Category Archives: Tips

Duply credential error when using Amazon S3

Duply is a convenient wrapper around duplicity, a tool for encrypted incremental backups I’ve used for the last couple of years. Recently, after a recent upgrade, my Amazon S3 backups failed, reporting the following error:

    'Check your credentials' % (len(names), str(names)))
NoAuthHandlerFound: No handler was ready to authenticate. 1 handlers were checked. ['HmacAuthV1Handler'] Check your credentials

Boto, the backend duplicity relies on for the Amazon S3 backend, requires to pass authentication parameters through the AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY environment variables. As different backends require different variables, duply used to make that transparent, one would just set TARGET_USER and TARGET_PASS and duply would take care of the rest. However, duply 1.10 broke compatibility and requires you to set the variables yourself. Hence, the fix is to replace the TARGET_* variables with exported AWS_* variables:

# TARGET_USER='XXXXXXXXXXXX'
# TARGET_PASS='XXXXXXXXXXXX'
export AWS_ACCESS_KEY_ID='XXXXXXXXXXXX'
export AWS_SECRET_ACCESS_KEY='XXXXXXXXXXXX'

Calculate Google Drive Folder Size Using `rclone`

Google Drive lacks a very basic feature: calculating folder size. There is no solution in the web interface to view the total size of a given directory. There are a couple of dubious looking online “folder size analyzers” request access permissions to your Google Drive and offer you the basic functionality of calculating folder size. While those apps, have a legitimate need for access permission to your account, you may consider given those permissions to random apps a questionable decision.

The (very) useful tool rclone, which provides rsync like interface to many cloud storage providers, implements this functionality. After configuring rclone to work with your Google Drive, use the size command to determine the size of a given folder:

$ rclone size "gdrive:Pictures/"
Total objects: 1421
Total size: 9.780 GBytes (10501374440 Bytes)

The size is calculated recursively. However, there is no simple way to display the size of each sub-directory recursively.

`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).