This document describes the possible causes of Linux instance login failures and troubleshooting methods, helping you detect, locate, and resolve problems.

Possible Causes

The primary causes of Linux instance login failures include:

• SSH key problems
• Password problems
• Excessive bandwidth utilization
• High server load
• Incorrect remote port configuration
• Incorrect security group rules

If you cannot check your problem by using the self-diagnose tool, we recommend that you log in to the CVM through VNC and troubleshoot step by step.

Troubleshooting

Logging in by using VNC

If you cannot use the standard method (Webshell) or remote login software to log in to a Linux instance, you can use Tencent Cloud VNC to log in and locate the problem causes.

1. Log in to the CVM console.
2. On the instance management page, select the instance to access and click Log In, as shown in the following figure:
   
3. In the "Log in to Linux Instance" window that appears, select Alternative login methods (VNC) and click Log In Now.

   During login, if you forget the password of this instance, you can reset it in the console. For more information, see Resetting the Instance Password.

4. Enter the username and password in the dialog box that appears to complete the login process.

SSH problems

Problem: during login to a Linux instance by using SSH, a message indicating that the connection is unavailable or failed appears.
Steps: see Unable to Log In to a Linux Instance by Using SSH for troubleshooting.

Password problems

Problem: unable to log in because you forget the password, enter it incorrectly, or fail to reset it.
Solution: reset the password of this instance in the Tencent Cloud console, and restart the instance.
Steps: for information on how to reset the password of an instance, see Resetting the Instance Password.

Excessive bandwidth utilization

Problem: the self-diagnosis tool shows that bandwidth utilization is too high.
Steps:

1. Log in to the instance by using VNC.
2. Check the bandwidth utilization of the instance and troubleshoot accordingly. For details, see Unable to Log In Due to High Bandwidth Utilization.

High server load

Problem: Cloud Monitor shows that load of the server CPU is high, and the system cannot be accessed remotely or access is slow.
Possible Causes: viruses, trojans, third-party anti-virus software, application exceptions, driver exceptions, and software backend automatic updates may lead to high CPU usage, causing CVM login failures or slow access.
Steps:

1. Log in to the instance by using VNC.
2. In "Task manager", find the process with a high load. For details, see Unable to Log In Due to High CPU and Memory Usage.

Incorrect remote port configuration

Problem: the remote port is inaccessible, the remote access port is not the default port or has been modified, or port 22 is not open.
Diagnosis: check whether the public IP address of the instance can be pinged through. Run the telnet command to check whether the port is open.
Steps: see Unable to Log In Remotely Due To Port Issues.

Incorrect security group rules

Problem: unable to log in due to incorrect security group rules.
Steps: troubleshoot by using the port verification tool for security groups.

If the problem is caused by the incorrect security group port configuration, you can use Open All Tools to open all ports.

If you need to define a custom rule for the security group, see Adding Rules to Security Groups for information on how to reconfigure security group rules.

Other Solutions

If you still cannot log in to the Linux instance after trying the preceding troubleshooting methods, save your self-diagnosis results and submit a ticket.