There are three sets of permissions to worry about with any directory/file:
- User — What the owner of the file can do
- Group — What users of the same group can do
- Other — What anyone else can do
Correspondingly, users have a username (unique to each user). Users can also be part of a group — In fact, multiple users can be part of the same group.
chmodcommand can accept numeric integers, such as 0664, which relate to user permissions. See this to help create these, if you wish
I will cover using chmod. Chmod is used to modify the permissions of a directory or file.
chmod -flags permissions /path/to/dir/or/file
chmod -R … will recursively go through the directory provided and change all file/directory permissions as specified.
You can define for whom the permissions you are setting apply with these:
- u = user
- g = group
- o = other
You can add or remove permissions using these:
- + will add permissions
- - will remove permissions
You can set these permissions:
- r = read
- w = write
- x = execute
Use this knowledge to setup Apache
- Apache is run as user www-data and group www-data.
- Server web root is /var/www
We need to set the owner/group of the web root (and any directories/files therein):
$ sudo chown -R www-data:www-data /var/www
We need to setup the proper permissions for users and groups. We do some blanket commands restricting access, and then open access up as much as we need to.
To start, make it so no-one but the current user (www-data) can access the web-root content. We use ‘go’, meaning apply to ‘group’ and ‘other’. We use ‘-’, which means remove permissions. We use ‘rwx’ to remove read, write and execute permissions.
$ chmod go-rwx /var/www
Next, allow users of the same group (and ‘other’) to enter the
/var/www directory. This is not done recursively. Once again, we use ‘group’ and ‘other’ but we use ‘+’ to allow the execute (‘x’) permission.
$ chmod go+x /var/www
Next, change all directories and files in the web root to the same group (www-data) — just in case there are files in there currently:
$ chgrp -R www-data /var/www
Next, let’s do another “reset” of sorts — Make it so only the user can access web content:
$ chmod -R go-rwx /var/www
And finally, make it so anyone in the same group can ready/write and execute directories/files in the web root.
$ chmod -R g+rx /var/www
I actually give group write permissions as well, for users which need to modify content, such as users used to deploy code. That looks like this:
$ chmod -R g+rwx /var/www
Often going through all of these steps isn’t necessary, but this is a useful exercise to see how these commands work!