Linux File Permissions: chmod and chown

Reading permissions

ls -l script.sh

Shows the permissions at the start of the line, for example -rwxr-xr--. After the first character come three sets of three: the owner, the group, then everyone else. r means read, w means write and x means execute (run).

Changing permissions with letters

chmod +x script.sh

Makes a script executable so you can run it with ./script.sh.

chmod u+x,g-w,o-r notes.txt

Gives the owner (u) execute, removes write from the group (g) and removes read from others (o).

Changing permissions with numbers

Each set is a number made by adding read (4), write (2) and execute (1). So 7 is everything, 6 is read and write, 5 is read and execute, and 4 is read only.

chmod 644 notes.txt

Owner can read and write, everyone else can only read. Normal for documents and web pages.

chmod 755 script.sh

Owner can do everything, everyone else can read and run it. Normal for scripts and folders.

chmod 600 private.key

Only the owner can read and write. Use this for private keys and passwords.

Fixing a whole folder

chmod -R changes everything inside a folder, but it treats files and folders the same, which usually isn't what you want. These two commands set folders to 755 and files to 644:

find website -type d -exec chmod 755 {} +

Sets every folder inside website to 755.

find website -type f -exec chmod 644 {} +

Sets every file inside website to 644.

Changing the owner

Changing the owner of a file needs sudo.

sudo chown roger notes.txt

Makes the user roger the owner of notes.txt.

sudo chown roger:staff notes.txt

Sets both the owner and the group.

sudo chown -R www-data:www-data /var/www/html

Gives the web server user ownership of a website folder and everything in it.

Quick reference