provided to customers via X10 (or a similar technology). Home appliances could take note of this information and perform power-hungry operations when it’s cheap. Your freezer could cool itself to -30C when electricity is cheap and allow the temperature to rise to -5C when it’s expensive. You could program your washing machine to start when electricity becomes cheap – usually a few hours delay before starting the washing is no inconvenience.

Ideally home power generation from solar and wind sources would be used. There is significant loss in the power lines that lead from power plants to the consumer, so there are efficiency benefits in generating power locally. A wind turbine for a home will give highly variable amounts of power, and the electricity use of a home also varies a lot. So batteries to store the power are required. When you have local battery storage you could use your batteries to power your home when electricity is expensive and use mains power when it’s cheap. Also if it was possible to feed power back to the main grid then home battery systems could be used to help power the main grid at expensive times (if the electricity company reimburses you for putting power back in the grid then you want such reimbursement to be done at the highest rate).

Adrian also mentioned turning devices off when leaving home. It is common practice in hotels that when entering your room you will insert your key in a holder by the door which acts as a master switch for all lights and some other electrical devices (such as the TV).

This same idea could be adopted for home use, not based on key storage (although this would be an option) but instead on a switch near the front door. Push a button and all lights turn off as do human-focussed appliances such as the TV and DVD player turn off (not the VCR), etc. There could also be a night option which would turn off the TV, DVD player, and most lights. Obviously at night you want bedroom and bathroom lights to still work but many things can be turned off.

This is all possible with today’s technology, small changes to usage patterns, and spending a little more money on technology. Currently you can get a basic solar power system for your house for about $10,000. That isn’t much when you spend $300,000 or more buying the house!

etbe – Russell Coker

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