File System Permissions

Unix-based Systems

-: doesn’t allow
r: allows read
w: allows write
x: allows execute, or on directories, allows access to contents

Number	Permission	Symbolic Notation
0	None	`—`
1	Execute only	`–x`
2	Write only	`-w-`
3	Execute and write (1 + 2 = 3)	`-wx`
4	Read only	`r–`
5	Read and execute (4 + 1 = 5)	`r-x`
6	Read and write (4 + 2 = 6)	`rw-`
7	Read, write, and execute (4 + 2 + 1 = 7)	`rwx`

permission groups

	owner	group	others
read	r - -	r - -	r - -
write	- w -	- w -	- w -
execute	- - x	- - x	- - x

Symbolic Notation	Numeric Notation	English
`----------`	0000	no permissions
`-rwx------`	0700	read, write, & execute only for owner
`-rwxrwx---`	0770	read, write, & execute for owner and group
`-rwxrwxrwx`	0777	read, write, & execute for owner, group and others SECURITY RISK
`---x--x--x`	0111	execute
`--w--w--w-`	0222	write
`--wx-wx-wx`	0333	write & execute
`-r--r--r--`	0444	read
`-r-xr-xr-x`	0555	read & execute
`-rw-rw-rw-`	0666	read & write
`-rwxr-----`	0740	owner can read, write, & execute; group can only read; others have no permissions

Numeric Notation: octal integer, precedes the number with a 0 (zero), e.g. 0644

Directory and File Permissions

Permissions	Directory	File
Most secure	`755`	`644`
Least secure	`777`	`666`

Directories need to allow for access to their contents, so for each scope (owner, group, world), directory permissions will nearly always be one of the execute permissions: 1, 3, 5, or 7.

In a web application, no files themselves need execute privileges because the web server is controlling the process that actually executes the PHP. So the typical options will be 4 or 6.

Usually only the owner needs write permissions, and group/world just need read.