Meaning of Linux permissions

What are permissions?

# ls -la ~
dr-xr-x---. centos centos 4096 May   4 09:11 .

The description of dr-xr-x --- at the time of doing something is permission.

--File access rights --Controls the execute permission of sh and the write permission by PHP.

Actually I use it without knowing it well

I've been doing PG for a long time, but I haven't really investigated it. (Because it was a stray PG, I have never studied properly) It ’s squid. That's why I asked the person at work, so I make a memorandum

The meaning of each character

There are three types of first characters: `-`, `d`, and `l`.

letter	meaning
-	File
d	directory
l	Symbolic link

The following 9 characters `r`, `w`, and `x` can be replaced with numbers, respectively.

letter	Numbers	meaning
r	4	Read permission
w	2	Write permission
x	1	Execution authority
-	0	No authority

The sequence of letters is meaningful

--Yo with 3 character delimiters ―― ʻOwner ʻOwnerGroup ʻOther are arranged in this order. ―― ʻOwner It is the authority to allow the owner himself. --ʻOwnerGroup This is the authority to allow the group to which the owner belongs. ―― ʻOther It is the authority to allow other users.

The numbers are meaningful

--For example, if you say chmod 700 ., it will bedrwx ------. --In other words, the character value is specified as a numerical value. --In the case of the example, r + w + x is used to add up to 7, and the following is set to 00 to make it-.

I see

Let's remember it properly.