entityMap|blocks|key|67nsp|text|区分真实用户id和有效用户id是因为您可能需要临时获取另一个用户的身份(大多数情况下，这将是|type|unstyled|depth|inlineStyleRanges|entityRanges|data|f0ukb|，但它可以是任何用户)。如果您只有一个用户id，那么以后就没有办法改回原来的用户id了。|9dd56|，使用|13irb|更改为任何用户的权限)。|flo9l|因此，真正的用户id是您的真实身份(拥有该进程的人)，而有效的用户id是操作系统查看以决定是否允许您执行某项操作的内容(大多数情况下，有一些例外)。|fu1lj|当您登录时，登录shell将真实和有效的用户id设置为与密码文件提供的值(真实用户id)相同的值。|d9t5|现在，您还可以执行setuid程序，并且除了以另一个用户身份运行之外(例如，|b9a9o|)+setuid程序是|8b4i1|还有|5dgt6|应该为你做点什么。这是如何工作的？|56nqg|在执行setuid程序之后，它将拥有您的真实id+(因为您是进程所有者)和文件所有者的有效用户id+(例如|5868k|)，因为它是setuid。|c3pk1|这个程序使用超级用户权限做它需要做的任何事情，然后想要代表你做一些事情。这意味着，尝试做一些你不应该做的事情|ddp9o|应该失败|79ieu|..。它是如何做到这一点的？显然，通过将其有效的用户id更改为真实的用户id！|42ahn|现在setuid程序没有办法切换回来，因为内核只知道你的id和...|f8cpj|您的id|bh3qh|..。邦，你死定了。|9bhc0|这就是保存的set-user+id的用途。^0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0^^$0|$]|1|@$2|3|4|5|6|7|8|1C|9|@]|A|@]|B|$]]|$2|C|4|D|6|7|8|1D|9|@]|A|@]|B|$]]|$2|E|4|F|6|7|8|1E|9|@]|A|@]|B|$]]|$2|G|4|H|6|7|8|1F|9|@]|A|@]|B|$]]|$2|I|4|J|6|7|8|1G|9|@]|A|@]|B|$]]|$2|K|4|L|6|7|8|1H|9|@]|A|@]|B|$]]|$2|M|4|N|6|7|8|1I|9|@]|A|@]|B|$]]|$2|O|4|P|6|7|8|1J|9|@]|A|@]|B|$]]|$2|Q|4|R|6|7|8|1K|9|@]|A|@]|B|$]]|$2|S|4|T|6|7|8|1L|9|@]|A|@]|B|$]]|$2|U|4|V|6|7|8|1M|9|@]|A|@]|B|$]]|$2|W|4|X|6|7|8|1N|9|@]|A|@]|B|$]]|$2|Y|4|Z|6|7|8|1O|9|@]|A|@]|B|$]]|$2|10|4|11|6|7|8|1P|9|@]|A|@]|B|$]]|$2|12|4|13|6|7|8|1Q|9|@]|A|@]|B|$]]|$2|14|4|15|6|7|8|1R|9|@]|A|@]|B|$]]|$2|16|4|17|6|7|8|1S|9|@]|A|@]|B|$]]|$2|18|4|19|6|7|8|1T|9|@]|A|@]|B|$]]|$2|1A|4|1B|6|7|8|1U|9|@]|A|@]|B|$]]]]

The distinction between a real and an effective user id is made because you may have the need to temporarily take another user's identity (most of the time, that would be <code>root</code>, but it could be any user). If you only had one user id, then there would be no way of changing back to your original user id afterwards (other than taking your word for granted, and in case you are <code>root</code>, using <code>root</code>'s privileges to change to any user).

So, the real user id is who you really are (the one who owns the process), and the effective user id is what the operating system looks at to make a decision whether or not you are allowed to do something (most of the time, there are some exceptions).

When you log in, the login shell sets both the real and effective user id to the same value (your real user id) as supplied by the password file.

Now, it also happens that you execute a setuid program, and besides running as another user (e.g. <code>root</code>) the setuid program is also supposed to do something on your behalf. How does this work? 
After executing the setuid program, it will have your real id (since you're the process owner) and the effective user id of the file owner (for example <code>root</code>) since it is setuid. 

The program does whatever magic it needs to do with superuser privileges and then wants to do something on your behalf. That means, attempting to do something that you shouldn't be able to do should fail. How does it do that? Well, obviously by changing its effective user id to the real user id!

Now that setuid program has no way of switching back since all the kernel knows is your id and... your id. Bang, you're dead.

This is what the saved set-user id is for.

entityMap|blocks|key|3t7f5|text|这就是我对它的理解。用户执行的文件(相当于启动一个进程)将具有与该用户的id相等的RUID。这里需要注意的重要一点是，创建文件的uid与执行文件的uid不同。它们可以是相同的，也可以是不同的。因此，根据执行文件的UID，RUID可能会有所不同。如果文件具有setuid位，则每当uid执行该文件时，该uid将临时替换为文件所有者的uid。因此，如果我们有一个由uid+456拥有的文件，并且上面有setuid位，那么每当uid+123执行该文件时，该文件都将使用uid+456执行。在这种情况下，uid+123是RUID，uid+456是EUID。|type|unstyled|depth|inlineStyleRanges|entityRanges|data^0^^$0|$]|1|@$2|3|4|5|6|7|8|C|9|@]|A|@]|B|$]]]]

This is how I understand it. The file an user executes(equivalent to starting a process) will have a RUID equal to that user's id. Important thing to note here is that the uid which created a file is not the same as the uid that executes the file. They can be the same or different. So, RUID may vary depending on the UID that executes the file. When a file has the setuid bit on it, whenever an uid executes that file, that uid will temporary be replaced with the file owner's uid. So, if we have a file owned by uid 456 and has the setuid bit on it, whenever uid 123 executes that file, that file will be executed with the uid 456. In this scenario, uid 123 is the RUID and uid 456 is the EUID.

I am already aware of the real user id. It is the unique number for a user in the system.
On my system, my <code>uid</code> is
<pre><code>$ echo $UID
1014
$
</code></pre>
What do the other two IDs stands for?
And what is the use of effective user id and saved user id and where do we use them in the system?

Difference between Real User ID, Effective User ID and Saved User ID

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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 我已经意识到 真实用户id ..。它是系统中用户的唯一编号。 在我的系统上，我的 是 $ echo $UID1014$ 另外两个ID代表什么？ 有什么用呢？ 有效用户id 和 已保存的用户id 那么我们在系统中的什么地方使用它们呢？

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