Unable to connect to Plesk via SFTP: Authentication failed: Failed to connect to system bus: Permission denied

Symptoms

• Unable to connect to Plesk server via SFTP with the error (e.g. from FileZilla):

  Error: Authentication failed.
  Error: Critical error: Could not connect to server

• The following error is observed in /var/log/secure:

  proftpd: pam_env(proftpd:setcred): Unable to open
  config file: /etc/security/pam_env.conf: Permission denied
  proftpd: pam_systemd(proftpd:session): Failed to connect to system bus: Permission denied
  proftpd: pam_unix(proftpd:session): session closed for user user
  Received unexpected end-of-file from SFTP server

• The system user of the subscription is used to log in over SFTP

Cause

Access to the server over SSH is set to Forbidden in Domains > example.com > Web Hosting Access.

Resolution

1. Log into Plesk
2. Navigate to Plesk> Domains > example.com > Web Hosting Access
3. Make sure that the field Access to the server over SSH is set to any available shell (but not to Forbidden).
   For example, /bin/sh: