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 use to make this work.

up vote 909 down vote accepted

The useradd command will try to add a new user. Since your user already exists this is not what you want.

Instead: 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 log out and log back in to see their new group added.

  • The -a (append) switch is essential. Otherwise, the user will be removed from any groups, not in the list.

  • The -G switch takes a (comma-separated) list of additional groups to assign the user to.

  • 66
    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
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    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
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    @wilhil: man usermod: "-a, --append - Add the user to the supplementary group(s). Use only with the -G option.; -G, --groups GROUP1[,GROUP2,...[,GROUPN]]] [...] If the user is currently a member of a group which is not listed, the user will be removed from the group. This behaviour can be changed via the -a option, which appends the user to the current supplementary group list." – Adam Michalik Jan 26 '16 at 15:03
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    Is there a way to get around the "logout and back in" part? Some type of update-groups command, maybe? – con-f-use Mar 19 '16 at 0:05
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    @con-f-use, if you can run sudo login -f YOURUSERNAME, it will start a new shell session. Use the id command to verify that the new session is in the correct set of groups. However, this isn't "global" - it doesn't apply to terminals that are already open. So, really, logging out is the best option, where possible – Aaron McDaid Mar 31 '17 at 14:57

Adding a user to a group:

sudo adduser user group

Removing a user from a group:

sudo deluser user group
  • 2
    not exactly what this question being asked for – Tejendra Sep 3 '14 at 8:10
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    @Tejendra's comment seems to presuppose that using useradd is desirable/mandatory to answer OP's question; Perhaps this answer is just missing words to indicate that adduser/deluser is a better alternative. – sage Jul 28 '15 at 19:39
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    For me simpler interface is better, that's why I like this one. – Betlista Aug 11 '16 at 10:35
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    This is exactly the question being asked. @knocte, yes, I think it is Debian specific – Auspex Nov 14 '16 at 12:58
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    @Auspex I can confirm that it does not work on Red Hat. – Stibu Feb 22 '17 at 9:43

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.

  • 21
    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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    Logging out and back in was required for me on Ubuntu 14.10. – A.Danischewski Apr 1 '15 at 0:32

I normally use

sudo gpasswd -a myuser mygroup
  • 3
    usermod was not available on my system ubuntu 14.04. This worked great! – Drew Jun 24 '14 at 15:45

On Ubuntu, since logging in as root is not enabled, users in the sudo group can elevate privileges for certain restricted commands. Any restricted command must be prepended with sudo to elevate privilege.

sudo usermod -a -G group user

will add the existing user user to a supplemental group named group. The user's primary group will remain unchanged.

I'm posting this as an answer because I don't have enough reputation to comment. As @dpendolino's mentioned, for the effects of this command to persist:

sudo usermod -a -G groupName userName

...you need to logout/login again.

However, if you need a shortcut to start using your new group membership immediately (and you have the correct sudo privileges) I have found this work-around:

$ sudo su -
# su [userName]
$ groups

Explanation:

  • sudo su - will give you a root shell
  • su [userName] returns you to a shell with your user
  • groups when run now will show the group you added with the usermod -aG command

In my case I was trying to add the 'docker' group to my user

Before:

$ groups
userName adm cdrom sudo dip plugdev lpadmin sambashare wireshark lxd

After:

$ groups
userName adm cdrom sudo dip plugdev lpadmin sambashare wireshark lxd docker

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