there are at least four common implementations of "hostname" on Linux: debian, coreutils, net-tools, busybox, and arguably toybox. there are also at least four

there are at least four common implementations of "hostname" on Linux: debian, coreutils, net-tools, busybox, and arguably toybox. there are also at least four implementations of su (util-linux, shadow, busybox, toybox) and five implementations of kill (coreutils, procps(-ng), util-linux, busybox, toybox).