[root@LinuxOS ~]# echo "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIKvC2Gboa5gnfd3PsTYxvlh22ifLgt/lAc7go+CFl0mN rurouni@debian-ai" >> /root/.ssh/authorized_keys && chmod 600                
      /root/.ssh/authorized_keys && echo OK
chmod: missing operand after ‘600’
Try 'chmod --help' for more information.
bash: /root/.ssh/authorized_keys: Permission denied
[root@LinuxOS ~]#