A library for making self-extracting tar files.

This was created specifically for the s6-overlay project. It is not currently recommended for creating generic, self-extracting tar files - it has behavior that is specific to the s6-overlay project, is only tested with GNU tar, and only tested with the s6-overlay tar file.

The library is compiled as a static archive with a main function already defined. The main function will extract the contents of a tar file, it expects for three symbols to exist:

• unsigned char _binary_payload_tar_start[]
• unsigned char _binary_payload_tar_end[]
• size_t _binary_payload_tar_size

main will extract the payload to a given destination.

It will only create directories on the filesystem if they do not exist. This is primarily to support distributions that have replaced /bin with a symlink to /usr/bin. Most tar implementations will remove /bin and replace it with a directory (assuming /bin is a directory inside the tarfile).

To produce the payload object you can use ld:

ld -r -b binary payload.tar -o payload.o 

Then link everything together into an executable:

gcc -static -o installer libjustc_installer.a payload.o -lskarnet 

You'll now have a self-extracting executable.