How to add existing user to an 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 use to make this work.

Solution 1

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 -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.

In general (for the GUI, or for already running processes, etc.), the user will need to log out and log back in to see their new group added. For the current shell session, you can use newgrp:

newgrp groupName

• newgrp adds the group to the current shell session.

Solution 2

Adding a user to a group:

sudo adduser user group

Removing a user from a group:

sudo deluser user group

Solution 3

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.

Solution 4

I normally use

sudo gpasswd -a myuser mygroup

Solution 5

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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Comments

[Programster]

sudo usermod -a -G [group-name] [user-name] : Just a quickie for those who only glance at the answer after reading the headline

[ficuscr]

FYI: I think the id command should indicate you were added to the group without needing to exit. id myuser

[Drew]

usermod was not available on my system ubuntu 14.04. This worked great!

[wilhil]

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?

[ctbrown]

I think the preferred way now is sudo adduser user group. It is simpler and cleaner syntax. See the response from @Bai.

[Tejendra]

not exactly what this question being asked for

[Adam D.]

Logging out and back in was required for me on Ubuntu 14.10.

[sage]

@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.

[Adam Michalik]

@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."

[con-f-use]

Is there a way to get around the "logout and back in" part? Some type of update-groups command, maybe?

[knocte]

this is debian/ubuntu specific?

[Auspex]

This is exactly the question being asked. @knocte, yes, I think it is Debian specific

[Stibu]

@Auspex I can confirm that it does not work on Red Hat.

[Aaron McDaid]

@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

[stenix]

You can use the newgrp [group-name] command to add a new group to the user of the current session without logging out and in again. Only the current session will be affected though.

[russoue]

@AaronMcDaid, thanks for the nice tip! There are situations when logging out is not an option and your tip saved me some troubles!

[vhs]

This worked great on Debian Stretch too, where usermod was not installed.

[user643605]

Another option to apply the group membership is sudo login -f <username>, as per Aaron McDaid's comment on another answer.

[klaas]

@con-f-use: I think a su - USERNAME will directly activate a new shell with the new groups settings available. From the docs: SYNOPSYS: su [options] [-] [user [argument...]] DESCRIPTION su allows commands to be run with a substitute user and group ID. The - is a short form for the loginparameter.

[Flimm]

Remember to log out and in again.

[Flimm]

I found this too, and I wonder if it's because I'm running Wayland.