How permissions are assigned?

How permissions are assigned?

The basic format of chmod is: chmod xyz file
The xyz represent value that goes from 0-7; each number represents permissions in a group.

For instance:

x	would be for the owner of the file
y	would be for the group that owns the file(group the user belongs to)
z	would be for everybody
file	name of the file being modified

Refer to the following table for a better understanding

Number	Permissions
0	None = can not read, write or execute
1	Can execute, but can not read or write
2	Write only, can not read or execute
3	Can write, can execute
4	Read only, can not write to or execute
5	Read only, executable, can not write to
6	Writeable, readable file, but not executable
7	Readable, writeable and executable file

There are several ways to give permission to a file as you could see on the last two tables. You could basically use any part of the table to assign these permissions.

Example
I will use the numerical part of the first table to assign permission to an html file that can be viewed over the Internet.

[root@server2 collections]#chmod 644 internal.html

How I determined that? I simply added 400+200+40+4 = 644 from table 3.2

• Read by owner
• Write by owner
• Read by group
• Read by others

If I do an ls –l that would look like this:

[root@server2 collections]#ls –l

total

-rw-r--r-- 1 root root 6 Aug 17 09:09 afile

-rw-r--r-- 1 root root 19 Aug 18 12:47 internal.html

[root@server2 collections]#

What would happen if I make that writeable by others (I would be a dumb administrator), but for demonstration purposes lest make that file writeable by others.

[root@server2 collections]# chmod 646 internal.html
Now I do an: ls –l

[root@server2 collections]#ls –l

total

-rw-r--r-- 1 root root 6 Aug 17 09:09 afile

-rw-r--rw- 1 root root 19 Aug 18 12:47 internal.html

[root@server2 collections]#

Now internal.html is world writeable…be careful how you assign permissions. Normally, don't leave a file as 777 (that is full access to the file), anyone can replace or delete it.