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Sparky1
Asked: 2011-11-16 10:21:54 +0800 CST

How to add existing user to an existing group?

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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 use to make this work.

users

8 Answers

  1. Best Answer

    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.
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  2. Adding a user to a group:

    sudo adduser user group

    Removing a user from a group:

    sudo deluser user group
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  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.

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  4. I normally use

    sudo gpasswd -a myuser mygroup
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  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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  6. sudo usermod -a -G groupName userName

    will work just fine, but I had to reboot entirely, just log out and log in again did not do the job...

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  7. 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.

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  8. To permanantely add a user to a group, run this command:

    sudo usermod -a -G <groupname> <username>

    Then log out and log in again (or reboot if necessary).

    Explanation:

    The usermod command will modify the /etc/group file to list the specified username in the line relevant to that group. If you run grep <groupname> /etc/group, you should see your username in the output.

    In Linux, every process is assigned to a user and groups, and any child processes inherit the user and groups of the parent process. So, for this change to take effect and propogate, you need to log out and log in again (at which point /etc/group is read and used). On Wayland, I've found that a full reboot is necessary.

    If you run the command groups, you can see if the current process has the expected groups or not.

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