Unlike many other projects porting conventional Linux distributions to Android phones, postmarketOS does not use the Android build system or userspace.[16] Each phone has only one unique package, and flashable installation images are generated using the pmbootstrap tool.[4] The project intends to support the mainline Linux kernel on all phones in the future, instead of the often outdated Android-specific fork, to reduce the potential for security exploits.[4] A few devices can boot into the mainline kernel already.[17][18] The project aims to support Android apps, originally through the use of Anbox, which was replaced by Waydroid since postmarketOS v21.12.[19][20]

Alpine Linux was chosen as the base distribution due to its low storage requirements, making it more suitable for older devices. Excluding the kernel, a base installation takes up approximately 6 MB.[21][4][22] In March 2024, the maintainers announced that postmarketOS would migrate from OpenRC to systemd as its init system for select user interfaces.[23]