很多现代的UNIX操作系统实现了一个多对一的模型，用来映射用户空间的线程到系统内核对象。
Many modern UNIX operating systems implement a many-to-few model when mapping user-level threads to kernel entities.
每一个重要的内核对象，比如每个文件系统对象和每个进程，都有一个关联到它们的“安全上下文(security context)”。
Every critical kernel object, such as every filesystem object and every process, has a "security context" associated with them.
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