Linux Administration ( part 2 ): creating/managing groups in Linux
What are Groups:
Groups in Linux are used to manage users and provide them a set of privileged permissions for reading, writing, and executing. by default Linux already has some groups such as sudo cdrom floppy audio dip video plugdev netdev bluetooth lpadmin scanner
Checking all groups of which a user is a member
we can use the following commands to do this:
$ groups username
/etc/group
This particular file contains information regarding different groups and their members, and each line is written in the following format:
GROUP_NAME:x(WHICH_REPRESENT_PASSWORD_WHICH_IS_NULL):GROUP_ID:LIST_OF_ALL_GROUP_USERS_SEPARATED_BY_COMMA
or
GROUP_NAME:x(WHICH_REPRESENT_PASSWORD_WHICH_IS_NULL):GROUP_ID:ONE_USER_AND_FOR_OTHER_MEMBERS_OF_GROUP_SEPARATE_LINES_ARE_THERE
Creating new group
To create a group we can use groupadd command
$ groupadd [option] group_name
this command creates a new group with the name group_name, and also add its entry to /etc/group and /etc/gshadow
-> /etc/login.defs
whenever a new group is created, some of the default values are taken from this file
[options]
- g integer ## to set specific GID
- -K GID_MIN=1200 -K GID_MAX=1500 ## changing some default values from /etc/login.defs
- -r ## use this to create a system group
$ groupadd -g 1005 grouptest
Creating a testuser
Adding user to group
adding user testuser to group grouptest
$ usermod -aG GROUP_NAME USER_NAME
$ usermod -aG grouptest testuser
Removing user from group
$ gpasswd -d USER_NAME GROUP_NAME
$ gpasswd -d testuser grouptest
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