user account maintanance
1) How to add user
# useradd singa
2) How to change passwd
# passwd singa
3) If you need to changes user account
# vi /etc/passwd
4) Let’s say you have NIS server, then you need to change NIS account/passwd
# vi /var/yp/nis/passwd
# vi /var/yp/nis/shadow
# passwd -r nis singa
# vi /var/yp/nis/shadow
# passwd -r nis singa
