Add a user without using 'adduser' command

I wanna add a user directly manipulating the file 'passwd', not using 'adduser' command.

So I did like this:

# echo "$name $uid $gid $......"
# mkdir $homedir

But when I try to give $name a password:

# passwd $name

Shell said 'Authentication token manipulation error'

Now what am I supposed to do now?

..

I think it will be so kind if you let me know exactly what procedure I have take to add a new user not using 'adduser' command.

..

Please help me out, guys.

And I'd like to appreciate for the previous help.