Category: Tech

The geek is strong is this one

Categories
General Tech

Jason’s Alternator Story

My friend Jason Rule was in Edmonton for the Father’s Day weekend and had a funny trip back from Edmonton to Calgary. In his own words, here is what happened.

[Alternator photo by goodharbor. Used with permission.]

While driving in Edmonton, I noticed at one point my alternator light go on… It just happened for a second and I did not really think anything of it. Later as I was leaving the city, the light was about 50% on, so basically it’s putting out some power—the exact amount the car needs. By the Edmonton International Airport, the light was on and I was running on battery power (the battery power was making the spark for the engine).

I went into conservation mode and turned off all electrical systems but the radio.

Around Red Deer, the engine started skipping a beat and the radio died. There was not enough power to spark the plugs… I pulled over (leaving the engine running) and quickly wired up my second battery to the engine by the wires I had pre-installed years before. The car’s back to life!!! I turn off the radio and keep driving.

It starts raining… I try using the windshield wipers, but there is so little power, they take about 10 seconds to cycle. So, with no fan (defog) and no wipers… I continue.

I need to stop in Didsbury where Brooke’s dad lives. I needed to pick something up and get as much power as possible. About 10 km from Didsbury, the dash fails, no speedo, nothing… About 3 km from Didsbury, the car is skipping again. I am approaching a stop sign and go to apply the brake. The power going to the brake lights makes the engine quit. As I was still travelling fast, I pop the clutch and get the engine running again. I then stop the car with engine breaking and the ebrake. I just get to the house and park in front of her dad’s truck.

Without explaining what I was doing, I start his truck and start transferring as much power as possible via booster cables into the car battery. I also start charging the second battery via a charger…. How long to wait… it’s 8 p.m. and the sun is going down. By 9:45 p.m., it will be dark and I will need headlights and I will be screwed… But, I need as much power as possible.

I pull out almost all of the circuit breakers from the fuse box. At 8:15 p.m., I start driving, extra battery not connected, car battery driving the engine. There are no electrical systems at all…

I make it to just north of Airdrie. Engine, with no warning, fails… Poor steering and brakes (that was a surprise). I pull over and remove the primary battery and install the secondary battery. I tried to start the engine, but there is not enough power to turn the starter…. I get out of the car, push it backwards, down the little hill I was on… Pop the clutch and the engine is running… I’m off.

I make it to Deerfoot and McKnight. Engine again quits… I pull over and call Brooke. The Deerfoot Trail is nuts as cars are going by at nuts speeds. She comes quickly and now it’s about 9:30 p.m. I pull the extra battery from her truck and throw it into the car. The car starts and we start driving—Brooke following me and being my lights.

About five blocks from home, car again fails… We load the gear into the truck and leave the car there for the night… We come back the next morning with a charged battery and drive home.

Two points to this story:

  1. All that crap I carry in my car sometimes comes in very handy.
  2. MacGyver himself would have been proud!

— Jason

Categories
Linux

My First Bug Report

I recently submitted my first bug report to the Debian Project, regarding mod_dav and apache2. It was accepted by the maintainers of the relevant packages, and they’re taking the necessary steps to fix it.

So I’m proud of my little contribution. 🙂 Yay for me! Yay for Debian!

Categories
Linux Python Sysadmin

An awesome blog about Python, Linux, and System Administration

I recently discovered an awesome blog about Python, Linux, and System Administration. Chris Siebenmann is a sysadmin for the University of Toronto Unix Systems Group. I could spend hours reading his archives. Smart guy. Articles are short and informative to the max. Hope you enjoy it:

Categories
Sysadmin

Emailing cron output to different users

When a cron job generates output on either stdout or stderr, the output gets mailed to the owner of the crontab. Now, you can specify an alternative email address by setting the MAILTO environment variable in the crontab, but this applies to all jobs in the crontab.

So, if you want the output of different jobs to get mailed to different users, then you can just redirect the stdout and stderr of each job to the mail command like this:

13 02 * * *     /bin/backup 2>&1 | /usr/bin/mail -s "Cron <root@exobox> /bin/backup" \
user@example.net
Categories
Linux Sysadmin

MTR as a combined traceroute and ping tool

“mtr combines the functionality of the traceroute and ping programs in a single network diagnostic tool.” And it’s really cool.

Like ping, it sends “echo” packets from your machine to the target machine to measure latency and packet loss along the network path, but it continuously displays updated statistics in real time as it operates.

Like traceroute, it shows the names or IP addresses of each machine along the network path, also updating these statistics for each machine.

Here’s some (frozen) sample output from the ncurses mode (terminal mode) mtr:

                                My traceroute  [v0.71]
exobox (0.0.0.0)                                             Thu Dec 21 16:15:01 2006
Keys:  Help   Display mode   Restart statistics   Order of fields   quit
                                             Packets               Pings
 Host                                      Loss%   Snt   Last   Avg  Best  Wrst StDev
 1.                                         0.0%    20    0.4   0.3   0.2   0.7   0.1
 2.                                         0.0%    20    1.6   1.4   1.0   2.7   0.4
 3.                                         0.0%    19    1.3   1.3   1.0   2.7   0.4
 4. 10.0.0.25                               0.0%    19    1.1   1.2   1.0   2.7   0.4
 5. 219.142.10.17                           0.0%    19    1.4   2.6   1.2  16.0   3.3
 6. bj141-130-121.bjtelecom.net             0.0%    19    1.4   1.6   1.4   2.5   0.3
 7. 202.97.57.221                           0.0%    19  199.3  12.0   1.3 199.3  45.4
 8. 202.97.37.9                             0.0%    19    1.7  35.7   1.3 186.5  56.2
 9. 202.97.53.146                           0.0%    19    1.8   2.0   1.5   4.8   0.8
10. 202.97.61.50                            0.0%    19  284.6 292.2 278.3 305.8   8.7
11. so-4-0-0.mpr2.lax9.us.above.net        15.8%    19  286.2 291.9 278.6 325.2  11.5
12. so-5-0-0.mpr1.iah1.us.above.net        15.8%    19  313.2 323.8 311.3 340.5   8.6
13. so-5-3-0.cr1.dfw2.us.above.net          5.3%    19  319.6 331.1 314.1 404.6  20.3
14. so-0-0-0.cr2.dfw2.us.above.net         11.1%    19  696.0 718.7 693.3 797.2  33.7
15. so-3-1-0.cr2.dca2.us.above.net         36.8%    19  347.4 354.9 342.5 368.7   8.6
16. so-0-1-0.mpr1.lhr3.uk.above.net        11.1%    19  421.5 423.6 411.1 438.2   7.8
17. so-1-0-0.mpr3.ams1.nl.above.net        11.1%    19  433.9 438.9 422.4 514.1  22.0
18. DutchDSL.above.net                     33.3%    19  423.1 432.7 418.7 463.0  11.4
19. ge-0-1-0-v189.rtr1.ams-rb.io.nl        27.8%    19  405.8 414.7 398.2 434.6  11.6
20. 213.196.40.242                         23.5%    18  404.8 418.1 399.9 485.8  21.9

Looking at the Avg column (units in ms), the above output shows that my network packets pass through Beijing Telecom’s routers to the U.S., then to the U.K., and finally to their destination in the Netherlands. A large latency increase occurs between lines 9 and 10 (presumably leaving P.R. China), and another between lines 13 and 16 (U.S. to U.K.).

mtr has some interesting display modes besides the above, where it shows the latency of each packet graphically according to a dynamic scale. In this way, the above points of really large latency can be easily detected.

mtr can be obtained from the mtr website, or it can be installed in Debian/Ubuntu by:

# apt-get install mtr-tiny

or

# apt-get install mtr

for the ncurses or X11 versions, respectively, although mtr-tiny appears to be installed by default in the Debian and Ubuntu machines I have tested. So you may already have it.

Categories
Sysadmin

The Machines Have Taken Over

The latest comic from Dilbert speaks some truth about life as a Sysadmin:

[Dilbert: The machines have taken over]

Categories
Linux

Ubuntu Open Week Begins Tonight

If you’re curious or interested in getting involved in the Ubuntu community, “Ubuntu Open Week” begins tonight. It’s “a week of IRC tutorials and sessions designed to encourage more and more people to join our diverse community”. More information is here:

https://wiki.ubuntu.com/UbuntuOpenWeek

The times in the calendar are UTC, so just add 8 hours for China. For example, the first session on Monday on the “Ubuntu Desktop Team – Sebastien Bacher” at 15:00 UTC will actually occur at 23:00 tonight, Beijing time. Of notable interest is the “Ask Mark” session on Tuesday, featuring Ubuntu founder Mark Shuttleworth.

By the way, I plan on attending some of the earlier-in-the-evening sessions, but once it gets too late I’ll just let my IRC client log the rest of them while I’m sleeping. 😉

Categories
Tech

Matrix Transform

The latest comic from xkcd is just too funny. Check it out:

[Matrix Transform by xkcd.com]

Categories
Sysadmin

How to send an entire domain to /dev/null in Postfix

At Exoweb, our software developers use bogus email addresses of the form *@example.com (where I mean “example.com” literally, not as an example) to test their software’s ability to send email. Since I don’t want our Postfix server to attempt to deliver these messages out on the Internet, I need Postfix to handle these messages and blackhole them (make them disappear, sent to /dev/null). So what follows are instructions on how to blackhole an entire domain in Postfix.

First, we add a virtual_alias_maps entry to /etc/postfix/main.cf so that we can specify example.com as one of our virtual domains:

virtual_alias_maps = hash:/etc/postfix/virtual_alias

Inside /etc/postfix/virtual_alias, add a catchall address:

@example.com      blackhole@localhost

We have to use blackhole@localhost here and not /dev/null/ because virtual_alias_maps cannot run commands—it can only forward to real addresses. So we put an entry inside /etc/aliases to handle the blackhole:

blackhole:      /dev/null

This assumes that one of your mydestination domains in main.cf is localhost so that Postfix will actually consult the aliases file.

In order to make these changes take affect, you have to rebuild the aliases database, build the virtual_alias database, and reload your Postfix configuration. Respectively:

# newaliases
# postmap /etc/postfix/virtual_alias
# postfix reload

Now, any emails you send to blackhole@localhost will disappear, and so will any emails addressed to anyone@example.com (provided they are relayed through your Postfix server).

Footnote: The top-level and second-level domain names that are reserved for testing can be found in RFC 2606.

Categories
Linux Palm Tech

How to convert CHM files under Linux

CHM files, known as Microsoft Compressed HTML Help files, are a common format for eBooks and online documentation. They are basically a collection of HTML files stored in a compressed archive with the added benefit of an index.

Under Linux, you can view a CHM file with the xchm viewer. But sometimes that’s not enough. Suppose you want to edit, republish, or convert the CHM file into another format such as the Plucker eBook format for viewing on your Palm. To do so, you first need to extract the original HTML files from the CHM archive.

This can be done with the CHMLIB (CHM library) and its included helper application extract_chmLib.

In Debian or Ubuntu:

$ sudo apt-get install libchm-bin
$ extract_chmLib book.chm outdir

where book.chm is the path to your CHM file and outdir is a new directory that will be created to contain the HTML extracted from the CHM file.

In other Linuxes, you can install it from source. First download the libchm source archive from the above website. I couldn’t get the extract_chmLib utility to compile under the latest version 0.38, so I used version 0.35 instead.

$ tar xzf chmlib-0.35.tgz
$ cd chmlib-0.35/
$ ./configure
$ make
$ make install
$ make examples

After doing the “make examples“, you will have an executable extract_chmLib in your current directory. Here is an example of running the command with no arguments and the output it produces:

$ ./extract_chmLib
usage: ./extract_chmLib <chmfile> <outdir>

After running the utility to extract the HTML files from your CHM file, the extracted files will appear in <outdir>. There won’t be an “index.html” file, unfortunately. So you’ll have to inspect the filenames and/or their contents to find the appropriate main page or Table of Contents.

Now the HTML is yours to enjoy!

Resources

I got help in writing this article from here and here.