Category Archives: Tips

`rsync` and FAT File-Systems

I’m using rsync to sync files from my computer to a FAT formatted SD card. Using the --update flag to rsync makes it “skip files that are newer on the receiver”. It seems that it should work as follows: After the first sync, any subsequent syncs will only transfer those files which changed in the meantime. However, I noticed that transfer times are usually longer than expected, which led me to think that things are not working as they should.

As --update relies only on modification date, obviously something is wrong with it. After ruling out several other possibilities, I’ve guessed that the modification date of some files get mangled. A quick check about FAT revealed that FAT can only save modification times in 2 second granularity. I’ve also used rsync’s --archive flag, which among other things attempts to preserve modifications times of the files it copies. But what about FAT’s lower granularity for modification time? That was apparently the culprit. Some files when copied got a modification time which was up to 1 second before the original modification time! Hence, every time I’ve synced, from rsync’s perspective, the target was older than the source, and hence needs to be overwritten.

This can be demonstrated by the following session:
Continue reading

LyX: Missing title when passing `ignorenonframetext` to Beamer

Passing ignorenonframetext as an option to Beamer, causes it to ignore all the text that is not inside a frame. It is useful when you want to add content for the article version of the presentation (or simply script lines for yourself) that would not show in the regular presentation. LyX puts the title elements outside any frame. Therefore, if you use ignorenonframetext you end up missing the title frame. The solution is to manually wrap the title block (the title, author, institute, etc.) in a frame and append to it \maketitle. This will cause the title frame to be rendered correctly.

KOMA-Script: Specifying Binding Correction for RTL Documents

The KOMA-Script bundle provides an option to specify the amount of binding correction needed in order to compensate for the width lost in the binding process. By default, it is added to the left margin, which is where the binding is applied for Left to Right languages. However, if a document is written in Hebrew or Arabic, one binds it on the right. The KOMA-Script manual does not consider that option. After a bit of playing I’ve found out that simply using a negative value for the binding correction works.

For example, if in an English document you would use

\documentclass[BCOR=8.25mm]{scrreprt}

For Hebrew you would set

\documentclass[BCOR=-8.25mm]{scrreprt}

Playing Opus Files on Android Marshmallow (6.0)

The Opus codec provides superior audio quality over codecs such as AAC, MP3 and Vorbis. Android has support for Opus since Android 5.0 (Lollipop). However, when I tried playing Opus files on My LG G4, it wouldn’t recognize the file as a media file at all. It turns out, that the default .opus extension is not recognized by Android. The workaround is to change the extension to .ogg. Generally speaking, this is technically correct, as most Opus streams are encapsulated by an Ogg container, however, .opus is the recommended extension (but apparently not for Android).

Fixing HTML Rendering in Wine on Debian Jessie

Some application rely on Internet Explorer to provide HTML rendering capabilities. Wine implements the same functionality based on a custom version of Mozilla’s Gecko rendering engine (the same engine used in Firefox). In Debian Jessie you have a package called libwine-gecko-2.24 (the version is part of the name) which provides this rendering engine for Wine. However, different versions of Wine require different versions of wine-gecko. The package provided in Debian Jessie, matches the Wine version provided by wine-development from the main Jessie repository (1.7.29). Unfortunately wine-development from the jessie-backports if of version 1.9.8 and requires wine-gecko of version 2.44 which is not provided by any Debian repository. This will lead to errors like

Could not load wine-gecko. HTML rendering will be disabled.

and blank spaces where HTML content would be rendered in many applications.

The solution would be to manually install the required version of wine-gecko. We start by downloading the MSI binaries provided by Wine

$ wget https://dl.winehq.org/wine/wine-gecko/2.44/wine_gecko-2.44-x86.msi
$ wget https://dl.winehq.org/wine/wine-gecko/2.44/wine_gecko-2.44-x86_64.msi

Now install the required one, based on whether you are using 32bit or 64bit wine environment:

wine-development msiexec /i wine_gecko-2.44-x86.msi

(be sure the setup the correct $WINEPREFIX if needed).

en_IL: English locale for Israel

Update: The new locale was committed to glibc and should be part of glibc-2.24.

Most Israelis are literate in English, and for a large percentage of them, English is also the preferred language when it comes to computers. They prefer English, as it solves right-to-left issues and general inconsistencies (it might be annoying when some programs are translated ands some not). The downside is, that currently, the existing English locales are not suitable for Israel, as there are cultural differences:

  • American English spelling is more common in Israel.
  • The metric system is used, along with the relevant paper sizes (“A4” instead of Letter).
  • Dates are written in dd/mm/YYYY format, unlike in the USA.
  • The first day of week, and also the first workday is Sunday.
  • The currency used is ILS (₪).

So, up until now users had to choose locales such as en_US or en_GB and compromise on some stuff. To solve this issue, and create a truly suitable English locale for Israel, I wrote a localedef file for the en_IL locale.

To install the new locale, copy the en_IL file from the gist below and place under /usr/share/i18n/locales/en_IL (no extension). Next

# echo "en_IL.UTF-8 UTF-8" >> /usr/local/share/i18n/SUPPORTED

Now, complete the installation by running dpkg-reconfigure locales and enable en_IL.UTF-8 from the list, and set it as the default locale.

nginx and SNI

Server name indication (SNI) allows you serve multiple sites with different TLS/SSL certificates using a single IP address. Nginx has support for SNI for quite some time and actually setting it up is easy, simply add server entries for the corresponding sites. There is one caveat, the server_name entry must come before the server_certificate in order for SNI to be activated:

server {
    listen          443 ssl;
    server_name     www.example.com;
    ssl_certificate www.example.com.crt;
    ...
}

server {
    listen          443 ssl;
    server_name     www.example.org;
    ssl_certificate www.example.org.crt;
    ...
}

is good, but

server {
    listen          443 ssl;
    ssl_certificate www.example.com.crt;
    server_name     www.example.com;
    ...
}

server {
    listen          443 ssl;
    ssl_certificate www.example.org.crt;
    server_name     www.example.org;
    ...
}

will serve the wrong certificate for www.example.org.

WordPress.com Login Loop

Sometimes, when I try to use certain functions on wordpress.com, I get redirected to a login page. After I sign-in, I get redirect again to the same login page. This repeats in an endless loop. It usually doesn’t bother me, as I self-host my blog, but for some things, like the yearly annual report that came in about two weeks ago, it does bother. I looked up into the matter, and the issue turned up to be due to blocking third-party cookies. To resolve the endless login loop, you need to add https://wordpress.com (note the https) to the exception list of accepted third-party cookies (In Firefox it’s under Preferences -> Privacy -> Exceptions).

Skip Updates When Using the Let’s Encrypt `letsencrypt-auto` Client

To use Let’s Encrypt CA to issue free certificates, you need to use their client. The recommended method to install it is to use letsencrypt-auto, a script that automatically fetches and installs all the required dependencies. There is no doubt, that the letsencrypt-auto is the fastest and simplest way to get a Let’s Encrypted client up and running. I’ve used it myself, when I wrote a guide to get Let’s Encrypt up and running easily.

Automatically updating required dependencies, has its downside. As letsencrypt-auto does it every time you run it, it quickly gets annoying. Running a simple ./letsencrypt-auto --help takes a whopping 15 seconds, just figuring out that there are no updates available. Supposing that you know that no update are available, and you wish to save some time, you can run the letsencrypt executable directly, skipping the updating process of lestencrypt-auto:

~/.local/share/letsencrypt/bin/letsencrypt

Most of the actions require you to be root, so you might need to run it with sudo.

You can expect this issue to be resolved in the future. There is already an open issue for it and an active work that will resolve it.

Installing Debian Unstable’s source Packages in Debian Jessie

Sometimes a package that you need is not available for Debian Jessie, but you can find it for Sid (unstable). You may be tempted to try to install it manually, by downloading the binary deb package, but it will most likely fail due to binary incompatibilities with different libraries’ versions you have. The better method will be to get the source package used to build the binary package, and build it yourself. Most of the time the process is not as hard as it sounds.

First, a short preliminary setup is needed Add the following lines to /etc/apt/sources.list:

deb http://http.debian.net/debian jessie-backports main
deb-src http://httpredir.debian.org/debian unstable main contrib

You can replace unstable with testing if you prefer to use packages from testing. Update the lists of packages

sudo apt-get update

Next you need, to get the build dependencies for your package. The example below uses the package lyx:

sudo apt-get build-dep lyx/unstable

Now you are ready to fetch and build the source package:

sudo apt-get source -b lyx/unstable

Finally, you will see in the current directory the resulting DEBs. Simply install them:

sudo gdebi lyx-common_2.1.4-2_all.deb
sudo gdebi lyx_2.1.4-2_amd64.deb

You can later mark the dependecies that you manually installed as automatic:

sudo apt-mark auto lyx-common