Tanguy Ortolo - Debian

Suspend your computer from a non-mainstream desktop environment

Tanguy — Tue, 05 Mar 2013 12:05:00 +0100

UPower for regular users

Major desktop environments usually provide a user-friendly menu to suspend your computer. Internally, if seems to use something called UPower, which uses something called PolicyKit, which in turn may or may not use another piece called ConsoleKit (do not ask me what all these pieces are and how they relate to each other, I do not know and I do not want to know). For the regular user, the result is the following: when they click on that button, it suspends their computer.

UPower for command line users

However, if you are using a more unusual desktop environment, for instance a simple, light window manager, you will not have such a button. And no, UPower does not provide a simple command line tool to suspend your computer¹ (they probably consider that command line is out of fashion…). Well, in case you need it, here is a way to suspend your computer from a command line or whatever: just alias it or bind it to a key shortcut. It uses some dark DBus magic:

$ dbus-send --system --print-reply --dest='org.freedesktop.UPower' \
    /org/freedesktop/UPower org.freedesktop.UPower.Suspend

If you prefer to hibernate your computer, that is, to suspend it, not to RAM but to disk:

$ dbus-send --system --print-reply --dest='org.freedesktop.UPower' \
    /org/freedesktop/UPower org.freedesktop.UPower.Hibernate

As you can see, for some reason it requires some duplication of information: the name “org.freedesktop.UPower” appears three times in that command line: in the “destination”, “object path” and “interface member”, whatever that could mean. Again, do not ask me why, I know nothing about that and I do not want to.

Notes

Actually, UPower does provide a command line tool called upower, but the only thing it does (monitoring power sources) is not really useful for that matter. ↑

One archiver to rule them all: bsdtar

Tanguy — Thu, 21 Feb 2013 12:21:00 +0100

Sometimes, you have to use ZIP archives, or worse, RAR archives (curse them!), with one significant annoyance: zip, unzip, rar and unrar use a rather uncommon command line convention, compared to the usual tar, cpio and pax.

This is where bsdtar and bsdcpio come handy: these two equivalent tools from FreeBSD do not directly implement any archive format, relying on libarchive to do that instead. That allows you to do thinks like:

% bsdtar -tf crap.rar
% bsdtar -xf crap.rar
% bsdtar --format zip -cf stuff.zip stuff

Too bad it does not have a -a option to automatically select the archive format as GNU tar does.

.diff or .patch?

Tanguy — Fri, 15 Feb 2013 19:35:00 +0100

Silly question: when you use diff(1) to produce a file to be applied with patch(1), do you call the result a diff or a patch? Do you name it foo.diff or foo.patch?

Using the UDF as a successor of FAT for USB sticks

Tanguy — Wed, 30 Jan 2013 13:09:00 +0100

FAT

USB sticks are traditionally formatted with FAT 32, because this file system is implemented by almost every operating system and device. Unfortunately, it sucks, as it cannot use more than 2 TiB, store files larger than 2 GiB or store symbolic links for instance. In a word, it is an obsolete and deficient file system.

exFAT

Good news: someone addressed that problem. Bad new: that someone is Microsoft. So as you could expect, exFAT, the extended FAT, is a stinking proprietary, secret and patented file system. There are free implementations of that shit, but it is safer to stay away from it.

UDF to the rescue!

Good news: there is one file system that is implemented almost everywhere as well, and which does not suffer from such limitations. UDF, the Universal Disk Format, is an ISO standard originally designed for DVDs, but it is perfectly usable for USB sticks. It also supports POSIX permissions, with one killer feature for removable media: a file can belong to no specific person or group.

So, to use it, assuming you USB stick is /dev/sdc:

$ dd if=/dev/zero of=/dev/sdc bs=1M count=1
$ mkudffs -b 512 --media-type=hd /dev/sdc

The initial dd is to erase the existing partition table or file system information, to prevent you USB stick from being detected as a FAT after it has been formatted with UDF.

The -b 512 is to force a file system block size equal to the USB stick's physical block size, as required by the UDF specification. Adapt it if you have the luck of having a USB stick with an more appropriate block size.

After that, you USB stick will be usable for reading and writing with GNU/Linux and the other free operating systems of course, but also with current versions of Windows (read-only with the outdated version XP) and with MacOS.

Do not reCAPTCHA!

Tanguy — Fri, 25 Jan 2013 20:26:00 +0100

You probably know reCAPTCHA already: for the webmasters and the end user, it is an antispam system which asks you to read distorted words in order to prove that you are a human and not a spamming bot. This service has another end: instead of generating its distorted texts, it takes them from printed books to help digitalizing them.

The problem

In theory, this is an excellent idea, which should help preserving and distributing parts of the human culture. And, in the beginning, it was used in such a way, with reCAPTCHA participating in the Gutenberg project which digitalizes books from the public domain to offer them freely (as in free speech) to everyone. In 2009 however, reCAPTCHA was bought by Google. Now they do not participate in the Gutenberg project any more, instead they are digitalizing stuff from the New York Times and from Google Books. They do not provide much detail about that, but it does not seem that they distribute them in a free way afterwards¹.

To put it boldly: they use people's brain power to digitalize books for their own exploitation monopoly, which is wrong. These books should be made available under a free license.

Suggestion

Do not help reCAPTCHA. If you are a webmaster, try to use another more ethical system. If you are an end user, and you are facing a reCAPTCHA test, avoid putting the exact answer but try inserting small mistakes (not big ones, which get detected and make you fail the test). And ask Google to free the books they digitalized using your brain.

Notes

I may be wrong but I learnt to be suspicious in the context of digital culture. Please Google, if you do publish your books digitalized with reCAPTCHA under a free license, tell me, or rather, tell it to everyone and display it proudly in the reCAPTCHA website. ↑

The drawback with tiling window managers…

Tanguy — Tue, 22 Jan 2013 13:47:00 +0100

… is that you cannot use funny desktop programs such as Xsnow or XPenguins. :-(

That is, you can run them, of course, but since you almost never see your desktop because it is by design entirely covered with windows, they are just useless, which is too bad because they rock otherwise.

rlwrap: give readline super powers to any command line tool

Tanguy — Sat, 05 Jan 2013 17:15:00 +0100

Did you ever use a tool such as netcat, which has no history and does not allow you to edit the line you are typing?

% nc localhost smtp
220 cocorico.example.com ESMTP Postfix
HELO localhost
250 cocorico.example.com
MAIL FROM: <tanguy@localhost>
250 2.1.0 Ok
RCTP TO: <tanguy@localhost>
502 5.5.2 Error: command not recognized
^[[A Sh*t, line recall does not work!
502 5.5.2 Error: command not recognized

Here comes rlwrap: it is a small and useful tool that wraps any command line-oriented tool using readline to provide you a history allow you to edit each line before you send it:

% rlwrap nc localhost smtp
220 cocorico.example.com ESMTP Postfix
HELO localhost
250 cocorico.example.com
MAIL FROM: <tanguy@localhost>
250 2.1.0 Ok
RCTP TO: <tanguy@localhost>
502 5.5.2 Error: command not recognized
↑ RCTP TO: <tanguy@localhost> ⇱…

rlwrap's effect is hard to describe with a transcript, so here are two screencasts, with and without it. If you often use tools such as netcat, try it!

Sorry your browser does not support videos, you may want to try another one.

SMTP session without rlwrap

Sorry your browser does not support videos, you may want to try another one.

SMTP session with rlwrap

A desktop file managers failure: writing an USB stick image

Tanguy — Sun, 30 Dec 2012 23:49:00 +0100

Installing an operating system

When you want to install a new operating system, the first thing to do is to get an installer medium, which usually involves two steps: downloading an image, and writing it to a medium. There are two major types of media usable for that purpose: optical discs and USB sticks. There used to be a third one, floppy disks, but it is no longer used, and it was conceptually very similar to USB sticks.

Power-user

If you are a power-user, you probably use USB stick, to be able to reuse them and because they are easier to carry. For you, writing an optical disc or an USB drive is almost the same:

$ wodim image.iso
$ dd if=image.img of=/dev/sdc

Regular user

But what would you suggest to a normal user? USB stick? You should not: while it is technically much easier to write an USB stick (just copy blocks from the image to the peripheral file, without any need to use any specific function), desktop file manager make it much harder. Indeed, for a desktop user, burning an ISO image to an optical disk is quite simple: right-click on the image file and choose the “burn” option. But writing an image to an USB stick? There is no similar option, so that will involve calling a power-user friend, which will tell you to open a terminal and type “dd if=…”.

Nautilus's context menu: write to optical disc…

Moral

Power-users: Continue using USB sticks as installation media, but tell regular users to use optical discs until desktop file managers adapt.
Regular users: Use optical discs. If your computer does not have an optical reader, either invite a power user friend, or buy an USB optical reader.
Desktop developers: Please, fix that! Writing an image to an USB stick should not be harder than burning it to an optical disc! People are using more and more computers without an optical reader, and that situation is certainly not new, as it is only similar to that of the time when we were using floppy disks.