Long-term Memory

I think I can skip the buildup on why backups are important and I’ll focus this post on the “how”. There are a lot of ways to make backups. Obviously some are better than others; in this post I’ll just explain how I do my backups.

The script I use was designed with the following items in mind:

• The storage medium is a hard drive. This has some advantages like random-access which can be used.
• Storage capacity should be as small as possible; differential and/or incremental backups are almost unavoidable in this.
• The backups should be pulled from the server. This way you know when a server is behaving strangely. If you push your backups and the server has a bad day, he won’t tell you that he forgot his backups!
• Since the backup contains sensitive data (eg SSL private keys, /etc/shadow), the network transfer should be encrypted.
• The backup needs to be taken as root. This is the only way to ensure that all files could be read. (Yes, technically you could use specific capabilities instead of root)

Continue reading ‘Backup script – incremental snapshots’ »

I’m a bit paranoid when it comes to security. For example, I don’t allow passwords to log into my computers via SSH but use RSA keys instead. Besides added security (there is no password to guess), it has a lot of other advantages as well. I normally run an ssh-agent (both on linux and Windows) which caches my credentials so I can log in without password.

On my desktop system, this was automatically secure against theft. Since the key is stored in RAM (or encrypted swap), it is flushed the moment the computer looses power. Since it was a desktop system, it’s fairly safe to assume that the power will be cut when someone steels my computer.

On my new MacBook Pro, things are a bit different: most of the time, my notebook is in standby and has an integrated UPS (its battery). So I was looking for something to get me the same security.

Continue reading ‘Securing SSH Agent on Mac OS X’ »

Last Saturday, I got myself a new Unibody MacBook Pro. However it crashes once a day… By crashing I mean either a full freeze (mouse pointer unresponsive, closing the lid unresponsive, ambient-light sensor unresponsive) or a kernel panic. I didn’t find how to reproduce this issue, but in the last 4 days it has crashed once every single day.

Things I already tried:

• Ran the Mac Diagnostics (Apple Hardware Test), both the standard and extended tests; it reports “everything OK”
• Ran the Mac-ified memtest86+ for more than 9 hours; it reports “everything OK”
• Erased the NVRAM and erased and reinstalled Leopard (and all software updates); the problem persists

Just for the record: The only software installed is Leopard, iStat Pro and Adium.

Needless to say, I’m not really happy with the Apple hardware. After trying the above steps myself, I called Apple Care with this issue. I must admit, the guy on the phone was very helpful and recognized that I tried pretty much everything I could to solve the problem. He gave me an incident number and told me to return the MacBook Pro to the store, since the laptop is only 4 days old…

Continue reading ‘MacBook Pro’ »

Place: Home garden
Flights: 1
Time flown: 0h25 (cumulative model timer: 2h10)
Heli battery recharged with: 1714 mAh
Tx battery recharged with: not recharged

Comments:
Demonstration for the family. Flew for 7 minutes or 68%, guestimating on the charged-in capacity.

Right after the flight, the battery was warm (I’d guess somewhere 35-40°C), the engine was fairly warm (around 50°C) and the ESC was hot (60-70°C). The temperatures are measured with my fingertips, so they are very accurate…

Since I’m a fairly curious and technical kind of person, I needed to know all the gory details of exactly how helicopters fly. Here is what I found out:

• Very nice series (part 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11) by Colin Mill on different aspects of model helicopters. Subject goes from servo linkage through Bell-Hiller ratios. The articles are fairly old (1995-1996) but the physics are still the same!
  
• Dynamic Helicopter Aerodynamics describes all the aerodynamic effects on (real-size) helicopters. Most of these effects also apply to model helicopters, although some become less important. Covered topics go from basic airfoils to vortex ring state and dynamic rollover.
• The same site also has a Dynamic Flight Maneuvers section, bringing the aerodynamics into practical situations such as ridgeline landings or plain simple hoovers.

Place: Home garden
Flights: 1
Time flown: 0h08 (cumulative model timer: 1h45)
Heli battery recharged with: 1185 mAh
Tx battery recharged with: 1021 mAh

Comments:
First real flight. One of the things I need to calibrate is the flight duration of my battery. I flew 5m55s on this battery and it was recharged with 1158 mAh. Extrapolating this gives an max flight time of around 12 minutes and 28 seconds.

I got myself a new RC helicopter. It’s an electric one so I can fly indoors.

Here is the partlist and some basic specs:

• Thunder Tiger miniTitan E325
  624mm long, 120mm wide, 210mm heigh, 728mm main rotor diameter, 156mm tail rotor diameter, 750g weight
  manual [local copy]
• Thunder Tiger Ripper OBL Series Helicopter Brushless Motor 29/35-10H (mine came with the miniTitan kit)
  3500rpm/V, 20A continuous, 30A.60s burst, 12 stator windings, 8 permanent magnets on the (outrunner) rotor
• ACE R/C Brushless Motors Speed Control ESC BLC-40 (included in the kit as well)
  40A continuous, optional governor function
• 3x Hitec HS 65 MG (more detailed specs)
  4.8 – 6V input voltage, 60° in 0.14s (4.8V, no load), 1.8kg.cm stall torque
• Futaba S-9257 (more detailed specs)
  digital, 4.8V input voltage, 60° in 0.08s (no load), 2.0kg.cm stall torque
• R319DPS receiver – 35MHz band
  1024PCM receiver, 8 proportional channels, 1 digital channel
• Futabe GY401 Gyro
  Solid state gyroscope with Heading Hold (AVCS)
• FLIGHTPOWER 3s1p 25C 2500mA 11,1V
  Continuous discharge 25C/62.5A, Climbouts 35C/87.5A, Max burst 50C/125.0A
• Flightpower V-balancer
  LiPo balancer for up to 6s packs

Continue reading ‘The new toy: mini Titan E325’ »

Place: Halle
Tanks flown: 3
Time flown: 0h56 (cumulative model timer: 29h52)
Rx battery recharged with: 728 mAh
Tx battery recharged with: not recharged
Glow heater battery recharged with: 462 mAh
Starter battery recharged with: 133 mAh

Comment:
Another beautiful autumn day (which are fairly rare in Belgium), although the sun was hanging low. Naturally, I was able to pilot my heli straight into the sun. Apart from the black spot in my vision the next 3 minutes, nothing got damaged in the process.

Tried and succeeded in a full auto-rotation with 0% engine power (previous attempts where with some power). Turns out that it isn’t too much different from 15%. Even at 15%, the engine is hardly engaging the clutch so it barely provides power.

Recently, I have been “upgrading” my blog by including some nice WordPress plugins. Some of them are barely noticeable, others get some sidebar-real-estate.

Here is a list of plugins I currently use:

• Akismet: Keeps the spam out of the comments
• Add From Server: Allows me to upload files in batch using SFTP and add them to the media library later
• Attachment Extender: Allows an attachment (image, video, file) to be updated. Normally you need to delete/re-add the item
• Better Blogroll: Displays a list of random links in the sidebar
• Blogroll Links Page: Generates a page with all links from the database; although I hacked in a little bit of functionality to have empty categories suppressed and to display the category description.
• CyStat: Gathers statistics on page visits, incoming referrers, most popular posts, …
• FLV Embed: The embedded flash player in some posts (eg this one)
• Search Unleached: Adds search highlighting to the pages; search through comments as well

I’m still looking for (a) plugin(s) to accomplish some things:

• Basically get the “Media Library” page from the admin-interface onto the blog itself. A bit like the Blogroll Links Page plugin does for links.
• Some plugin/hack/extension that allows the “Media Library” to be organized by tags and/or categories. Technically this isn’t a big task: the database stores attachements just the same as it does posts, so it’s only a user-interface thing.
• Search through the captions and descriptions of the “Media Library”

If anyone knows of a plugin to solve these issues, please let me know.

Update 2008-10-26

I basically wrote my own plugin to accomplish what I was looking for. It’s far from perfect, but it gets the job done.

Update 2009-06-17

I replaced CyStat with AWStats; it’s not a WordPress plugis, but gives me much more information. I also removed Search Unleached, since it wast not compatible with WordPress 2.8 (at the time of the descission).

Another update

I added Broken Link Checker. It’s a great plugin that routinely verifies all your links and notifies you when they’re broken.

I often need to work with IP addresses and IP subnets. Somehow humans are not very good at binary arithmetic, so converting from 255.255.192.0 to /18 does take some time. Calculating how many hosts could fit in there and what the address-range is, is an even bigger challange.

Luckily there exists a nice tool called the subnet calculator, which does all of these calculations in an instant. The Internet offers lots of these; some are Win32 applications while others run online; Some require to input each octet individually, others are more liberal.

After some hours of search, I didn’t find a subnetcalc that fits my needs. I’m sure it exists somewhere in the 427000 hits, I just didn’t find it. Instead, I wrote my own one.

Continue reading ‘Subnet calculator’ »