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Linux SSH Failure: "Connection closed by remote host" or "no hostkey alg"

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Last updated: 2024-01-06 17:32:18

Issue Description

During login to a Linux instance via SSH key, "ssh_exchange_identification: Connection closed by remote host" or "no hostkey alg" is displayed.

Common Causes

sshd configuration file permissions, such as the permissions of the /var/empty/sshd or /etc/ssh/ssh_host_rsa_key configuration file, are modified, which may cause a failure in login via SSH key.

Solution

Perform the steps based on the actual error message to modify the configuration file permissions:
If the error message is "ssh_exchange_identification: Connection closed by remote host", see Modifying permissions of /var/empty/sshd file.
If the error message is "no hostkey alg", see Modifying permissions of /etc/ssh/ssh_host_rsa_key file.

Troubleshooting Procedure

Modifying permissions of /var/empty/sshd file

2. Run the following command to view the error cause:
sshd -t
Information similar to the following is returned:
"/var/empty/sshd must be owned by root and not group or world-writable."
3. Run the following command to modify the permissions of the /var/empty/sshd/ file:
chmod 711 /var/empty/sshd/

Modifying permissions of /etc/ssh/ssh_host_rsa_key file

2. Run the following command to view the error cause:
sshd -t
The returned information contains the following field:
"/etc/ssh/ssh_host_rsa_key are too open"
3. Run the following command to modify the permissions of the /etc/ssh/ssh_host_rsa_key file:
chmod 600 /etc/ssh/ssh_host_rsa_key
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