Here’s the syntax for CHanging permissions or MODe — also known as chmod — for files and directories:

chmod [permissions] /path/to/file/or/directory

The three possible users are:

• file owner
• group of authorized users
• everyone else (a.k.a. “the world”)

The possible actions (and associated binary values) are:

• 4: read
• 2: write
• 1: execute

Total the values for all actions a given user has permission to perform, for each of the three users. Use “0” to indicate no permissions.

Let’s say I have a directory /var/www/vhosts/my_website/tmp and I want to assign the following permissions to it:

• owner: read / write / execute (4 + 2 + 1 = 7)
• groups: read / execute (4 + 1 = 5)
• others: no permissions (0)

Here’s the command I’d run:

chmod 0750 /var/www/vhosts/my_website/tmp

Add the -R flag to apply these permissions recursively (i.e. to all files and directories inside):

chmod -R 0750 /var/www/vhosts/my_website/tmp

It’s a best practice to employ the principle of least privilege when assigning permissions so start closed and slowly open, avoiding “world writable” at all costs.

Need more info on permission levels?