Editing Plan 9 from Bell Labs (section)

=== Unix compatibility ===
Though Plan 9 was supposed to be a further development of Unix concepts, compatibility with preexisting Unix software was never the goal for the project. Many [[command-line utilities]] of Plan 9 share the names of Unix counterparts, but work differently.<ref name="unix-plan9-command-translation" />

Plan 9 can support [[POSIX]] applications and can emulate the [[Berkeley socket interface]] through the [[ANSI/POSIX Environment]] (APE) that implements an [[runtime environment|interface]] close to [[ANSI C]] and [[POSIX]], with some common extensions (the native Plan 9 C interfaces conform to neither standard). It also includes a POSIX-compatible shell. APE's authors claim to have used it to port the [[X Window System]] (X11) to Plan 9, although they do not ship X11 "because supporting it properly is too big a job".<ref name="docs-ape" /> Some Linux binaries can be used with the help of a "linuxemu" (Linux emulator) application; however, it is still a work in progress.<ref name="linuxemu" /> Vice versa, the [[Vx32]] virtual machine allows a slightly modified Plan 9 kernel to run as a user process in Linux, supporting unmodified Plan 9 programs.{{r|vx32}}