# Linux - ssh without password

###### tags: `linux` `ssh`

# Manual Steps
1. create a key pair
ssh-keygen -t rsa -N ""
2. copy ~/.ssh/id_rsa.pub to remote host ~/.ssh/authorized_keys
3. modify /etc/ssh/sshd_config, remove comment of the lines below
RSAAuthentication yes
PubkeyAuthentication yes
AuthorizedKeysFile .ssh/authorized_keys
4. restart sshd and done
service sshd restart

!!! you may choose other encryption method. Modify step 1 and step 2:
ssh-keygen -t dsa -N ""
copy ~/.ssh/id_dsa.pub to host ~/.ssh/authorized_keys
!!! for old ssh can only RSA version 1. Modify step 1 and step 2:
ssh-keygen -t rsa1 -N ""
copy ~/.ssh/identity.pub to host ~/.ssh/authorized_keys
!!! you can use 'ssh-copy-id' to copy public key to authorized_keys in remote host
(1) ssh-keygen
root@node01:~# ssh-keygen
Generating public/private rsa key pair.
Enter file in which to save the key (/root/.ssh/id_rsa): 
Enter passphrase (empty for no passphrase): 
Enter same passphrase again: 
Your identification has been saved in /root/.ssh/id_rsa.
Your public key has been saved in /root/.ssh/id_rsa.pub.
The key fingerprint is:
33:f3:0b:2a:bf:98:78:fd:ee:30:01:b8:22:e1:f3:f6 root@node01
The key's randomart image is:
+--[ RSA 2048]----+
|                 |
|   .             |
|. . .            |
|.. . .           |
|oo.   . S        |
|..o    . =       |
|   o .o . .      |
|  ..+o.+ . .     |
|  ..oE+=+ .      |
+-----------------+

(2) ssh-copy-id
root@node01:~# ssh-copy-id root@node02
The authenticity of host 'node02 (10.10.10.2)' can't be established.
ECDSA key fingerprint is 42:59:d8:46:55:d5:51:7e:24:fc:7d:72:9b:1f:45:73.
Are you sure you want to continue connecting (yes/no)? yes
/usr/bin/ssh-copy-id: INFO: attempting to log in with the new key(s), to filter out any that are already installed
/usr/bin/ssh-copy-id: INFO: 1 key(s) remain to be installed -- if you are prompted now it is to install the new keys
root@node02's password: 

Number of key(s) added: 1

Now try logging into the machine, with:   "ssh 'root@node02'"
and check to make sure that only the key(s) you wanted were added.
root@node01:~#
!!! Add fingerprint of a server to your know_hosts file so that ssh will automatically accept keys to login remote server without asking yes/no.
root@admin:~# ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default 
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether 52:54:00:d5:6e:64 brd ff:ff:ff:ff:ff:ff
    inet 192.168.124.100/24 brd 192.168.124.255 scope global eth0
       valid_lft forever preferred_lft forever
    inet6 fe80::5054:ff:fed5:6e64/64 scope link 
       valid_lft forever preferred_lft forever
root@admin:~# ssh-keyscan -H 192.168.124.101 >> ~/.ssh/known_hosts
# 192.168.124.101 SSH-2.0-OpenSSH_6.6.1p1 Ubuntu-2ubuntu2
# 192.168.124.101 SSH-2.0-OpenSSH_6.6.1p1 Ubuntu-2ubuntu2
root@admin:~# cat ~/.ssh/known_hosts 
|1|3NrXKx8Sne+syaWT4nP1iGmfDqY=|OKNyHXHhcRPzbWw5uULQTqE1aHw= ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBFpANWJQkv9YwkL5bghbxndmBi3YnXOq3HdGFVtTY2WCLfxlyyj0CWb2nR7XNu2eYus+xiNEKAc3HSFw+wj2we4=
|1|tO1VmVo7f5aPqJf+WZbs904WIYA=|J9rN6jdVrvhTzajKSaFa4YJq79Y= ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQDlmHHgsyjY0E/RvBA2dg9t51T5jiF/rgVFwDsq/NBpym4zfLj4eLqmKnmpLFvdSOssyz5yIj0sqUQj9ilTuM3HlENAy6zISIm+rXiPgP4tt6PUBXYjauYbXeJfrVUorDnnS5Q62eCoL4VZQpqoOpsrmPvuOHv8DZ977TTwXcsJcgvlPufoPbxQxL+71fmltuP7FZzt8rPPHl7z4t5oNCjPAr3p+H/DQH9XOtizoUeYcTo7lZvgDZzCvhRD+MrYk/xZ8+6h5c48UUL8pFKD839J0cksZiN9Kfch6rU3+kk0ELKasTAq1FzTUr5Ir4bWGAzQyCiCHBrDbSgt+/udm0+L
root@admin:~# ssh 192.168.124.101
Welcome to Ubuntu 14.04.3 LTS (GNU/Linux 3.19.0-25-generic x86_64)

 * Documentation:  https://help.ubuntu.com/

  System information as of Tue Mar  1 22:44:03 CST 2016

  System load:  0.0               Processes:           74
  Usage of /:   38.7% of 2.89GB   Users logged in:     1
  Memory usage: 5%                IP address for eth0: 192.168.124.101
  Swap usage:   0%

  Graph this data and manage this system at:
    https://landscape.canonical.com/

118 packages can be updated.
51 updates are security updates.

Last login: Tue Mar  1 22:44:03 2016 from 192.168.124.100
root@mon01:~#