The Over-Simplified Guide to Reading Linux Permissions You’ve Been Looking For

I had to draw this up for a co-worker today. I didn’t want to waste his time with metaphors and other nonsense. I wanted it to ‘click’. He wanted to know how drwx------ came out to ‘700’. This is what I came up with.

Examples

Linux permissions are displayed in 10 characters, like this:

drwxrwxrwx

The first character is the type of resource. Here are 3 common types you might encounter.¹

File	f
Directory	d
Link	l

The last nine are really groups of three.

User	Group	Other
rwx	rwx	rwx

rwx have integers attached to them.

Letter	Function	Value
r	Read	4
w	Write	2
x	Execute	1

How it adds up

rwx = 7	because	4 + 2 + 1 = 7
rw- = 6	because	4 + 2 = 6
r-x = 5	because	4 + 1 = 5

Full Example:

drwxr-xr-x

Type	User	Group	Other
d	rwx	r-x	r-x
	7	5	5

¹Special thanks to cantonboy329. I re-phrased this so that it can be accurate without going into too much detail.