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As explained in this article, we can use ssky-keygenand ssh-copy-idto log in to a remote Linux server without a password in 3 simple steps.

ssh-keygenCreate public and private keys. ssh-copy-idCopy the local host's public key to the remote host's authorized_keys file. ssh-copy-idAlso create a private key for the remote host's home ,/.ssh** and**/.ssh/authorized_keys** has appropriate permissions assigned.

This article also explains ssh-copy-id3 minor annoyances of using and how to use ssh-copy-idwith ssh-agent.

Step 1: Create public and private keys using ssh-key-gen on your local host

迹忆客@jiyik.com-local$ [Note: You are on jiyik.com-local here]

迹忆客@jiyik.com-local$ ssh-keygen
Generating public/private rsa key pair.
Enter file in which to save the key (/home/jiyik/.ssh/id_rsa):[Enter key]
Enter passphrase (empty for no passphrase): [Press enter key]
Enter same passphrase again: [Pess enter key]
Your identification has been saved in /home/jiyik/.ssh/id_rsa.
Your public key has been saved in /home/jiyik/.ssh/id_rsa.pub.
The key fingerprint is:
33:b3:fe:af:95:95:18:11:31:d5:de:96:2f:f2:35:f9 迹忆客@jiyik.com-local

Step 2: Copy the public key to the remote host using ssh-copy-id

迹忆客@jiyik.com-local$ ssh-copy-id -i ~/.ssh/id_rsa.pub jiyik.com-remote
迹忆客@jiyik.com-local's password:
Now try logging into the machine, with "ssh 'remote-host'", and check in:

.ssh/authorized_keys

to make sure we haven't added extra keys that you weren't expecting.

注意:ssh-copy-id Append the key to the remote host's .ssh/authorized_key .

Step 3: Log in to the remote host without entering a password

迹忆客@jiyik.com-local$ ssh jiyik.com-remote
Last login: Sun Nov 16 17:22:33 2008 from 192.168.1.2
[Note: SSH did not ask for password.]

迹忆客@jiyik.com-remote$ [Note: You are on remote-host here]

In most cases, the above 3 simple steps should get the job done.

We have also previously discussed in detail SSH and SCP from openSSH to openSSH without entering a password .

If you are using SSH2, we have previously discussed performing SSH and SCP without a password from SSH2 to SSH2 , from OpenSSH to SSH2 , and from SSH2 to OpenSSH .

Using ssh-copy-id with ssh-add/ssh-agent

If no value is passed for option -i and if ~/.ssh/identity.pub is not available, then ssh-copy-idthe following error message will be displayed.

迹忆客@jiyik.com-local$ ssh-copy-id -i jiyik.com-remote
/usr/bin/ssh-copy-id: ERROR: No identities found

If you have ssh-addloaded the key into using ssh-agent, ssh-copy-idwill fetch the key from to copy to the remote host. That is, when option -issh-agent is not passed to , it copies the key provided by the command to the remote host.ssh-copy-idssh-add -L

迹忆客@jiyik.com-local$ ssh-agent $SHELL

迹忆客@jiyik.com-local$ ssh-add -L
The agent has no identities.

迹忆客@jiyik.com-local$ ssh-add
Identity added: /home/jiyik/.ssh/id_rsa (/home/jiyik/.ssh/id_rsa)

迹忆客@jiyik.com-local$ ssh-add -L
ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAQEAsJIEILxftj8aSxMa3d8t6JvM79DyBV
aHrtPhTYpq7kIEMUNzApnyxsHpH1tQ/Ow== /home/jiyik/.ssh/id_rsa

迹忆客@jiyik.com-local$ ssh-copy-id -i jiyik.com-remote
迹忆客@jiyik.com-remote's password:
Now try logging into the machine, with "ssh 'jiyik.com-remote'", and check in:

.ssh/authorized_keys

to make sure we haven't added extra keys that you weren't expecting.
[Note: This has added the key displayed by ssh-add -L]

Three small troubles of ssh-copy-id

Here are some minor issues with ssh-copy-id.

• Default public key : ssh-copy-idUse ~/.ssh/identity.pub as the default public key file (i.e. when no value is passed to option -i ). Instead, I want it to use id_dsa.pub , id_rsa.pub , or identity.pub as the default key. i.e. if any of those exist, it should copy it to the remote host. If two or three exist, it should copy identity.pub by default .
• The agent has no identities : When ssh-agentis running and ssh-add -Lreturns " The agent has no identities " (i.e. no ssh-agentkeys were added to ), the authorized_keysssh-copy-id entry that sends the message "The agent has no identities" to the remote host will still be replicated .
• Duplicate entries in authorized_keys : I wish ssh-copy-idto verify duplicate entries on a remote host's authorized_keys. If executed multiple times on the local host ssh-copy-id, it will continue to append the same key on the remote host's authorized_keys file without checking for duplicates. Everything works as expected even with duplicate entries. However, I would like to keep my authorized_keys file cluttered.