Add user to existing Group

Question

I want to add the Apache user (www-data) to the audio group. I've read the man page for useradd, but I'm not having any luck. I'm running xubuntu 11.10. Here's what I'm doing:

$ sudo useradd -G audio www-data
useradd: user 'www-data' already exists

If I leave out the -G option, bash, prints the help info for useradd:

$ sudo useradd  audio www-data
Usage: useradd [options] LOGIN
Options: -b, --base-dir BASE_DIR       base directory for the home directory...

It's not clear to me from the man page what options I should select to make this work.

Answer 1

The useradd command will not surprisingly try to ad a new user. To modify an existing user, like adding that user to a new group, use the usermod command.

Try this:

sudo usermod -a -G audio www-data

Answer 2

I normally use

sudo gpasswd -a myuser mygroup

Answer 3

Adding a user to a group:

sudo adduser user group

Removing a user from a group:

sudo deluser user group

Answer 4

After adding to a existing user:

usermod -a -G group user  

You may need to log out an login to get the groups permissions from /etc/group.