I'm trying to set up Single Sign On (SSO) with Kerberos and LDAP but I have an issue with NFSv4 with Kerberos for authentication and encryption (krb5p) service.

My environment:

  • 1 server (named server) with LDAP and Kerberos (IP:
  • 1 server (named host2) with services such as SSH and NFSv4 (IP:
  • 1 client (named host1) (IP:

The three machines are running Ubuntu 18.04.

My /etc/hosts is the same on the three machines see below.

SSO is well working with SSH service with GSSAPI, I have the good Kerberos ticket on my client. Now I'm trying to set up NFSv4 service. First I configured the shared files (nfs-kernel-server and nfs-common)

When I'm logging with LDAP user on the client machine (with sssd) and mount the shared directory everything seems ok.

sudo mount -vvv -t nfs4 -o proto=tcp,port=2049,sec=krb5p host2.stagenfs.fr:/ /mnt

Note that I had to add right to LDAP user in /etc/sudoers in order to mount NFS directory with LDAP user account:


<LDAP user> ALL=(ALL:ALL) NOPASSWD: /bin/mount,/bin/umount,/sbin/mount.nfs,/sbin/mount.nfs4

But Kerberos gives me a ticket which belongs to root (with 600 permissions). So I'm unable to go into /mnt directory when I'm log in with the LDAP client account. So I found that only root user can access to /mnt. On client (mount point directory) and server, NFS shared directories have 777 permissions.

The LDAP user ticket is in the directory specified in sssd.conf file but the ticket for NFS service is in the /tmp/ directory.

I tried a chown <LDAP user>:<LDAP user group> /tmp/krb5ccmachine_STAGENFS and then my LDAP user was able to access /mnt

I think that may come from the idmapd service but don't understand how to set up /etc/idmapd.conf to get things ok. I tried some configuration I found on the web but none worked.

Here my conf files:

/etc/hosts (same on all machines)   localhost

# The following lines are desirable for IPv6 capable hosts
::1     ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters     server.stagenfs.fr      server     stagenfs.fr     host1.stagenfs.fr       host1   host2.stagenfs.fr       host2

/etc/nsswitch.conf (same on all machines)

# /etc/nsswitch.conf
# Example configuration of GNU Name Service Switch functionality.
# If you have the `glibc-doc-reference' and `info' packages installed, try:
# `info libc "Name Service Switch"' for information about this file.

passwd:         compat systemd sss
group:          compat systemd sss
shadow:         compat sss
gshadow:        files

hosts:          files mdns4_minimal [NOTFOUND=return] dns myhostname
networks:       files

protocols:      db files
services:       db files sss
ethers:         db files
rpc:            db files

netgroup:       nis sss
sudoers:        files sss

/etc/idmapd.conf (same on client and NFS server)


Verbosity = 5
Pipefs-Directory = /run/rpc_pipefs
# set your own domain here, if it differs from FQDN minus hostname
Domain = stagenfs.fr
Local-Realms = STAGENFS.FR


Nobody-User = nobody
Nobody-Group = nogroup

#Method = nsswitch
Method = static
GSS-Methods = static
#Method = umich_ldap,nsswitch
#GSS-Methods = umich_ldap
#Method = sss

#nfs/host1.stagenfs.fr@STAGENFS.FR = alice
#nfs/host1@STAGENFS.FR = alice
#nfs/host2@STAGENFS.FR = alice
alice@STAGENFS.FR = alice


#LDAP_server = server.stagenfs.fr
#LDAP_base = ou=tl
#LDAP_use_ssl = true
#LDAP_ca_cert = /etc/ssl/certs/cacert.pem
#NFSV4_person_objectclass = posixaccount
#NFSV4_name_attr = uid

/etc/default/nfs-common (client machine)


# Do you want to start the gssd daemon? It is required for Kerberos mounts.


/etc/default/nfs-kernel-server (NFS server machine)

# Number of servers to start up

# Runtime priority of server (see nice(1))


# Do you want to start the svcgssd daemon? It is only required for Kerberos
# exports. Valid alternatives are "yes" and "no"; the default is "no".

# Options for rpc.svcgssd.

/etc/sssd/sssd.conf (same on client and NFS server)

debug_level = 0xFFF0
config_file_version = 2
services = nss,pam
domains = STAGENFS.FR

debug_level = 0xFFF0
filter_users = root
filter_groups = root

debug_level = 10
offline_credentials_expiration = 1

debug_level = 0xFFF0
ldap_schema = rfc2307
ldap_search_base = ou=tl

id_provider = ldap
auth_provider = krb5
chpass_provider = krb5
access_provider = ldap

ldap_sasl_mech = GSSAPI
ldap_krb5_keytab = /etc/krb5.keytab

ldap_access_order = filter
ldap_access_filter = &(objectClass=posixAccount) (uidNumber=*)

ldap_uri = ldaps://server.stagenfs.fr
ldap_referrals = False
ldap_id_use_start_tls = False
cache_credentials = False
account_cache_expiration = 1
enumerate = True
ldap_default_bind_dn = cn=proxyuser,ou=private,ou=tl
ldap_default_authtok_type = password
ldap_default_authtok = ProxyUser123#
ldap_tls_cacert = /etc/ssl/certs/cacert.pem

krb5_realm = STAGENFS.FR
krb5_canonicalize = False
krb5_server = server.stagenfs.fr
krb5_kpasswd = server.stagenfs.fr
krb5_ccachedir = /home/tl/%u

/var/log/syslog (with minimal configuration) (on NFS server)

Aug  2 10:05:57 host2 rpc.idmapd[470]: nfsdcb: authbuf=gss/krb5p authtype=user
Aug  2 10:05:57 host2 rpc.idmapd[470]: nfs4_uid_to_name: calling nsswitch->uid_to_name
Aug  2 10:05:57 host2 rpc.idmapd[470]: nfs4_uid_to_name: nsswitch->uid_to_name returned 0
Aug  2 10:05:57 host2 rpc.idmapd[470]: nfs4_uid_to_name: final return value is 0
Aug  2 10:05:57 host2 rpc.idmapd[470]: Server : (user) id "0" -> name "root@stagenfs.fr"
Aug  2 10:05:57 host2 rpc.idmapd[470]: nfsdcb: authbuf=gss/krb5p authtype=group
Aug  2 10:05:57 host2 rpc.idmapd[470]: nfs4_gid_to_name: calling nsswitch->gid_to_name
Aug  2 10:05:57 host2 rpc.idmapd[470]: nfs4_gid_to_name: nsswitch->gid_to_name returned 0
Aug  2 10:05:57 host2 rpc.idmapd[470]: nfs4_gid_to_name: final return value is 0
Aug  2 10:05:57 host2 rpc.idmapd[470]: Server : (group) id "0" -> name "root@stagenfs.fr"

output of commands lines on the client (host1) Alice is a LDAP user authentified with Kerberos.

alice@host1:~$ sudo mount -vvv -t nfs4 -o proto=tcp,port=2049,sec=krb5p host2:/users /mnt
mount.nfs4: timeout set for Thu Aug  2 10:07:58 2018
mount.nfs4: trying text-based options 'proto=tcp,port=2049,sec=krb5p,vers=4.2,addr=,clientaddr='

alice@host1:~$ ldapwhoami 
SASL/GSSAPI authentication started
SASL username: alice@STAGENFS.FR
SASL data security layer installed.

alice@host1:~$ klist 
Ticket cache: FILE:/home/tl/alice/krb5_25002
Default principal: alice@STAGENFS.FR

Valid starting       Expires              Service principal
02/08/2018 10:57:40  02/08/2018 20:57:40  krbtgt/STAGENFS.FR@STAGENFS.FR
    renew until 03/08/2018 10:57:40
02/08/2018 10:57:56  02/08/2018 20:57:40  ldap/server.stagenfs.fr@STAGENFS.FR
    renew until 03/08/2018 10:57:40

alice@host1:~$ klist -c /tmp/krb5ccmachine_STAGENFS.FR 
klist: Credentials cache permissions incorrect (filename: /tmp/krb5ccmachine_STAGENFS.FR)

root@host1:~# klist -c /tmp/krb5ccmachine_STAGENFS.FR 
Ticket cache: FILE:/tmp/krb5ccmachine_STAGENFS.FR
Default principal: host/host1.stagenfs.fr@STAGENFS.FR

Valid starting       Expires              Service principal
02/08/2018 10:01:07  02/08/2018 20:01:07  krbtgt/STAGENFS.FR@STAGENFS.FR
    renew until 03/08/2018 10:01:07
02/08/2018 10:01:07  02/08/2018 20:01:07  nfs/host2.stagenfs.fr@STAGENFS.FR
    renew until 03/08/2018 10:01:07

root@host1:~# klist -k /etc/krb5.keytab 
Keytab name: FILE:/etc/krb5.keytab
KVNO Principal
---- --------------------------------------------------------------------------
   2 ldap/server.stagenfs.fr@STAGENFS.FR
   2 ldap/server.stagenfs.fr@STAGENFS.FR
   2 host/server.stagenfs.fr@STAGENFS.FR
   2 host/server.stagenfs.fr@STAGENFS.FR
   2 host/host1.stagenfs.fr@STAGENFS.FR
   2 host/host1.stagenfs.fr@STAGENFS.FR
   2 host/host2.stagenfs.fr@STAGENFS.FR
   2 host/host2.stagenfs.fr@STAGENFS.FR
   2 nfs/host2.stagenfs.fr@STAGENFS.FR
   2 nfs/host2.stagenfs.fr@STAGENFS.FR

As you can see, I tried several methods for idmapd.conf but I didn't manage to get this working. I found some website such as this one link but it didn't help. I think I'm missing something in idmapd configuration or maybe somewhere else. If you have any idea or questions, don't hesitate.

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