Linux – Give a group write permission to a folder

file-permissionslinuxpermissionsUbuntuuser-groups

I need help understanding how giving write permission to a group, works in Ubuntu. I am logged in as root and have a www-data:www-data and ftpuser:ftpuser (user:group). I add the ftpuser into the www-data group using:

usermod -a -G www-data ftpuser

Now my www-data group has two users.

I then make the group www-data, owner of the folder /var/www using:

chgrp -R www-data /var/www

Still i have no write ability to the folder by a group member (though the group owns it) unless i give write permissions to the group. Now according to this best answer i also need to set the permissions to the directory using sudo chmod -R 770 /path/to/the/directory and this is what confuses me.

If a user is the owner of a directory why can't he write to it?
Can a user of a group give the group write permissions to a folder owned by the group himself?
Where is the group defined in the command sudo chmod -R 770 /path/to/the/directory ? Won't this give recursive permissions to all users?

Best Answer

though the group owns it

No, group does not own a file in a sense that the permissions for owner apply. Owner permissions apply only to owner - the user; and group permissions apply to the assigned group.

If a user is the owner of a directory why can't he write to it?

He can, except that ftpuser in your case is not the owner.

Most likely, because you don't say it explicitly: root or www-data is the owner /var/www of the file, and ftpuser is a member of the group www-data.

Even if the user www-data and the group www-data have the same name, they are different entities for the operating system.

Can a user of a group give the group write permissions to a folder owned by the group himself?

Again: folder is not owned by a group. If the group has write-permission, any member of the group can change the permissions to the object.

Where is the group defined in the command sudo chmod -R 770 /path/to/the/directory

The second 7 refers to the group permissions (7 is a combination of read, write, and execute).

Won't this give recursive permissions to all users?

It will assign (recursively):

  • read, write, and execute for the owner (first 7)
  • read, write, and execute for the group (second 7)
  • no permissions for other users (last 0)
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