/etc/group is a text file which defines the groups to which users belong under Linux and UNIX operating system. Under Unix / Linux multiple users can be categorized into groups. Unix file system permissions are organized into three classes, user, group, and others.
Here is example of /etc/group file:
root:x:0: daemon:x:1: bin:x:2: sys:x:3: adm:x:4:username 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:username fax:x:21: voice:x:22: cdrom:x:24:username, username1 floppy:x:25: tape:x:26: sudo:x:27: audio:x:29:pulse dip:x:30: www-data:x:33:username 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:username staff:x:50: games:x:60: users:x:100: nogroup:x:65534: libuuid:x:101: crontab:x:102: syslog:x:103:
|Group||:||Password||:||Group ID (GID)||:||Group List|
Group: It is the name of group. If you run ls -l command, you will see this name printed in the group field.
Password: Generally password is not used, hence it is empty/blank. It can store encrypted password. This is useful to implement privileged groups.
Group ID (GID): Each user must be assigned a group ID. You can see this number in your / etc/ passwd file.
Group List: It is a list of user names of users who are members of the group. The user names, must be separated by commas.
To view in which group user belongs; type
Reade more about command groups.