ssh login without password

http://www.linuxproblem.org/art_9.html

e.g. from id_a@server_a, login without password to id_b@server_b_1 ~ id_b@server_b_10

[id_a@server_a]$ for host in server_b_{1..10};do cat ~/.ssh/id_rsa.pub | ssh id_b@$host 'cat >> .ssh/authorized_keys'; done
id_b@server_b_1's password:

id_b@server_b_2's password:
...

id_b@server_b_10's password: