Comment 22 for bug 1729337

I've done further tests, and found that with kernels 3.13.0-128, 3.13.0-133, 3.13.0-134 and 3.13.0-135, mounting cifs folder using vers=3.0 (with no security mode manually set, ie: no option sec=ntlmsspi used) sometimes work and sometimes it doesn't, unfortunately I can't figure out what is causing this; if anyone has any ideas please let me know.

It's so weird that sometimes after a fresh boot, I can see that the mount points from the fstab aren't mounted so if I do either sudo mount -a or sudo mount -o remount -a it sometimes crashes and sometimes it works and successfully mount the folders, see below example:

# Fresh boot
$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 14.04.5 LTS
Release: 14.04
Codename: trusty

# In this example I'm using 3.13.0-128, but same behaviour with newer kernels
$ uname -a
Linux ruby2-staging03 3.13.0-128-generic #177-Ubuntu SMP Tue Aug 8 11:40:23 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux

$ ll /mnt/apps
total 8
drwxr-xr-x 2 root root 4096 Nov 19 2015 ./
drwxr-xr-x 9 root root 4096 Aug 10 17:54 ../

$ sudo mount -a
- OR -
$ sudo mount -o remount -a
mount error(22): Invalid argument
Refer to the mount.cifs(8) manual page (e.g. man mount.cifs)
mount error(22): Invalid argument
Refer to the mount.cifs(8) manual page (e.g. man mount.cifs)
mount error(22): Invalid argument
Refer to the mount.cifs(8) manual page (e.g. man mount.cifs)
mount error(22): Invalid argument
Refer to the mount.cifs(8) manual page (e.g. man mount.cifs)
mount error(22): Invalid argument
Refer to the mount.cifs(8) manual page (e.g. man mount.cifs)
mount error(22): Invalid argument
Refer to the mount.cifs(8) manual page (e.g. man mount.cifs)

# try again, could fail every time but sometimes it does succeeds and mount the files:
$ sudo mount -a
- OR -
$ sudo mount -o remount -a

$ ll /mnt/apps
total 25
drwxrwx--- 2 root root 4096 Aug 21 14:38 ./
drwxr-xr-x 9 root root 4096 Aug 10 17:54 ../
-rw-rw---- 1 root root 0 Aug 10 21:04 test
drwxrwx--- 2 root root 0 Oct 21 2015 tmp/

# Relevant entry from /etc/fstab:
//some_server/Applications /mnt/apps cifs vers=3.0,iocharset=utf8,noperm,rw,uid=root,file_mode=0660,dir_mode=0770,credentials=/credentials 0 0

Cheers
FedeX