Linux file Permissions (r, W, X, S, T, I, a) detailed

WX needn't elaborate. Focus on the S, T, I, a rights

S: The file owner and group set SUID and GUIDs, and the files are executed as root after the S permission is set. When the S permission is set, the file owner or group must first set the appropriate X permissions. Otherwise, s permission does not actually take effect (c h m o d command does not perform the necessary integrity checks, even if you do not set the X permission to set the S permission, chmod will not complain, when we ls-l see RWS, the capital S to explain the rights did not take effect). Linux to modify the password passwd is a set of Suid program, ordinary users do not read and write/etc/shadow file permissions can modify their password.

ls-al/usr/bin/passwd

-RW s r-xr-x 1 root 32988 2008-12-08 17:17/usr/bin/passwd

We can set the S permission via character mode: chmod a+s filename, or you can set it using absolute mode:

Set S u i d: the one before the corresponding permission bit is set to 4;
Set g u i d: Set the one before the corresponding permission bit to 2;
Both sets the bit: the one before the corresponding permission bit is set to 4+2=6.

Such as:

chmod 4 764 filename//Set SUID

T: set sticky bit, a file can read and write to the user and must have to let him have the right to delete this file, if the file set the T permission only the owner and Root have the right to delete files, through chmod +t filename to set t permissions.

I: Can not modify the permission example: chattr u+i filename file can not be modified, regardless of anyone, if you need to modify the need to delete the first I permission, with chattr-i filename on it. To see if the file has set I permissions with lsattr filename.

A: Only append permissions, for the log system is very good, this permission to the target file can only append, cannot delete, and can not be appended through the editor. You can use Chattr +a to set additional permissions

After you log on to Linux as root, you can see it after you enter "Ls-al" on the command line:

[Root@www ~]# Ls-al
Total 156
Drwxr-x---4 root 4096 Sep 8 14:06.
Drwxr-xr-x root root 4096 Sep 8 14:21.
-RW-------1 root 1474 Sep 4 18:27 anaconda-ks.cfg
-RW-------1 root 199 Sep 8 17:14. bash_history
-rw-r--r--1 root is 6 2007. Bash_logout
-rw-r--r--1 root root 191 6 2007. Bash_profile
-rw-r--r--1 root root 176 6 2007. BASHRC
-rw-r--r--1 root is 6 2007. CSHRC
DRWX------3 root 4096 Sep 5 10:37. gconf <= Example Description Office
DRWX------2 root 4096 Sep 5 14:09. gconfd
-rw-r--r--1 root 42304 Sep 4 18:26 install.log <= Example Description Office
-rw-r--r--1 root 5661 Sep 4 18:25 Install.log.syslog
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Permissions Link [Owned by] Group [File Capacity] [Date Modified] [? n name]