CXXI. YP/NIS Functions
NIS (formerly called Yellow Pages) allows network management of important administrative files (e.g. the password file). For more information refer to the NIS manpage and The Linux NIS(YP)/NYS/NIS+ HOWTO. There is also a book called Managing NFS and NIS by Hal Stern.
None besides functions from standard Unix libraries which are always available (either libc or libnsl, configure will detect which one to use).
由于这些常量是由该扩展模块定义的，因此只有在该扩展模块被编译到 PHP 中，或者在运行时被动态加载后，这些常量才有效。