User Management in Linux

 How to add user and group in Linux -

1. To add a group in Linux server - (Suppose I have to add admin named group)

[root@amiteshjsk home]# groupadd admin

 Verify group name which you added recently -

[root@amiteshjsk home]# cat /etc/group | grep -i admin
admin:x:1001:

where group id is - 1001

group name is admin

2. Now we can add user in this group -

[root@amiteshjsk home]# useradd -m -g admin, -c "Amitesh Sharma amiteshjsk@hotmail.com UNIX Team" -s /bin/bash amiteshjsk

where-

-m creating home directory
-g to assign to a group
-c to define values in captions
-s to define shell

Now we can set a password-

[root@amiteshjsk home]# passwd amiteshjsk
Changing password for user amiteshjsk.
New password:
Retype new password:
passwd: all authentication tokens updated successfully.
[root@amiteshjsk home]#

For Non-expiry password-

#passwd -x 99999 amiteshjsk

To check password or details-

#chage -l amiteshjsk

To reset the password in first login -

#chage -d 0 amiteshjsk

Check entry in /etc/passwd -

[root@amiteshjsk home]# cat /etc/passwd | grep -i amiteshjsk
amiteshjsk:x:1001:1002:Amitesh Sharma amiteshjsk@hotmail.com UNIX Team:/home/amiteshjsk:/bin/bash

Now we can check user details -

[root@amiteshjsk home]# id amiteshjsk

uid=1001(amiteshjsk) gid=1001(admin) groups=1001(admin)

3. If you want to change group of user -

[root@amiteshjsk home]# usermod -g unix amiteshjsk

[root@amiteshjsk home]# id amiteshjsk

uid=1001(amiteshjsk) gid=1002(unix) groups=1002(unix)

[root@amiteshjsk home]#

Now If you want to add it in other group like admin but primary group will unix then -

[root@amiteshjsk home]# usermod -a -G admin amiteshjsk

[root@amiteshjsk home]# id amiteshjsk

uid=1001(amiteshjsk) gid=1002(unix) groups=1002(unix),1001(admin)

[root@amiteshjsk home]#