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 inaccessible.

Related: How to remove user from groups in Linux

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

Steps to add user to group in Linux:

  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