Plesk backup finishes with warning: Unable to back up applications packages. Error: Wrong encryption key size

Symptoms

• A backup that is created via the Plesk GUI finishes with the following warning:
  

  CONFIG_TEXT: Warning: Server "example.com"
  Unable to back up applications packages. Error: Wrong encryption key size

• In the logs of the backup that is being generated, the following warning can be found:
  

  CONFIG_TEXT:  WARN [panel] Unable to back up applications packages.
   WARN [panel] Exception: Wrong encryption key size

• Errors that are similar to the following can be seen in the /var/log/sw-cp-server/sw-engine.log:

  CONFIG_TEXT: chpasswd[748392]: Failed to read entire encryption key from '/etc/psa/private/secret_key': Resource temporarily unavailable (11)
  chpasswd[748392]: Failed to initialize encryption cipher 'AES-128-CBC' with key '/etc/psa/private/secret_key'
  chpasswd[748392]: encrypt: cannot initialize encryption engine
  chpasswd[748392]: Unable to encrypt password for store in Plesk db

Cause

The /etc/psa/private/secret_key file is corrupted, due to which its size is not accurate.

Resolution

Reset the secret_key file by executing the following steps:

1. Log into your server via SSH
2. Make a backup of the corrupted file (just in case) by executing this command:

# cp /etc/psa/private/secret_key /etc/psa/private/secret_key.bak

3. Reset the/etc/psa/private/secret_key key by executing the following command:

Warning: Before the execution of this command, it is recommended to make a full backup of the Plesk database by following the information in this article.

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The output that this command will provide would be similar to the following:

ODBC error #28000: [unixODBC][ma-3.0.8]Access denied for user 'apsc'@'localhost' (using password: YES)

Executing it may result in temporary inability to run Plesk commands, due to experiencing errors that are similar to the following:

# plesk bin site --info example.com
ODBC error #28000: [unixODBC][ma-3.0.8]Access denied for user 'apsc'@'localhost'  (using password: YES)
exit status 3

4. (Optional) If you do experience the error, you can resolve it by executing the following command:

# plesk repair db