Editing Linux 101 hacks (section)

=='''Hack 73. Use ssh-copy-id along with ssh-agent'''==


'''Using ssh-copy-id along with the ssh-add/ssh-agent'''


When no value is passed for the option -i and If ~/.ssh/identity.pub is not available, ssh-copy-id will display the following error message.


jsmith@local-host$ ssh-copy-id -i remote-host


/usr/bin/ssh-copy-id: ERROR: No identities found


If you have loaded keys to the ssh-agent using the ssh-add, then ssh-copy-id will get the keys from the ssh-agent to copy to the remote-host. i.e, it copies the keys provided by ssh-add -L command to the remote-host, when you don’t pass option -i to the ssh-copy-id.


jsmith@local-host$ ssh-agent $SHELL


jsmith@local-host$ ssh-add -L The agent has no identities.


jsmith@local-host$ ssh-add


Identity added: /home/jsmith/.ssh/id_rsa (/home/jsmith/.ssh/id_rsa)


jsmith@local-host$ ssh-add -L ssh-rsa


AAAAB3NzaC1yc2EAAAABIwAAAQEAsJIEILxftj8aSxMa3d8t6JvM79D aHrtPhTYpq7kIEMUNzApnyxsHpH1tQ/Ow== /home/jsmith/.ssh/id_rsa


jsmith@local-host$ ssh-copy-id -i remote-host jsmith@remote-host’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. <nowiki>[</nowiki>'''Note''': This has added the key displayed by ssh-add -L]

'''Three Minor Annoyances of ssh-copy-id'''


Following are few minor annoyances of the ssh-copy-id.


# Default public key: ssh-copy-id uses ~/.ssh/identity.pub as the default public key file (i.e when no value is passed to option -i). Instead, I wish it uses id_dsa.pub, or id_rsa.pub, or identity.pub as default keys. i.e If any one of them exist, it should copy that to the remote-host. If two or three of them exist, it should copy identity.pub as default. 

# The agent has no identities: When the ssh-agent is running and the ssh-add -L returns “The agent has no identities” (i.e no keys are added to the ssh-agent), the ssh-copy-id will still copy the message “The agent has no identities” to the remote-host’s authorized_keys entry. 

# Duplicate entry in authorized_keys: I wish ssh-copy-id validates duplicate entry on the remote-host’s authorized_keys. If you execute ssh-copy-id multiple times on the local-host, it will keep appending the same key on the remote-host’s authorized_keys file without checking for duplicates. Even with duplicate entries everything works as expected. But, I would like to have my authorized_keys file clutter free.