uname产生的缺省输出是基本操作系统名称，如Linux或Solaris。
The default output from uname is the base operating system name, such as Linux or Solaris.
如果指定的名称在操作系统中只定义为用户，或者没有定义，那么假设是USER。
If the specified name is defined in the operating system only as user or if it is undefined, user is assumed.
如果指定的名称在操作系统中同时定义为用户和组，那么返回一个错误。
If the specified name is defined in the operating system as both, an error is returned.
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