Ygtjki

You could always do something like this:

scp ~/.ssh/id_rsa.pub user@remote.example.com:/tmp/id_rsa.pub
ssh user@remote.example.com 
cat /tmp/id_rsa.pub >> ~/.ssh/authorized_keys

I am not sure if you can cat from a local machine into an ssh session. Just move it to /tmp as suggested.

Edit: This is exactly what ssh-copy-id does. Just like Michael said.

This answer describes how to make the intended way shown in the question working.

You can execute a shell on the remote computer to interpret the special meaning of the >> redirection operator:

ssh tim@just.some.other.server sh -c "'cat >> .ssh/authorized_keys'" < /home/tim/.ssh/id_rsa.pub

The redirection operator >> is normally interpreted by a shell.

When you execute ssh host 'command >> file' then it is not guaranteed that command >> file will be interpreted by a shell. In your case command >> file is executed instead of the shell without special interpretation and >> was given to the command as an argument -- the same way as running command '>>' file in a shell.

Some versions of SSH (OpenSSH_5.9) will automatically invoke shell on the remote server and pass the command(s) to it when they detect tokens to be interpreted by a shell like ; > >> etc.

openssh does provide ssh-copy-id. The sequence would be:

• 
  

  Generate a decent 4k key

  
  
  

  ssh-keygen -t rsa -b 4096 -f ~/.ssh/id_rsa4k
  

  
  


• 
  

  Start your ssh-agent up and suck in information like SSH_AGENT_PID, etc.

  
  
  

  ssh-agent -s > ~/mysshagent
  source ~/mysshagent
  rm ~/mysshagent
  

  
  


• 
  

  Now start loading keys into your SSH Agent

  
  
  

  ssh-add ~/.ssh/id_rsa4k
  

  
  


• 
  

  Check that it is loaded

  
  
  

  ssh-add -l
  ssh-add -L
  

  
  
  

  This will show you what you have in the ssh-agent

  
  


• 
  

  Now actually SSH to a remote system

  
  
  

  ssh username@remotehost.network
  

  
  


• 
  

  Now you can run ssh-copy-id with no arguments:

  
  
  

  ssh-copy-id
  

  
  
  

  This creates ~/.ssh/authorized_keys and fills in the basic info required from ssh-agent.

  
  

I had troubles with ssh-copy-id when choosing another port than 22...
so here is my oneliner with a different ssh-port (e.g. 7572):

ssh yourServer.dom -p7572 "mkdir .ssh; chmod 700 .ssh; umask 177; sh -c 'cat >> .ssh/authorized_keys'" < .ssh/id_rsa.pub

Indeed the the ssh-copy-id command does exactly this (from the openssh-client package):

ssh-copy-id user@host

Note:
host means IP address or domain.

I would like also to add some additional information to this

1) We can specify a different port for SSH on destination server:

ssh-copy-id "-p 8127 user@host"

Note:
The port must be in front of the user@host or it will not resolve.

Source

2) We can specify a file with a public key:

ssh-copy-id -i ~/.ssh/id_rsa.pub user@host

Note:
The -i option allows us to indicate the appropriate location of the name with the file that contains the public key.

Sometimes it can come in handy, especially if we store it in a non-standard location or we have more than one public key on our computer and we want to point to a specific one.