How to remove a user from one or more groups in Linux

In Linux and other multi-user systems, users gain access to specific privileges based on the groups they belong to. If a user's real-world role changes, their group memberships within the system should be updated accordingly. This may involve adding the user to new groups or removing them from existing ones.

Linux stores local user and group information in the /etc/passwd and /etc/group files. While it is possible to remove users from groups by editing these files, doing so is risky as a misconfiguration could render the entire system inoperable.

Instead, you can use the usermod utility to change a user's primary group and the gpasswd utility to remove a user from a group. Both of these command-line tools are included by default in all Linux distributions.

1. Open the terminal.
2. Retrieve the list of users on your system.

   $ getent passwd
   root:x:0:0:root:/root:/bin/bash
   daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin
   bin:x:2:2:bin:/bin:/usr/sbin/nologin
   sys:x:3:3:sys:/dev:/usr/sbin/nologin
   sync:x:4:65534:sync:/bin:/bin/sync
   games:x:5:60:games:/usr/games:/usr/sbin/nologin
   man:x:6:12:man:/var/cache/man:/usr/sbin/nologin
   lp:x:7:7:lp:/var/spool/lpd:/usr/sbin/nologin
   mail:x:8:8:mail:/var/mail:/usr/sbin/nologin
   news:x:9:9:news:/var/spool/news:/usr/sbin/nologin
   uucp:x:10:10:uucp:/var/spool/uucp:/usr/sbin/nologin
   proxy:x:13:13:proxy:/bin:/usr/sbin/nologin
   www-data:x:33:33:www-data:/var/www:/usr/sbin/nologin
   backup:x:34:34:backup:/var/backups:/usr/sbin/nologin
   list:x:38:38:Mailing List Manager:/var/list:/usr/sbin/nologin
   irc:x:39:39:ircd:/var/run/ircd:/usr/sbin/nologin
   gnats:x:41:41:Gnats Bug-Reporting System (admin):/var/lib/gnats:/usr/sbin/nologin
   nobody:x:65534:65534:nobody:/nonexistent:/usr/sbin/nologin
   systemd-timesync:x:100:101:systemd Time Synchronization,,,:/run/systemd:/usr/sbin/nologin
   systemd-network:x:101:103:systemd Network Management,,,:/run/systemd:/usr/sbin/nologin
   systemd-resolve:x:102:104:systemd Resolver,,,:/run/systemd:/usr/sbin/nologin
   messagebus:x:103:106::/nonexistent:/usr/sbin/nologin
   syslog:x:104:110::/home/syslog:/usr/sbin/nologin
   _apt:x:105:65534::/nonexistent:/usr/sbin/nologin
   tss:x:106:111:TPM software stack,,,:/var/lib/tpm:/bin/false
   uuidd:x:107:114::/run/uuidd:/usr/sbin/nologin
   tcpdump:x:108:115::/nonexistent:/usr/sbin/nologin
   avahi-autoipd:x:109:117:Avahi autoip daemon,,,:/var/lib/avahi-autoipd:/usr/sbin/nologin
   usbmux:x:110:46:usbmux daemon,,,:/var/lib/usbmux:/usr/sbin/nologin
   rtkit:x:111:118:RealtimeKit,,,:/proc:/usr/sbin/nologin
   dnsmasq:x:112:65534:dnsmasq,,,:/var/lib/misc:/usr/sbin/nologin
   avahi:x:113:120:Avahi mDNS daemon,,,:/run/avahi-daemon:/usr/sbin/nologin
   cups-pk-helper:x:114:121:user for cups-pk-helper service,,,:/home/cups-pk-helper:/usr/sbin/nologin
   speech-dispatcher:x:115:29:Speech Dispatcher,,,:/run/speech-dispatcher:/bin/false
   kernoops:x:116:65534:Kernel Oops Tracking Daemon,,,:/:/usr/sbin/nologin
   saned:x:117:123::/var/lib/saned:/usr/sbin/nologin
   nm-openvpn:x:118:124:NetworkManager OpenVPN,,,:/var/lib/openvpn/chroot:/usr/sbin/nologin
   whoopsie:x:119:125::/nonexistent:/bin/false
   colord:x:120:126:colord colour management daemon,,,:/var/lib/colord:/usr/sbin/nologin
   sssd:x:121:127:SSSD system user,,,:/var/lib/sss:/usr/sbin/nologin
   geoclue:x:122:128::/var/lib/geoclue:/usr/sbin/nologin
   pulse:x:123:129:PulseAudio daemon,,,:/var/run/pulse:/usr/sbin/nologin
   hplip:x:124:7:HPLIP system user,,,:/run/hplip:/bin/false
   gnome-initial-setup:x:125:65534::/run/gnome-initial-setup/:/bin/false
   gdm:x:126:131:Gnome Display Manager:/var/lib/gdm3:/bin/false
   user:x:1000:1000:user,,,:/home/user:/bin/bash
   systemd-coredump:x:999:999:systemd Core Dumper:/:/usr/sbin/nologin
   shakir:x:1001:1000:shakir,,,:/home/shakir:/bin/bash

3. Check the current group memberships of a user.

   $ groups shakir
   shakir : user sudo finance

   First group in the list (user in this case) is the primary group for the user.

4. Update the primary group for a user, if necessary.

   $ sudo usermod -g finance shakir
   [sudo] password for user:

5. Remove the user from a specific group.

   $ sudo gpasswd -d shakir sudo
   Removing user shakir from group sudo

6. Verify the user's updated group memberships to confirm the changes.

   $ groups shakir
   shakir : finance user