File and Folder Permissions

PublishedAugust 29, 2020

This page contains information on the series of letters and dashes that define file and folder permissions in Linux.

Consider the following terminal output when running ls -l

-rw-r--r-- 1 root root       3028 Apr 23 02:40 adduser.conf
drwxr-xr-x 2 root root       4096 Apr 23 03:17 alternatives
drwxr-xr-x 3 root root       4096 Jun 28 21:20 apparmor
drwxr-xr-x 7 root root       4096 Jun 28 21:20 apparmor.d
drwxr-xr-x 3 root root       4096 Jun 28 21:20 apport
drwxr-xr-x 7 root root       4096 Apr 23 02:40 apt
-rw-r----- 1 root daemon      144 Nov 12  2018 at.deny
-rw-r--r-- 1 root root       2319 Feb 25  2020 bash.bashrc
-rw-r--r-- 1 root root         45 Jan 25  2020 bash_completion

The first character denotes the file type. For examples, the first character in each list is either a dash -, the letter d, or an l.

A dash - indicates that the file is a regular file.
The letter d indicates a directory file type, which is commonly referred to as a folder. A directory is a type of special file. Instead of data, it contains pointers to all of the files that are contained within the directory.
A symlink begins with a lowercase L, e.g.,

lrwxrwxrwx 1 root root      4 Dec 30 05:15 sh -> bash

Permissions Abbreviations

Permissions for files are represented by the letters r, w and x or a hyphen - character.

r if reading permitted, - if it is not.
w if writing permitted, - if it is not.
x if execution permitted, - if it is not.

Symbolic Notation Triads

The first triad is composed of the second, third and fourth characters after the file type. This show what the owner can do.

The second triad or next three characters show the permissions for the group members.

The third triad or last three characters show the permissions for the other users.

In each triad, the first character is read permissions, the second character is write permissions and the third character is execute permissions.

Numeric Notation

Another method for representing permissions is an octal (base-8) notation that consists of at least three digits.

Examples of symbolic and numeric notation

Symbolic	Numeric	Description
`----------`	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
`---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

Numbers for all permission types

Symbols	Number	Description
`---`	0	no permission
`--x`	1	execute
`-w-`	2	write
`-wx`	3	execute & write
`r--`	4	read
`r-x`	5	read & execute
`rw-`	6	read & write
`rwx`	7	read, write & execute

Resources

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