Developing Tiny Core Linux extensions

Packaging AppImages

The method shown for packaging AdoptOpenJDK can be adapted for AppImage files. The only difference is that you won't be able to unpackage them with tar, since their contents are encapsulated as filesystem images instead. AppImage files can be extracted using the --appimage-extract switch. For example, in order to extract Nextcloud-Client after downloading it, run:

$ chmod +x Nextcloud-2.6.4-x86_64.AppImage
$ ./Nextcloud-2.6.4-x86_64.AppImage --appimage-extract

Remember: In an AMD64 system, you will need to ensure that /lib64/ld-linux-x86-64.so.2, the dynamic linker, is available. Otherwise, AppImages won't work. The best way to do this is to create /lib64 if it does not exist and then make a symlink from /lib/ld-linux-x86-64.so.2 to /lib64/ld-linux-x86-64.so.2.

Packaging from Source Code

The procedure for packaging a piece of software from its source code is not complex. Instead of taking a precompiled build and decompressing it into the extension file tree, you just compile the software directly into the extension file tree:

$ cd source_code
$ ./configure --prefix=/usr/local
$ make
$ sudo make install \
DESTDIR=/tmp/package-extension

The --prefix switch is required to configure the software to operate under /usr/local once installed. The make install command is passed a DESTDIR parameter to get the software installed directly into the extension folder (rather than the actual operating system doing the building!).

Making Your Extension Official

If you don't intend to share your extensions, you are done. However, if you intend to submit your extension to an official repository, you still have work to do.

Every submission to the official repository needs a file that contains the extension's checksum, a list of the files contained in the extension, a generic information file, and a list of dependencies.

To generate the extension's checksum, use the following commands:

$ cd /tmp
$ md5sum adoptopenjdk-12.tcz >> adoptopenjdk-12.tcz.md5.txt

Then, you can generate a valid list of the extension's contents with the following commands:

$ cd /tmp/package-adoptopenjdk-12
$ find * \! -type d >> /tmp/adoptopenjdk-12.tcz.list
$ sort -o /tmp/adoptopenjdk-12.tcz.list /tmp/adoptopenjdk-12.tcz.list

In order to generate a valid information file, you should download an existing file from the official repository and use it as a template [6].

For the list of dependencies, check the documentation of the software you are packaging. You can also use ldd to obtain a list of the libraries a binary uses, which is a great starting point if the documentation is unhelpful:

$ find * -type f | xargs file | grep ELF |cut -f 1 -d \: | xargs ldd

You should place the list of dependencies in a file with the extension *.tcz.dep (e.g., adoptopenjdk-12.tcz.dep). Check the official repository for examples.

In order to ensure your dependency list is correct, boot a Tiny Core Linux instance with the base and norestore cheat codes. Then install the dependencies listed in the *.tcz.dep file using tce-load. Try to load and use your new extension. If everything works, your list of dependencies is correct.

The official policy for extensions is that they should not touch anything in the filesystem structure's higher levels directly. An extension's files should be placed in /usr/local. If you need the extension to make any modification elsewhere in the filesystem, you should use a tce.installed script, as shown in this article.

You will also need to strip binaries within the extension. This is easily accomplished with the strip command:

$ find * -type f | xargs file | grep ELF |cut -f 1 -d \: | xargs sudo strip

In order to find out if extensions are fully compliant, Tiny Core Linux offers a submitqc extension. Using this extension is as easy as placing the extension, the *.info file, the *.dep file, and the *.md5.txt file in the same folder. Then open a terminal in the folder and run:

$ submitqtc --libs

The program will generate a log and report any issues it encounters.

If you are packaging graphical applications, it may be a good idea to generate a freedesktop-compliant entry, such as the one shown in Figure 3. This will allow your extension to appear in the desktop environments' menus and in the Tiny Core Linux's default Wbar (Figure 4).

Figure 3: Placing weasis.desktop in /usr/local/share/applications makes the extension available in the desktop environment's menus.
Figure 4: My custom Weasis extension (a medical image viewer) shows up in the Wbar.

Finally, remember to include the software license! The software that governs the distribution and use of your extension should be installed in /usr/local/share/doc/$extension (where $extension is the name of your extension).

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