gistfile1.sh

# How to add user into group, and make changes take effect *without logout/login*: the *newgrp* command 
#
# Do note that this method will only update the groups, in the current shell session (and its child-processes).
# New shell sessions will not have the groups updated - either use this method to update the groups in each shell 
# session, or logout/login to make the group update permanent by default 
#
# In short: 
#     $ sudo adduser user_x my_grp
#     $ newgrp my_grp && newgrp
# 
# Here is the rundown annotated:

#Add user_x into group sambashare
user_x@stest:~$ sudo adduser user_x sambashare
user_x@stest:~$ id
uid=1001(user_x) gid=1002(user_x) groups=1002(user_x),20(dialout)
  #changes did not take effect

user_x@stest:~$ newgrp 
user_x@stest:~$ id
uid=1001(user_x) gid=1002(user_x) groups=1002(user_x),20(dialout)
  #changes still did not take effect

user_x@stest:~$ newgrp sambashare
user_x@stest:~$ id
uid=1001(user_x) gid=115(sambashare) groups=1002(user_x),20(dialout),115(sambashare)
  #changes *did* take effect now:
  #   - changed 'gid=115(sambashare)'
  #   - appended '115(sambashare)'

user_x@stest:~$ newgrp 
user_x@stest:~$ id
uid=1001(user_x) gid=1002(user_x) groups=1002(user_x),20(dialout),115(sambashare)
  #reestablished 'gid=1002(user_x)'
  # all done now