Ubuntu SSH Algorithm negotiation failed

Ubuntu SSH Algorithm negotiation failed

Situation

Server responded"Algorithm negotiation failed"
Key exchange with the remote host failed. This can happen for
example computer does not support the selected  
algorthms. 

When ssh to a ubuntu system,putty can connect but ‘SSH Secure Shell Client’ is failed,according to the pop-up error message we can know that
the algorithm negotiation failed, after searching high-and-low for this fix, I finally found it’s fix…

Reason

Because i had past updated server, it’s that means i had updated the sshd algorithm negotiation on server meanwhile, but the sshd algorithm negotiation in client is the old, so server cannot compatible the algorithm negotiation from client.

The Way to resolve

  1. Use a different system or the console to drop to a shell. Such as Putty
  2. Chmod 777 & Edit the “/etc/ssh/sshd_config” file
  3. Add all of the algorithm negotiation to sshd_config
  4. Restart sshd sevice
    Add following code to sshd_config
Ciphers aes128-cbc,aes192-cbc,aes256-cbc,aes128-ctr,aes192-ctr,aes256-ctr,3des-cbc,arcfour128,arcfour256,arcfour,blowfish-cbc,cast128-cbc

MACs hmac-md5,hmac-sha1,umac-64@openssh.com,hmac-ripemd160,hmac-sha1-96,hmac-md5-96

KexAlgorithms diffie-hellman-group1-sha1,diffie-hellman-group14-sha1,diffie-hellman-group-exchange-sha1,diffie-hellman-group-exchange-sha256,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group1-sha1,curve25519-sha256@libssh.org
root@ubuntu:/home/app# chmod 777 /etc/ssh/sshd_config
root@ubuntu:/home/app# vi /etc/ssh/sshd_config
root@ubuntu:/home/app# service sshd restart

Finally

Congratulations! you have success resolved Algorithm negotiation failed


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