mktemp: failed to create file via template '/root/.ssh/ssh-copy-id_id.XXXXXXXXXX': Permission denied

Hello,

I have followed this tutorial on Raspbian Jessie Lite, but when I try to copy the public key to the server server1.example.com I get this error:

rdiff-backup@backup:/backup$ ssh-copy-id -i .ssh/id_rsa.pub [email protected] -p2290
The authenticity of host '[example.com]:2290 ([88.58.54.131]:2290)' can't be established.
ECDSA key fingerprint is 42:1n:78:4d:ef:31:g6:h1:a0:6b:54:e5:85:83:19:89.
Are you sure you want to continue connecting (yes/no)? yes
mktemp: failed to create file via template ‘/root/.ssh/ssh-copy-id_id.XXXXXXXXXX’: Permission denied
mktemp failed

This the content of my .ssh/config file
host web_server
hostname server1.example.com
user ssh_user
identityfile /backup/.ssh/id_rsa
compression yes
cipher blowfish
protocol 2

Best regards

 

I used cat to copy the public key in the remote file but finally I used attic.

Best regards