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
Philosophy

61-Point Relaxation

The following relaxation exercise comes from Stephen LaBerge and Howard Rheingold’s Exploring the World of Lucid Dreaming (1990), which they adapted from Swami Rama’s Exercise Without Movement (1984). It’s one of my favourite meditations—one that I can do in bed, waiting in line at the bank, or while riding in a taxi. Anywhere I can be still, really. I need more practice, though, because I rarely succeed in ending on the number 61. I’m often off by one or two.

I believe I like this meditation because it is methodical, with clearly laid out steps to take. Plus each step gives me feedback that feels good, and also serves to tell me when to move on to the next step. Aside from keeping track of the number I’m on, I rarely get lost.

Please try it. You’ll need to experience it for yourself to see if this method suits you.

1. Study the figure

The figure below illustrates 61 points on the body. To do this exercise, you need to memorize the sequence of points. (This is not difficult, because the points are arranged in a simple pattern.) They begin at the forehead, travel down and up your right arm, then across to your left arm, down your torso, down and up your right and left legs, then back up your torso to the forehead.

[61-point relaxation diagram]

2. Focus your attention on one point at a time

Begin at your forehead. Focus your attention between your eyebrows and think of the number one. Keep your attention fixed at Point 1 for several seconds until you feel that your awareness of the location is clear and distinct. Think of your self being located at this point. Before moving on to the next point, you should feel a sense of warmth and heaviness at this spot.

3. Move through each point in sequence

In the same manner, successively focus your attention on each of the first thirty-one points. Proceed slowly, and imagine your self being located at each point as you reach it. Feel the sense of warmth and heaviness before moving on. Do not allow your mind to wander. At first you may find this difficult to do; you will discover that at times you suddenly will forget that you are doing the exercise and start daydreaming or thinking about something else. If you lose your place, return to the beginning or the last numbered point you attended to, and continue. Practice with thirty-one points until you can attend to them all in sequence without daydreaming or losing track.

4. Extend your practice to include all sixty-one points

When you can attend to thirty-one points in sequence, repeat Steps 1 and 2 with all sixty-one points. Practice this until you can do all points without losing your focus. Now you are ready to use this exercise with lucid dream induction techniques.

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.

Categories
General

Mirror

It’s pretty amazing what you find when you search for “mirror” in Google Images and Flickr. This is a collection of what I just found.


[Mirror collection]

Categories
Sysadmin

Spaghetti Wiring

When you work in a software development shop, spaghetti code is most certainly frowned upon. What about spaghetti wiring?

[Spaghetti wiring]

So this was the remains of the small electrical fire that occurred 15 minutes before I arrived at the office today… the charged main circuit to the room that houses most of our developers, their computers, and the all-important Ice Box.

Do you think this is enough to convince the building management that the building’s wiring needs professional help? No, unfortunately, I think we’ll still have to fight them to get adequate electrical capacity and safety. 🙁

Categories
China

I Love Chocolate Too!

This piece of writing that came across my desk made me laugh really hard today:

Cities are the centers of ecomoy developement, the centers of power, water and fossile fuel consumption and the centers of pollutant producing. The atmospheric pollution in cities is maily from vehicle dispersion, industrial consuming, energy producing and resident-consuming chocalate.

I think the author means charcoal, as in residential heating. 😉