userauth_pubkey: signature algorithm ssh-rsa not in PubkeyAcceptedAlgorithms

Overview: This article provides steps to troubleshoot and resolve the "userauth_pubkey: signature algorithm ssh-rsa not in PubkeyAcceptedAlgorithms" error, enable ssh-rsa authentication, and view available key types and key exchange algorithms on a Linux server.

Step 1. Login to server and tail /var/log/secure to check errors. Refer below example.

root@gateway ~]# tail -f /var/log/secure

userauth_pubkey: signature algorithm ssh-rsa not in PubkeyAcceptedAlgorithms

Step 2. Find which key type is used in the server by running the below command.

root@gateway ~]# ssh-keygen -l -f /usr/local/etc/ezlogin/id_key.pub
4096 SHA256:n4lmX53/gwkKB4+nSQ30hZXxXK+DRG1LPc7N1KN/1Ag ezlogin (RSA)

In the above example, the RSA key type is used.

Step 3. Run the following command to see which all key types are enabled on the server.

root@gateway ~]# sshd -T | grep -i key

pubkeyacceptedalgorithms [email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],ssh-ed25519,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,[email protected],[email protected],rsa-sha2-512,rsa-sha2-256

Step 4. Open /etc/ssh/sshd_config and append the below line to enable ssh-rsa.

root@gateway ~]# vim /etc/ssh/sshd_config

PubkeyAcceptedKeyTypes +ssh-rsa

root@gateway ~]# systemctl restart sshd

Step 5. Re-run the below command and confirm that ssh-rsa has been enabled.

root@gateway ~]# sshd -T | grep -i key

Step 6. Try to modify the user now and confirm it's working fine.

How to view the list of KEX and Keys in the Linux server?

How to list keys in the Linux server?

root@linux ~]# ssh -Q key

ssh-ed25519
[email protected]
ssh-rsa
ssh-dss
ecdsa-sha2-nistp256
ecdsa-sha2-nistp384
ecdsa-sha2-nistp521
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]

How to list KEX in the Linux server?

root@linux ~]# ssh -Q kex

diffie-hellman-group1-sha1
diffie-hellman-group14-sha1
diffie-hellman-group14-sha256
diffie-hellman-group16-sha512
diffie-hellman-group18-sha512
diffie-hellman-group-exchange-sha1
diffie-hellman-group-exchange-sha256
ecdh-sha2-nistp256
ecdh-sha2-nistp384
ecdh-sha2-nistp521
curve25519-sha256
[email protected]

Related Articles:

Error: User modify failed. Cannot modify user on this node: Authentication by SSH key failed!

Error: User modify failed. Cannot modify user on other node: Authentication by SSH key failed!