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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.

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4 Answers 4

up vote 151 down vote accepted

The useradd command will not surprisingly try to add 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 groupName userName

The user will need to logout and log back in to see their new group added.

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sudo usermod -a -G [group-name] [user-name] : Just a quickie for those who only glance at the answer after reading the headline –  Programster Nov 11 '13 at 14:50
What does the -a do? It seems to be depreciated / doesn't work with it but the command works with it removed. I can't seem to find reference in a few versions of man... but, I have seen it in so many examples - what does it do? –  wilhil Aug 9 '14 at 1:05
I think the preferred way now is sudo adduser user group. It is simpler and cleaner syntax. See the response from @Bai. –  ctbrown Aug 14 '14 at 14:20

Adding a user to a group:

sudo adduser user group

Removing a user from a group:

sudo deluser user group
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not exactly what this question being asked for –  Tejendra Sep 3 '14 at 8:10

I normally use

sudo gpasswd -a myuser mygroup
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usermod was not available on my system ubuntu 14.04. This worked great! –  Drew Jun 24 '14 at 15:45

After adding to a existing user:

usermod -a -G group user  

You may need to logout and login to get the groups permissions from /etc/group.

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Please make it the part "need to logout and login" bold. –  Jin Kwon Dec 17 '13 at 6:36
FYI: I think the id command should indicate you were added to the group without needing to exit. id myuser –  ficuscr Jan 3 '14 at 16:57

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