文件权限, 关于chmod
Marine_blitz
posted @ Sep 28, 2010 04:20:01 PM
in Marine Ever Felt
, 2202 readers
首先可以通过ls来观看文件的权限, 文件权限是长成这个样子的:
drwxr-xr-x 3 marine marine 4096 2010-09-22 20:43 lib
drwxr-xr-x 4 marine marine 4096 2010-06-22 18:45 man
-r--r--r-- 1 marine marine 28230 2010-06-22 16:43 README.html
-r--r--r-- 1 marine marine 25317 2010-06-22 16:43 README_ja.html
以上的第一段就是
第二段是硬链接数目，一般文件都只有一个吧。
文件权限是这样看的：
[类型标记][User/Owner][Group][Other]
用u标记用户,g标记组，o标记其他用户，而a则等效于ugo，即全部。显然root用户是无视这些权限的。
类型标记占一位，比如d表示文件夹，-表示普通文件，l表示软链接，然后是三组三位布尔数据，表示的是特定用户对该文件的操作权，按[读，写，运行/特殊]的格式排列。
所以你在用chmod的时候，可以用数字，或者直接用标记号来调节文件的权限。
比如:
chmod u+x a.out -> 如此作为用户的你就可以运行a.out了
chmod a+x lib -> 如此你就可以以任何解除删除lib下的链接了
chmod u-x a.out -> 去掉运行权限
chmod ugo=rwx a.out -> 直接设置所有人对a.out的所有操作权 这个命令等效于 chmod 777 a.out ，显然三位二进制的最大值是7.
然后要说的是粘住位。在远古时代，Linux是没有虚拟内存机制的，而需要你手工指定那些文件在运行完之后要留在交换区，如此你可以通过设置站住位来搞定它，这就是chmod的第一个数字，比如chmod 1777 a.out:
marine@marine-thinkpad:~$ touch a.out
marine@marine-thinkpad:~$ ls
a.out
marine@marine-thinkpad:~$ sudo chmod 1777 a.out
[sudo] password for marine:
marine@marine-thinkpad:~$ ls -l
-rwxrwxrwt 1 marine marine 0 2010-09-28 08:34 a.out
最后的t就是这个功能了,当然，现在的粘住位的这一功能已经基本没用了，而他表达的意思是，除了该文件的所有者(创建或者chown)，都不能删除这个文件(因为原先这个权限是所在目录给予的)
而特殊的功能位还有setgid 和setuid，他们的第一位数字分别是2和4，当然上述也可以通过u+s，g+s，o+t来指定,setgid和setuid的意义是，无论你是那个组(那个用户)，都能够像属主那样去操作文件，因为你会被set成这个文件的所有人/组。
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