Linux User Group permissions
Welcome to our tutorial Linux group permissions . we have already discussed user permissions in tutorial introduction to linux user permissions. In this tutorial we will use basic commands like
In linux if need to assign permissions to group of specific users to directory you have option to create a group in linux. Put all these users into this group
and then assign permission to that directory at group level instead of individual user. It will be more clear when we use practicle examples.
There are two ways to use group permissions in Linux . GUI tools and command sin CLI mode. GUI tools are available in different distribution of linux new users can use
these GUI tools to grasp concept of group and user permission in linux. People who are comfortable and advanced user can use CLI commands.In this tutorial we will use basic commands like groupadd, groupmod, usermod, groupdel,groups and will also briefly talk about /etc/group file
In this tutorial we will discuss commands
groupadd
To add group to system use command groupadd
Syntax : groupadd groupname
example groupadd teamA
Above command will create a group called teamA
see below example commands
[root@shahid ~]# groupadd development [root@shahid ~]# groupadd testers [root@shahid ~]# groupadd sales [root@shahid ~]# groupadd marketing [root@shahid ~]# groupadd support
We have added five groups
development
testers
sales
marketing
Support
/etc/group
To view group permission you can view file /etc/group
[root@shahid ~]# [root@shahid ~]# cat /etc/group | tail stapusr:x:156: stapsys:x:157: stapdev:x:158: tcpdump:x:72: shahid:x:1000:shahid development:x:1001: testers:x:1002: sales:x:1003: marketing:x:1004: support:x:1005: [root@shahid ~]#
user can be a part of more than one group
first field in file is used for group’s name. Second field is for password and can be empty third field is for group identification (GID). Fourth field is for list of
members in group. In our case we just created groups and have not assigned any user yet so there is nothing
usermod
I have quickly created few new users using useradd command
[root@shahid ~]# useradd john [root@shahid ~]# useradd michael [root@shahid ~]# useradd alex [root@shahid ~]# useradd khalid [root@shahid ~]# useradd david [root@shahid ~]# useradd rob [root@shahid ~]# useradd tim
Now I am going to assign them to different groups
[root@shahid ~]# usermod -a -G development john [root@shahid ~]# usermod -a -G testers michael [root@shahid ~]# usermod -a -G sales alex [root@shahid ~]# usermod -a -G marketing alex [root@shahid ~]# usermod -a -G marketing khalid [root@shahid ~]# usermod -a -G support rob [root@shahid ~]# usermod -a -G support tim
Kool we have added users to group. We used switch -a which means append. If you dont use this switch user will be removed from all previously assigned group and will
be added to new group. Switch -G is group to which you are assigning user. As we mentioned we can and have assigned alex to multiple groups sales and marketing
groupmod
You can change name of group by using command groupmod
group [root@shahid ~]# groupmod -n dev development [root@shahid ~]# cat /etc/group | tail marketing:x:1004:alex,khalid support:x:1005:rob,tim john:x:1006: michael:x:1007: alex:x:1008: khalid:x:1009: david:x:1010: rob:x:1011: tim:x:1012: dev:x:1001:john [root@shahid ~]#
groupdel
To delete group permanently you can use command groupdel
[root@shahid ~]# groupdel dev [root@shahid ~]# cat /etc/group | tail sales:x:1003:alex marketing:x:1004:alex,khalid support:x:1005:rob,tim john:x:1006: michael:x:1007: alex:x:1008: khalid:x:1009: david:x:1010: rob:x:1011: tim:x:1012: [root@shahid ~]#
groups
if user wants to see list of groups to which user belongs can type command groups
I will switch to my user shahid and will see my userid shahid belongs to which group
[root@shahid ~]# su - shahid Last login: Fri Feb 19 11:46:05 GMT 2016 from 192.168.156.33 on pts/0 [shahid@shahid ~]$ groups shahid wheel [shahid@shahid ~]$
I can see my userid belongs to two groups shahid(default group) and wheel
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