Linux File Attribute Awareness

Linux system is a typical multi-user operating system, different users are in different positions, have different permissions, we can view through the Ls-l

[Email protected] cron.daily]# ll/total 104dr-xr-xr-x.   2 root root 4096 Sep 11:15 bindr-xr-xr-x. 4 root root 4096 Sep 10:03 boot ...

In the above, the first property of bin is denoted by D, and "D" is the meaning of the directory file in the Linux system.

Careful observation we can see a total of 11 characters, the first character will appear as follows:

Start with "D": Catalog file

"-" begins with: file

"L" Start: Soft Connection file

Start of "B": Block device

"C" Start: Character device

The following 10 for the characters are represented separately:

Dr-xr-xr-x. : User Rights

Dr-xr-xr-x. : Group Permissions

Dr-xr-xr-x. : Other user rights

dr-xr-xr-x . :     hidden ACL permissions

It is often mentioned that 777 of the highest permissions, 755/644 permissions, in fact, are easy to understand, we add and subtract to associate:

Let's first define the associated permission rules:

R-->read=4 All rights

w-->write=2 Write permissions

X-->excute=1 Execute Permissions

So what does 777 mean?

The first 7 is calculated as the above rule equals those added? The answer is obvious 4+2+1=7

So what's the second one? What about the third one? Is it easy to understand that it is the permissions of the 4+2+1= group 4+2+1= the rights of other users to integrate them together? Not just rwxrwxrwx so easy!.

What about 755? Rwxr-xr-x 644? rw-r--r-- Note that the first character--is that the file behind it is empty, that is, no meaning.

The right to introduce, we introduce the next

Dr-xr-xr-x. 2 root root 4096 Sep 11:15 bin

What are the 2 root root 4096, respectively?

[[email protected] jr855]# lltotal 0-rw-r--r--.  1 root root 0 sep 22 16:56 11.txt[[email protected] jr855]#  ln -s 11.txt 1.txt[[email protected] jr855]# lltotal 0-rw-r--r--.  1 root root 0 Sep 22 16:56 11.txtlrwxrwxrwx. 1 root  root 6 sep 22 17:47 1.txt -> 11.txt[[email protected] jr855]#  ln 11.txt 2.txt[[email protected] jr855]# lltotal 0-rw-r--r--.  2  root root 0 sep 22 16:56 11.txtlrwxrwxrwx. 1 root root  6 sep 22 17:47 1.txt -> 11.txt-rw-r--r--.  2 root root  0 sep 22 16:56 2.txt[[email protected] jr855]# 

The above earnest discovery, the clever you may have discovered the mystery, the soft connection does not increase his number (Ln-s for soft connection, we can also find "L" from the first bit)

-rw-r--r--. 1 root root 0 Sep 16:56 11.txt Here 11.txt is a file and represents the user root and group root It's permissions are 644, normal people understand that users can read and write cannot be executed, Groups can be read and not written, other users can read and write

At this point, the simple file attributes are complete.

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Linux File Attribute Awareness