sysroot

A sysroot is a directory that serves as the root directory of a target system for the purposes of building software. It provides the headers, libraries, and basic filesystem layout that a cross-compiler or build toolchain assumes when producing binaries for that target. The sysroot allows developers to compile against a target’s interfaces without requiring a live, running system on the same machine.

During compilation, the compiler uses the sysroot to locate include files and libraries. A typical sysroot contains paths such as SYSROOT/usr/include and SYSROOT/lib or SYSROOT/lib64, mirroring the layout of a real root filesystem. The linker uses the libraries found in the sysroot to resolve runtime dependencies. The sysroot is especially important in cross-compilation, embedded development, and when building packages for a distribution.

Creating and maintaining a sysroot can be done with various tools and workflows. Debian-based systems may use debootstrap or sbuild, while embedded workflows frequently rely on Buildroot or the Yocto Project. The Android NDK also ships with a dedicated sysroot for its API levels. A sysroot is often read-only and kept separate from the host filesystem to keep host and target toolchains isolated and reproducible.

Relation to chroot: a sysroot is not a chroot. It is a path used by the compiler and toolchain to locate files for a target, rather than an actual isolated running environment. It can be used inside a chroot, but does not by itself provide process isolation. Ensuring ABI compatibility and matching toolchain components is essential for successful builds.

In summary, sysroot is a build-time construct that models a target’s root filesystem to enable cross-compilation and packaging without requiring a full target environment.