Difference between adduser and usermod -G -a

adduser and usermod are two different utilities which have in common the fact that both can add a user to a group.

According to man adduser

adduser is friendlier front ends to the low level tools like useradd, groupadd and usermod programs.

More info:

• man adduser : adduser, addgroup - add a user or group to the system
• man usermod : usermod - modify a user account