How to add existing users in existing groups in linux and see which user is in which group

Add to group:

[root@288832-web3 ~]# usermod -a -G group1 user1
[root@288832-web3 ~]# usermod -a -G group2 user2

View which group which user belongs:
[root@288832-web3 ~]# groups user1
user1 : user1 apache group1

[root@288832-web3 ~]# groups user2
user2 : user2 apache group2

Add a new user to SVN for UKSS

Login as root via SSH on UKSS

Here we are adding a new user with the username: user1

Add new user: useradd user1

Add Password for the new user: passwd user1

Add user to groups: 

gpasswd -a user1 svn

gpasswd -a user1 apache