What do I do if I fail to log on to a Linux simple application server and the

If your Linux simple application server is unreachable and the secure log contains the following error, the cause is a misconfigured Pluggable Authentication Modules (PAM) path. Specifically, pam_limits.so is referenced at the wrong location.

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.

Before you begin

Determine which PAM configuration file is affected, then decide how to proceed:

File	Controls	Action
`/etc/pam.d/sshd`	SSH logon	Fix it yourself using the steps below
`/etc/pam.d/system-auth`	System-wide authentication	Fix it yourself using the steps below
`/etc/pam.d/login`	Console (management terminal)	Submit a ticket to contact Alibaba Cloud technical support

Because SSH is blocked, you cannot log in through a normal connection. Use the rescue feature instead.

The rescue feature uses a recovery connection that allows access even when normal logon is completely blocked.

Fix the PAM configuration path

Connect to your server using the rescue feature. For details, see Connect to a Linux server by using the rescue feature.
View the PAM configuration file to confirm the incorrect path. Replace [$File_Name] with the absolute path of the configuration file — for example, /etc/pam.d/sshd:
```
cat [$File_Name]
```
Look for a line that references pam_limits.so. The configuration resembles:
Find the actual location of pam_limits.so on your system:
```
ll /lib/security/pam_limits.so
```
On 64-bit Linux instances, the correct path is /lib64/security.
Open the configuration file and update the pam_limits.so path:
```
vi [$File_Name]
```
Change the pam_limits.so line to the correct path. For 64-bit instances:
```
session    required     /lib64/security/pam_limits.so
```
Save the file and exit.
Connect to your server again to verify the fix. For details, see Connect to a Linux server.