The minimum versions for each of the databases supported by Bareos are:
PostgreSQL 8.4 (since Bareos 13.2.3)
MySQL 4.1 - 5.6 or compatible fork (e.g. MariaDB), see MySQL/MariaDB Support
Windows release is cross-compiled on Linux
Bareos requires a good implementation of pthreads to work. This is not the case on some of the BSD systems.
The source code has been written with portability in mind and is mostly POSIX compatible. Thus porting to any POSIX compatible operating system should be relatively easy.
Bareos Version >= 15.2.0 offers a JSON API mode, see Bareos Developer Guide (api-mode-2-json). On some platform, the Jansson library is directory available. On others it can easly be added. For some older platforms, we compile Bareos without JSON API mode.