How to add user to group in Linux

Group is a way to organize users in Linux where each user needs to be assigned a primary group. Users can also be a member of multiple other groups.

System permissions and privileges can be assigned to both user and group where members of a group will inherit the group's privileges.

Local users and groups can be configured manually by editing /etc/passwd and /etc/group files, but a misconfiguration could easily cause the whole system to be inaccessible.

Therefore, adding users to groups using dedicated tools such as usermod would simplify the process while minimizing the risk.

1. Launch terminal.
2. Create a new group if required.

   $ sudo groupadd finance
   [sudo] password for user:

3. Get the list of users for 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:1001:1002:shakir,,,:/home/shakir:/bin/bash

4. Get the list of groups for your system.

   $ getent group 
   root:x:0:
   daemon:x:1:
   bin:x:2:
   sys:x:3:
   adm:x:4:syslog,user
   tty:x:5:
   disk:x:6:
   lp:x:7:
   mail:x:8:
   news:x:9:
   uucp:x:10:
   man:x:12:
   proxy:x:13:
   kmem:x:15:
   dialout:x:20:
   fax:x:21:
   voice:x:22:
   cdrom:x:24:user
   floppy:x:25:
   tape:x:26:
   sudo:x:27:user
   audio:x:29:pulse
   dip:x:30:user
   www-data:x:33:
   backup:x:34:
   operator:x:37:
   list:x:38:
   irc:x:39:
   src:x:40:
   gnats:x:41:
   shadow:x:42:
   utmp:x:43:
   video:x:44:
   sasl:x:45:
   plugdev:x:46:user
   staff:x:50:
   games:x:60:
   users:x:100:
   nogroup:x:65534:
   systemd-timesync:x:101:
   systemd-journal:x:102:
   systemd-network:x:103:
   systemd-resolve:x:104:
   crontab:x:105:
   messagebus:x:106:
   input:x:107:
   kvm:x:108:
   render:x:109:
   syslog:x:110:
   tss:x:111:
   bluetooth:x:112:
   ssl-cert:x:113:
   uuidd:x:114:
   tcpdump:x:115:
   ssh:x:116:
   avahi-autoipd:x:117:
   rtkit:x:118:
   netdev:x:119:
   avahi:x:120:
   lpadmin:x:121:user
   scanner:x:122:saned
   saned:x:123:
   nm-openvpn:x:124:
   whoopsie:x:125:
   colord:x:126:
   sssd:x:127:
   geoclue:x:128:
   pulse:x:129:
   pulse-access:x:130:
   gdm:x:131:
   lxd:x:132:user
   user:x:1000:
   sambashare:x:133:user
   systemd-coredump:x:999:
   finance:x:1001:
   shakir:x:1002:

5. Change primary group for a user.

   $ sudo usermod -g finance shakir

6. Add existing user secondary groups.

   $ sudo usermod -a -G sudo shakir

7. Add an existing user to multiple groups.

   $ sudo usermod -a -G sudo,user shakir

8. View the groups that a user is assigned to.

   $ groups shakir
   shakir : finance sudo user