ssh-keygen -lf ~/ssh/rsa_key.pub
2048 d5:cu:15:df:5d:44:…

vi ~/.ssh/config

Host *
  USER root
  AddKeysToAgent yes
  TcpKeepAlive yes
  ServerAliveInterval 60
  ServerAliveCountMax 60

If file and folder permissions are fine but you still have this error:
chown -R root.root /root/


sudo dnf install putty
puttygen ~/Downloads/id_rsa.ppk -O private-openssh -o id_rsa.key
chmod 600 id_rsa.key


A small memory footprint suitable for memory-constrained environments – Dropbear can compile to a 110kB statically linked binary with uClibc on x86 (only minimal options selected)
Dropbear server implements X11 forwarding, and authentication-agent forwarding for OpenSSH clients
Can run from inetd or standalone
Compatible with OpenSSH ~/.ssh/authorized_keys public key authentication
The server, client, keygen, and key converter can be compiled into a single binary (like busybox)
Features can easily be disabled when compiling to save space
Multi-hop mode uses SSH TCP forwarding to tunnel through multiple SSH hosts in a single command. dbclient user1@hop1,user2@hop2,destination

mv ~/.ssh/ssh-agent.localhost.localdomain.sock{,_backup}

Then you can relogin to your account and ssh-add work again. It could happen after system crash.

echo ‘Your text’ | ssh root@server “cat >> /tmp/some_file”