Diagnosing CIFS Permission denied or "cifs_mount failed w/return code = -13" errors

Issue

• Attempted to mount CIFS share manually, for example:

  [root@flandre-examplebox ~]# mount -t cifs -o credentials=/etc/user-file //remilia-examplebox/  pachiouli /knowledge
  mount error(13): Permission denied
  

• Mounting using /etc/fstab with mount -a also fails:

  [root@flandre-examplebox ~]# mount -a
  mount error(13): Permission denied
  

• The following messages are present in /var/log/messages from mount attempts:

  Aug  9 22:39:39 flandre-examplebox kernel: Status code returned 0xc000006d  NT_STATUS_LOGON_FAILURE
  Aug  9 22:39:39 flandre-examplebox kernel: CIFS VFS: Send error in SessSetup = -13
  Aug  9 22:39:39 flandre-examplebox kernel: CIFS VFS: cifs_mount failed w/return code = -13
  

• The error Credential formatted incorrectly: (null) appears in verbose mount command output:

  [root@flandre-examplebox ~]# mount -vvv -t cifs -o credentials=/etc/user-file //remilia-  examplebox/pachiouli /knowledge
  ----8<---- (output trimmed)
  Credential formatted incorrectly: (null)
  mount.cifs kernel mount options: ip=123.123.123.123,unc=\\remilia-  examplebox\pachiouli,credentials=/etc/user- file,ver=1,user=USER,domain=DOMAIN,prefixpath=DOMAIN/USER,pass=********
  mount error(13): Permission denied
  Refer to the mount.cifs(8) manual page (e.g. man mount.cifs)