user permissions id

基本解释

The Linux permissions model has two special access modes called suid (set user id) and sgid (set group id).
Linux 权限模型有两个特殊的访问模式，名为 suid（设置用户 id）和 sgid（设置组 id）。
The system sets permissions for all the files in an application so that only the user ID assigned to that application can access them.
应用中的所有文件访问许可都被系统设置了此 ID，因此，只有被分配了该用户ID的应用可以访问这些文件。
Because the numeric IDs of logins are reused, a future login ID will very likely be assigned this numeric ID, and mistakenly gain the permissions of the user ID.
由于登录的数字ID重复使用，未来的登录ID很可能会分配此数字ID，并错误地获得对用户ID的权限。
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