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    Linux Instance Login Failures

    Last updated: 2024-01-06 17:32:18
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      This document describes possible causes of Linux instance login failures and troubleshooting methods, helping you detect, locate and resolve problems.

      Troubleshooting the Issue

      Using the Diagnosis Tool

      Tencent Cloud provides a diagnosis tool to help you determine whether the problem is due to common bandwidth, firewall, or security group configurations issues. More than 70% of the problems can be located by this tool. You can locate problems that result in login failures based on the detected causes.
      1. Click Self-diagnose to open the self-diagnosis tool.
      2. Select the target CVM instance as prompted and click Start Detection.

      Using TAT to send commands

      You can use TAT to send commands to an instance for troubleshooting and problem locating. The directions are as follows:
      1. Log in to the CVM console and click the target instance ID in the instance list.
      2. On the instance details page, select the Run Commands tab and click Execute command.
      3. In the Execute command pop-up window, select a command as needed. Click Execute command and view the result. For example, enter df -TH and click Execute command to view the result of an instance without logging in to it. For more information, see TencentCloud Automation Tools.
      Note:
      If you cannot troubleshoot with the diagnosis tool, we recommend you log in to the CVM instance via VNC and follow the instructions.

      Possible Cause

      Common login failure reasons:
      SSH key problems
      Password issues
      High bandwidth utilization
      High server load
      Improper security group rules

      Troubleshooting

      Logging in via VNC

      If you cannot log in to the Linux instance by using Orcaterm or remote login software, you can try log in with VNC for troubleshooting.
      1. Log in to the CVM console.
      2. On the Instances page, select the target instance and click Log in.
      
      
      3. In the Standard Login | Linux Instance window that pops up, select Login via VNC.
      Note:
      If you forgot the password for the instance, you can reset it in the console. For more information, see Resetting Instance Password.
      4. Enter the username and password to login.

      Login failure due to SSH issue

      Problem: During login to a Linux instance using SSH, a message appears indicating that the connection is unavailable or failed. Steps: See Unable to Use the SSH Method to Log in to a Linux Instance to perform troubleshooting.

      Login failure due to password issue

      Problem: The login attempt failed because you forgot the password, entered an incorrect password, or failed to reset your password. Solution: Reset the password for this instance in the CVM console and restart the instance. Procedure: See Resetting Instance Password for the detailed procedure.

      High bandwidth utilization

      Problem: The self-diagnosis tool shows that bandwidth utilization is too high. Procedure:
      1. Log in to the instance by using VNC login.
      2. Check the bandwidth utilization of the instance and perform troubleshooting accordingly. For details, see Login Failure Due to High Bandwidth Occupation.

      High instance load

      Problem: The self-diagnosis tool or Tencent Cloud Observability Platform shows that server CPU workload is too high, and the system is unable to perform remote connection or access is slow. Possible cause: Viruses, trojans, third-party antivirus software, application exceptions, driver exceptions, and automatic updates of software on the backend may lead to high CPU utilization, causing CVM login failures or slow access. Procedure:
      1. Log in to the instance by using VNC login.
      2. In Task manager, find the process with a high load. For more information, see Failing to log in to a Linux CVM due to high CPU and memory usage.

      Improper security group rules

      Problems: The self-diagnosis tool shows that the security group rule configuration is improper, leading to login failures. Procedure: Troubleshoot with the security group (port) verification tool.
      
      If the problem is caused by a port issue of the security group, you can use the Open all ports feature to open all ports.
      
      To define a custom rule for the security group, see Adding Security Group Rules.

      Other Solutions

      If you still cannot connect to the Linux instance, save your self-diagnosis results and submit a ticket for assistance.
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