Fedora 9
To upgrade, I followed the excellent instructions at http://www.gagme.com/greg/linux/f9-tips.php. The key point is to use the ‘preupgrade’ package to sort everything out:

yum -y install preupgrade
preupgrade

This downloads new F9 versions of all the RPM packages you have on your system and then sets everything up so that when you re-boot your machine it will start F9.

It’s an excellent idea, and for me It Just Worked.

KDE 4
KDE version 4 is all rather new. Initially I had version 4.0 installed. The biggest drawback to this version was the absence of the Fuzzy Clock. However, I’m pleased to say that on my first ‘yum update’, my system was upgraded to KDE 4.1, complete with Fuzzy Clock. Whilst version 4.0 was looking a bit rough round the edges, 4.1 is a far more polished affair.

One of the new features (on System Settings, Desktop, General tab) is the ability to ‘Enable desktop effects’, which makes the whole machine much more Mac-like in the prettyness of the desktop. However, I noticed that with this turned on, even when nothing else was running, I was using about 50% of my CPU power just to run the desktop. So I turned that off

The other annoyance in KDE4 was the lack of launch buttons on the panel for my favourite applications. This was really getting on my nerves until I realised that the default ‘tab’ shown initially when clicking on the ‘K’ menu button is the Favourites tab. To add things to the Favourites tab just find the application in the labyrinth of menus on the ‘K’ menu, click it with the secondary mouse button and select ‘Add to Favourites’ from the context-sensitive menu. Now all your favourite applications are just 2 clicks away on the ‘K’ menu button.

UPDATE: Neither KDE 4.0 nor KDE 4.1 can cope with dual screen display systems! I’ve seen comments that imply dual screen configurations are very rare and so fixing the problems is not a priority. Boo : -( See my comments below for details.

Units will convert quantities expressed in one unit in to another unit. Here’s an example:


$ units
2439 units, 71 prefixes, 33 nonlinear units

You have: 12 miles
You want: kilometres
* 19.312128
/ 0.051780933
You have:


So, 12 miles is equivalent to 19.312128 kilometres. OK, that was an easy one to warm up with. Units knows about all kinds of arcane measures and can happily convert between them all. Here’s an example from the man page:


$ units
2439 units, 71 prefixes, 33 nonlinear units

You have: furlongs per fortnight
You want: m/s
* 0.00016630952
/ 6012.8848
You have:


I actually needed to use units to find out my weight in kilos:

$ units
2439 units, 71 prefixes, 33 nonlinear units

You have: 20 stone + 1 lb
You want: kilos
conformability error
127.45946 kg
1000
You have:


My goodness, that’s a large number!

Units should be available in most versions of Unix and Linux - just get a terminal session (telnet or ssh for example) and type in ‘units’. As usual, read the manual page by typing ‘man units’.

Let me give you an example. This web page changes every time I write a new post (admittedly not that often). Rather than periodically checking this page for updates (or, more likely, forgetting all about it until a year later), you can subscribe to it using a feed aggregator or feed reader. Then, whenever I post a new article on this page, it will automatically appear in your feed reader shortly after I publish it.

OK, this may seem to be a bit of a convoluted way to keep up to date with Dr Jan’s Tips From The Top, but when you subscribe to a number of different blogs, the feed reader starts to make a lot more sense.

Below, I’ll go through setting up a feed reader and subscribing to various feeds.

Of course, there are a whole raft of different feed readers available for free download, as well as several which are entirely web-based. Personally, I use Google Reader.

To get started with Google Reader, open a new browser window and navigate to http://www.google.com/reader.

If you already have a Google account, login, otherwise create a new account. Once you have logged in, you should see the ‘Welcome to Google Reader!’ page. You can take the tour or watch the video for further information. Or you can jump right in and click on ‘Get started by adding subscriptions’.

You can select from the bundles that Google offers by default, or, if you have a particular feed in mind, just scroll down the page to the Search and Browse section. In the box, copy and paste this feed address:

http://www.dr-jan.com/tips/feed/

then click the ‘Search for feeds’ button.

Google should find one matching feed, ‘Dr Jan’s Tips From The Top’. Click the ‘Subscribe’ button and, once you see the message confirming your subscription, click on the ‘All items’ link on the top left hand side of the screen. You’ll be taken to the main Google Reader screen with the most recent posts from this blog shown.

As you scroll down the screen, reading the posts, the current post will be highlighted with a blue border. When you move down to the next post, the one you’ve just finished with is automatically marked as ‘read’, so you won’t see that post again in the normal course of events.

You can easily add more subscriptions by clicking the ‘Add subscriptions’ link.

Lots of websites use a small orange icon like this or one of these (shown enlarged for clarity):

to indicate that a feed is available. Normally, you can wrong-click on the icon and select ‘Copy Link Location’ or equivalent command, then paste the results into the Google Reader ‘Add subscriptions’ box.

There are lots of feeds for things other than blogs. For example, BBC News is available as a feed. Check out this page for an introduction to RSS feeds along with a list of some of the feeds available from the BBC.

If you’re searching for a job, most job sites will let you create a feed containing jobs which match your search criteria, so you’ll always know about the very latest jobs as they appear.

Just look out for those small orange icons and you’ll be surprised at what you can subscribe to with your feed reader

Never Eat Chips, Eat Salmon Sandwiches And Remain Young.

My Computer Science teacher taught me this at college

1. Swivel the Blue Oval Ford badge on the front of the car anti-clockwise. It pivots about a point on the left hand side of the badge, so push the right side of the badge upwards. This reveals a key-hole.
2. Use the ignition key to turn the lock fully to the left. The bonnet should pop up slightly.
3. Whilst lifting the bonnet itself, turn the lock fully to the right. This should release the bonnet.

Unfortunately there are no gas struts to hold the bonnet up, you need to deploy the bonnet stay, just like to you used to on old cars

Goodness only knows why this is so tricky to do. Perhaps Ford thought that something valuable or important would be kept under the bonnet. Surely if that was the case, anyone with nefarious intentions could gain access from the bottom of the car, up into the engine compartment?
This has been a Public Service Announcement from Dr Jan.

Cron is normally implemented as a daemon, ‘crond’, which is started automatically when the machine is booted. The cron daemon spends most of its life asleep, but once a minute it wakes up and checks if there are any jobs which need to be started at the current time. If there are, they are started and left to run. Any output from these programs will be captured and sent by email to the user that started the job, unless the output (and the error output) is explicitly redirected on the command line in the crontab file.

You may not have permission to use cron on your system, in which case you will need to (or ask your system administrator to) add your details to /etc/cron.allow and make sure they don’t appear in /etc/cron.deny.

Each user can set up their own personal crontab file, which specifies the schedule and the commands to run.

The crontab file is a plain text file with 6 whitespace delimited fields per line. The first 5 fields specify when to run the commands (which form the sixth field).

Here’s a sample line which removes old temporary files as mentioned in the example above:

0 0 * * * /usr/local/bin/find /tmp -depth -mtime +7 -exec /usr/local/bin/remove {} \;

This is what the numbers at the front of a crontab file mean:

Use a star (*) to indicate all possible values.

So, the example above is executed at 0:00 (midnight) every day.

As you can see, the scheduling scheme is very flexible, allowing everything from once every minute (* * * * *) to once a year (10:00 on the third of January would be represented as 00 10 3 1 *) and almost everything in between.

An important point to bear in mind when using cron is the environment which is used to run the jobs. Cron uses ’sh’, the Bourne shell to run the commands you specify. There is only a minimal PATH statement set up, which is why in the example above the full path name is specified for the find and remove commands.

It can be a good idea to prefix your cron commands with ‘. .profile’ to execute your .profile and set up all your default settings. One thing to be aware of here is that most interactive logins use either ksh (the Korn shell) or bash (the Bourne Again SHell), and there may be commands in your .profile which work fine in ksh or bash but which fail in sh.

The classic example is setting up environment variables. For example,

export PATH=$PATH:$HOME/bin

is valid syntax in ksh and bash, but not in sh. You need to export the variable as a separate step:

PATH=$PATH:$HOME/bin
export PATH

The crontab command is used to configure cron jobs.

Do a ‘man crontab’ for more details

Do be careful when using the crontab command, because if you mistype the switches they can be interpreted as a non-existent filename which will effectively remove your existing crontab.

Unfortunately most of these data were in small files - the largest probably a megabyte or so.

I ran some speed tests. We had gigabit ethernet connecting the 2 boxes on a little used LAN.

I wrote a small script to start 6 copy processes in parallel and another to periodically measure how much disk space had been used on the target machine.

I found that 6 simultaneous scp commands ran at about 15Mb/s (Megabytes per second). scp has the overhead of encrypting the data stream before it is transferred, so I tried plain old rcp as well. That gave me worse results than scp.

Thinking that the large number of small files was slowing things down I tried using tar to batch up the files. I wrote a tiny script to pipe the output of the tar command across to the target machine directly in to a receiving tar process which unbundled the files.

The tar approach almost doubled the rate of transfer to about 30Mb/s.

Here are the tar commands. Note that you’ll need to enable r-commands by creating .rhosts files in the home directories of each machine (remove these after they copy is complete - they are notorious security problems). Note also that, as usual, HP-UX is awkward - whereas the rest of the world uses ‘rsh’ for the remote-shell command, HP-UX uses ‘remsh’. ‘rsh’ is some kind of restricted shell in HP parlance.

box1> cd source_directory; tar cf - . | remsh box2 "cd target_directory; tar xf - "

The first tar command creates a file called ‘-’, which is a special token meaning ’standard output’ in this case. The archive created contains all the files in the current directory (.) plus all subdirectories (tar is recursive by default). This archive file is piped into the remsh command which sends it to the box2 machine. On box 2 I first change to the proper receiving directory, then I extract from ‘-’, or ’standard input’ the incoming files.

I had 6 of these tar commands running simultaneously to ensure the network link was saturated with data, although I suspect that disk access may have been the limiting factor.

Don’t think that because you’re more technical/brighter/don’t really care about the existing data that you’ll be OK.

If you don’t have a back up Murphy’s Law dictates that something disastrous will happen and you’ll lose everything.

If you do have a backup, by the same logic you’ll be fine. Think of it as an insurance policy

First the High Level Overview For Beginners

OK, maybe first we should ask ‘Why do we care?’

IP stands for Internet Protocol. It’s part of the TCP/IP (Transmission Control Protocol / Internet Protocol) network protocol which is used, pretty much, by all computers connected to a network. By network I mean a LAN or Local Area Network used in businesses, or the connection from your computer to your Internet Service Provider (ISP), for example. Even if you use a modem to dial your ISP over a standard phone line, once you’re connected your computer will be using TCP/IP to talk to your ISP’s computers.

To make TCP/IP work, every computer connected to a network must have a unique IP address. IP addresses are usually written as 4 numbers separated by dots, for example, 192.168.0.10. Each of the 4 numbers can be in the range 0 to 255, although 0 and 255 themselves are special values which are not normally used.

Your IP address can be compared to the address of the building where you are now (assuming you’re not reading this on a mobile device outside somewhere). Every building has a unique address, so the post office can deliver letters and parcels to the right destination. Every computer needs a unique address, so that packets of information (like parts of a web page or an email) can be delivered correctly.

More Details For The Interested

For home users, your ISP assigns IP addresses to your computer. If you dial-up, every time you make a connection you are assigned an IP address. When you hang up your connection, that IP address is made available for other callers. If you have a broadband connection then you will have what I’ll call a semi-static IP address. Because your broadband connection is always on, in theory, once you have an IP address you should keep it. In practice, your IP address may change if you power-cycle your cable modem or your ADSL modem.

The system which runs on the ISP’s computers which keeps track of who currently has which IP address is referred to as the Dynamic Host Configuration Protocol, or (more commonly) DHCP. DHCP is normally configured with a pool of IP addresses. When a computer wants to join a network (for example, when you dial up your ISP) it will request a new IP address from the DHCP server. The DHCP server will allocate one of the addresses in the pool and log the details for future reference.
As you can imagine, referring to computers by a sequence of numbers is not a very convenient thing to do (unless you’re a computer), so often as well as an IP address a computer will have a public name. This is the case for most computers connected to the internet. Names are easier for us humans to deal with than IP addresses, and there’s a system in place called DNS (the Domain Name System) which translates IP address to names and vice versa.

This means that rather than referring to 198.63.34.251, I can type www.dr-jan.com into my browser instead - much easier Both methods should work - try typing the IP address directly into a new browser window and you should see a lovely yellow home page

The computer which hosts my web site has a fixed IP address - it will never change, even if the computer is re-booted. This is A Good Thing because otherwise no-one would be able to find my website if it was suddenly using a new IP address. Generally speaking, computers which host websites and other web-based services will have fixed IP addresses, whilst home users and others will have dynamic addresses.

Technical Details For Experts

How you find out what your current IP address is depends on your operating system.

If you are using Windows NT, 2000 or XP, start a command window (Start|Run|cmd or Start|Run|command) and enter the command ‘ipconfig’. ipconfig /all should give you more information.

Windows 95, 98 and probably ME, start a command window as above, but run ‘winipcfg’ instead of ‘ipconfig’ and you should see a handy window appear with all the relevant details shown.

For Linux users, ifconfig is your friend. Unless you’re the root user you may need to specify the full path (normally ‘/sbin/ifconfig’).

For SUN Solaris, ifconfig -a should give you the required details.

HP-UX is awkward, as usual. You’ll need to run ‘lanscan’ to find out what LAN adapters you have, then use ifconfig lan_adapter_name. For example, ifconfig lan0.

Digital Unix uses ifconfig -a.

Footnotes and Disclaimers

I’m not an expert in Windows, so please let me know if you have any updates for the information presented here.

Hopefully my Unix and Linux knowledge is more reliable, although I’m always pleased to receive updates for that too