:What do I do if I cannot connect to a Linux instance and the "login: Module is unknown" error message appears?

Problem description

A Linux instance cannot be connected and an error message similar to the following one appears in the secure log:

login: Module is unknown.
login: PAM unable to dlopen(/lib/security/pam_limits.so): /lib/security/pam_limits.so: cannot open shared object file: No such file or directory.

Cause

For each application that has Pluggable Authentication Modules (PAM) enabled, a configuration file that is named after the application exists in the /etc/pam.d directory. For example, if the configuration file of the login command is /etc/pam.d/login, you can configure a policy in the corresponding configuration file, as described in the following table.

When you connect to the instance, some PAM-enabled applications fail to load modules. As a result, you cannot connect to the instance by using the applications. View the configurations of the /etc/pam.d/sshd file and /etc/pam.d/system-auth file. If an error occurs in the /etc/pam.d/login configuration file of the management terminal, submit a ticket to contact Alibaba Cloud technical support.

Solution

1. Connect to the Linux instance by using a management terminal. For more information, see Connect to a Linux instance by using a username and password.

2. Run the following command to view the PAM configuration file and check whether the configuration file contains the following configuration information.

   cat [$File_Name]

   Note

   [$File_Name] is the absolute path of the corresponding PAM configuration file.

   Configuration information:

3. 

4. Run the following command to check whether the pam_limits.so module file exists:

   Note

   In 64-bit Linux instances, the correct path is /lib64/security.

   ll /lib/security/pam_limits.so

5. Run the following command to change the path of the pam_limits.so module to the correct path. Then, save the path and exit.

   vi [$File_Name]

   Note

   [$File_Name] is the absolute path of the corresponding PAM configuration file.

   Modified configuration:

   session    required     /lib64/security/pam_limits.so

6. Connect to the Linux instance by using a management terminal. For more information, see Connect to a Linux instance by using a username and password.