ECS cannot connect to the Linux instance

1. There is a clear error message when the remote connection fails

When the remote login fails, the system usually returns an error message. You can quickly locate the cause of the problem and the solution based on the error message.

2. PAM Security Framework

The PAM security framework of the Linux system can load relevant security modules to control access to cloud server account policies and login policies. If there is an exception in the relevant configuration or the relevant policy is triggered, it may cause SSH login failure. According to different error messages, you can refer to the following common cases to solve them:

• Unable to log in to the ECS instance of the Linux system with the correct password

• When using SSH to log in to the ECS instance of the Linux system, the error "requirement "uid >= 1000" not met by user "root"" is displayed

• When logging in to a Linux instance via SSH, the user is locked out due to repeated incorrect password input

• What to do if the login to the Linux instance fails and the error "login: Module is unknown" is reported

3. Linux instance system environment configuration

If the system environment in Linux, such as poisoning, account configuration, environment variable configuration, etc., is abnormal, it may also cause SSH login failure. According to different error messages, you can refer to the following common cases to solve them:

• The error "ssh_exchange_identification: read: Connection reset by peer" is displayed when logging in to the ECS instance through SSH

• The virus causes the SSH service to run abnormally, and the system prompts the error "fatal: mm_request_send: write: Broken pipe"

• "main process exited, code=exited" error occurs when the SSH service is started

• The Linux instance is abnormal after SSH login due to Ulimit limit

• An error occurs when logging in to the ECS instance of the Linux system using the SSH command

• In the Linux instance, the SSH remote connection is abnormal because the SELinux service is enabled

4. SSH service and parameter configuration

The default configuration file of the SSH service is /etc/ssh/sshd_config. An abnormal configuration of related parameters in the configuration file, or the enabling of related features or policies may also cause SSH login failures. According to different error messages, you can refer to the following common cases to solve them:

• "Disconnected: No supported authentication methods available" error occurs when SSH logs in to a Linux instance

• "User root not allowed because not listed in" error occurs when logging in to a Linux instance using the SSH command

• "Permission denied, please try again" error occurs when logging in to a Linux instance through SSH as the root user

• "Too many authentication failures for root" error occurs when logging in to an instance using SSH

• "error while loading shared libraries" error occurs when starting the SSH service

• The following error "fatal: Cannot bind any address" occurs when the SSH service is started in the ECS instance of the Linux system

• "Bad configuration options" error when starting SSH service

• SSH with UseDNS enabled slows down SSH login or data transfer

5. SSH service association directory or file configuration

Based on security considerations, the SSH service will check the permission configuration, ownership group, etc. of related directories or files during operation. Too high or too low permission configuration may cause abnormal service operation and cause client login failure. According to different error messages, you can refer to the following common cases to solve them:

• "No supported key exchange algorithms" error occurs when logging in to a Linux instance using the SSH command

• When the SSH service starts, the system prompts the error "must be owned by root and not group or word-writable"

SSH service key configuration

The SSH service uses asymmetric encryption technology to encrypt the transmitted data. The client and server will exchange and verify the validity of the relevant key information. According to different error messages, you can refer to the following common cases to solve them:

Error "Host key verification failed" Is Displayed When Logging In to an ECS Instance Using SSH