HOST: Kubuntu 16.04.3 LTS

LOCALHOST: Kubuntu 17.10

I'm not able anymore to mount a cifs share on a terminal:

mount -t cifs -o user=USER,domain=DOMAIN //HOST/share /mnt/tmp
Password for USER@//HOST/share:  *************
mount error(5): Input/output error
Refer to the mount.cifs(8) manual page (e.g. man mount.cifs)

In syslog I found the error messages when attempting:

Status code returned 0xc000005e STATUS_NO_LOGON_SERVERS
CIFS VFS: Send error in SessSetup = -5
CIFS VFS: cifs_mount failed w/return code = -5

I'm sure this is a working share with sufficient permissions for that user. I can start dolphin and open smb://HOST/share without any problems!

My system is in an Active Directory environment (realm, sssd) and I also tried to mount using a kerberos ticket but faild:

mount -t cifs -o user=USER,domain=DOMAIN,cruid=USER,sec=krb5 //HOST/Share /mnt/tmp
mount error(2): No such file or directory
Refer to the mount.cifs(8) manual page (e.g. man mount.cifs)

In syslog I found this error messages when attempting:

CIFS VFS: Send error in SessSetup = -2
CIFS VFS: cifs_mount failed w/return code = -2

SSO via kerberos is working! Using smb://HOST/share on dolphin I can open the share without a password.

Also I can login to the share using

smbclient -U USER //HOST/share

and I can list files there using 'ls'.

I found someone in with the same error in the internet but he could solve it by uninstalling winbind. Unfortunately I have no winbind installed on both machines and so this is not a fix for me. Someone else needed to add the workgroup name, which is not working for me too. Also I found to use a different smb version for mounting. Unfortunately it always fails with "cifs_mount faild w/return code = -5" (vers=1.0, vers=2.0, vers=2.1, vers=3.0, vers=3.1.1).

I could reproduce this error between two clients with both LTS or latest release 16.04<->16.04 and 17.10<->17.10.

Interesting: mounting is working if I mount a Windows share and not a linux samba share!

What is the reason for cifs_mount error -5?


  • Did you try mount.cifs //HOST/share /mnt/tmp -o user=USER,domain=DOMAIN? (just to make a variation on the same theme) Nov 24, 2017 at 12:51
  • yes I tried appending the options and still faild with that error.
    – Alexander
    Nov 24, 2017 at 14:30

2 Answers 2


I recommend you use fstab for mounting.

Try to check the logs to troubleshoot the causes of your problem, try this command to display the list of files which could display the mount logs:

grep -e mount -e ext4 -lR /var/log 2> /dev/null

For me, the mount logs were in /var/log/syslog it may be different for you.

Now you need two terminal tabs open, enter the command on one tab: sudo tail -f /var/log/syslog

And on the second tab, try to mount the system with the following command:

mount -t cifs -o user=USER,domain=DOMAIN,cruid=USER,sec=krb5 //HOST/Share /mnt/tmp

If you go back to your first tab you should be able to see some log errors. For me the errors were(for you it may be different):

   kernel: No dialect specified on mount. Default has changed to a more secure dialect, SMB2.1 or later (e.g. SMB3), from CIFS (SMB1). To use the less secure SMB1 dialect to access old servers which do not support SMB3 (or SMB2.1) specify vers=1.0 on mount.
   kernel: CIFS VFS: protocol revalidation - security settings mismatch
   kernel: CIFS VFS: session ffff90a6a2959000 has no tcon available for a dfs referral request
   kernel: CIFS VFS: cifs_mount failed w/return code = -5

Depending on your error logs, you may be able to get away with adding vers=1.0 to your mount command and this could work but it is the less secure version of smb. Otherwise, you could workout what the solution is based on the error you get.

What you could also try is configure the Samba server inside /etc/samba/smb.conf similar to this (it works for me):

   comment = Username's developer directory
   read only = no
   locking = no
   path = /var/www/username
   guest ok = no
   writeable = yes

Then on the client, add the following line to /etc/fstab

//server/username /mountpoint cifs vers=1.0,username=username,iocharset=utf8,uid=your_profile_uid_on_the_server 0 0

Use sudo mount /mountpint See how this goes, hopefully this information will be useful to you.


I'd like to answer my own question (SOLVED):

I put my clients into AD by realm, using SSSD and no winbind. SSSD does not support NTLM authentication that's why user/password authentication is not working on linux samba shares but on windows shares. With samba 4.8 winbind is required and so I use SSSD + winbind in combination. Now user/password authentication on samba shares is working!

You need to join clients to AD with

realm join --user=$USER --user-principal=host/$(hostname -s)@DOMAIN --automatic-id-mapping=no --client-software=sssd --membership-software=samba --computer-name=$(hostname -s) --os-name="$(grep NAME /etc/os-release | head -1 | sed 's/NAME="\(.*\)"/\1/g')" --os-version=$(grep VERSION_ID /etc/os-release | sed 's/VERSION_ID="\(.*\)"/\1/g') DOMAIN

your smb.conf needs the [global] options for winbind to use sss as backend

   idmap config DOMAIN : backend        = sss
   idmap config DOMAIN : range          = <min>-<max>

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