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.
$ sudo groupadd finance [sudo] password for user:
$ 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
$ 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:
$ sudo usermod -g finance shakir
$ sudo usermod -a -G sudo shakir
$ sudo usermod -a -G sudo,user shakir
$ groups shakir shakir : finance sudo user
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