Setting up Samba as a Domain Member

Introduction

In the context of Samba, you usually only hear about servers (AD DCs, NT4 PDCs, file servers, etc.). You usually do not hear much about a Samba workstation as a Domain Member, similar to hosts running a version of Windows e. g. Windows 10 Pro or some other workstation edition. What if you want to join a Linux workstation to the domain, to authenticate user logins against your Domain Controller(s)?

Generally speaking, a Samba server is just a Samba workstation that provides file shares or print services. This is how we will structure our documentation here - being a Domain Member is the prerequisite for configuring a Samba file and/or print server.

See the server information used in documentation page for paths used, hostnames, etc.

Installation

You have the following options to install Samba:

• Build Samba yourself

• Install distribution specific packages

• Install SerNet Samba+/Enterprise packages

Preparing the host for the domain join

AD DNS zone resolution

Many things in an Active Directory, such as Kerberos, rely on DNS. Therefore it is required that the host is able to resolve AD DNS zones. If you have multiple DCs acting as a DNS server, it's recommended to setup multiple nameserver entries for fail over reasons.

On Linux and Unixes, you usually configure DNS settings in /etc/resolv.conf:

nameserver 10.99.0.1
nameserver 10.99.0.2
search samdom.example.com

Some tools, such as NetworkManager, may overwrite manual changes in that file. Please consult your distributions documentation for configuring name resolution.

To verify a correct name resolution, try resolving the hostname of one of your Domain Controllers:

# host -t A DC1.samdom.example.com
DC1.samdom.example.com has address 10.99.0.1

NTP

In an Active Directory, accurate time synchronization is necessary for Kerberos, to prevent replay attacks and for resolving directory replication conflicts. For those reasons, if the time differs to your AD, your host won't be able to access AD servers and any shares it provides won't be accessible by others.See Time syncronisation for further information and configuration examples.

Local hostname resolution

During the Domain join, Samba tries to register/update the hosts name and IP in your AD DNS. This requires that "net" can resolve both, either via DNS or /etc/hosts. To verify, run

# getent hosts M1
10.99.0.5      M1.samdom.example.com    M1

The commands output must show the correct LAN interface IP (not 127.*.*.*!) and the hostname including the AD DNS zone. Additional alias names are optional. If you get a different output, fix it in your DNS or by adding/changing the /etc/hosts entry:

10.99.0.5      M1.samdom.example.com    M1

Setup a Domain Member smb.conf file

Before joining a domain, it's necessary to create Sambas configuration file "smb.conf". The following command shows, where the file is located in your installation:

# smbd  -b | grep CONFIGFILE
  CONFIGFILE: /usr/local/samba/etc/smb.conf

In the following you see an smb.conf example sufficient to join a domain, if you add an "idmap config" part, fitting to your environment:

[global]

       netbios name = M1
       security = ADS
       workgroup = SAMDOM
       realm = SAMDOM.EXAMPLE.COM

       log file = /var/log/samba/%m.log
       log level = 1

       dedicated keytab file = /etc/krb5.keytab
       kerberos method = secrets and keytab
       winbind refresh tickets = yes

       winbind trusted domains only = no
       winbind use default domain = yes
       winbind enum users  = yes
       winbind enum groups = yes
 
       # idmap config used for your domain.
       # Click on the following links for more information
       # on the available winbind idmap backends, 
       # Choose the one that fits your requirements
       # then add the corresponding configuration. 
       
       # Just adding the following three lines is not enough!!
       #  - idmap config ad
       #  - idmap config rid
       #  - idmap config autorid

See the manpage of "smb.conf" for detailed information about the parameters and options used.

The domain join

A note on provisioning: A Domain Member must not be provisioned via "samba-tool"! This process isn't implemented yet.

The following command will join the host to the domain and automatically register/update its DNS record:

# net ads join -U administrator
Enter administrator's password: Passw0rd
Using short domain name -- SAMDOM
Joined 'M1' to dns domain 'samdom.example.com'

If you encounter any error message(s), see Troubleshooting error messages during Domain Member join.

libnss_winbind

Domain users and groups are made available to your local system through libnss_winbind. The smb.conf configuration was already done in a previous step. Next is to tell your system to retrieve that information from winbindd by adding "winbind" to the following two lines of your /etc/nsswitch.conf:

passwd: files winbind
group:  files winbind

Keep the existing database "files" (sometimes you may find "compat" instead of "files"). It defines that accounts and groups are first looked up in local files (/etc/passwd and /etc/group), then via Winbindd.

Note: you cannot have users & groups with the same name in the local files and the domain i.e. a user 'foo' that appears in /etc/passwd would be the same user as 'DOMAIN\foo', in this instance you would need to remove or rename one of the users.

Important: If you have compiled Samba, you may need to add two symbolic links. See libnss_winbind links for OS specific information on where to place them. Samba package installations usually place the file directly in the OS library path or have the links included.

Start daemons

Depending on how you use your Domain Member, you have to start different daemons:

For a pure Domain Member (domain logons only):

# winbindd

For Domain Members sharing directories (file server) and/or printers (print server):

# smbd
# nmbd
# winbindd

If you installed Samba via packages, you usually have init scripts or systemd/upstart support included. If you have compiled Samba, you need to do write your own scripts. See the init script page for examples. For automatic startup of the service(s) at boot time, please consult you distributions documentation.

Testing Winbindd user/group retrieval

wbinfo

You first need to check that Winbindd is able to retrieve domain users and groups. On a successful setup, the following commands will print all users/groups in your domain:

# wbinfo -u
administrator
krbtgt
guest
...

# wbinfo -g
enterprise admins
domain computers
domain admins
...

Using domain accounts/groups in OS commands

If you have correctly included libnss_winbind in your system, the following commands should print all local system users/groups, followed by any local Unix users/groups and then the ones from the domain (see /etc/nsswitch.conf order):

# getent passwd
root:x:0:0:root:/root:/bin/bash
bin:x:1:1:bin:/bin:/sbin/nologin
daemon:x:2:2:daemon:/sbin:/sbin/nologin
...
demo01:*:10000:10000:demo01:/home/demo01:/bin/bash
...

# getent group
root:x:0:
bin:x:1:
daemon:x:2:
...
domain admins:x:10001:
domain users:x:10000:
...

Note: If you're not getting domain accounts/groups in that output, verify that

• libnss_winbind configuration is correct - expecially if "ldconfig" is able to find "libnss_winbind.so.2" and "libnss_winbind.so"
• if using idmap config ad, accounts/groups have RFC2307 attributes set
• "winbind enum users" and "winbind enum groups" are set to "yes" in your smb.conf

Any domain accounts/groups shown by getent or id can be used in the OS, i.e.

# id demo01
uid=10000(demo01) gid=10000(domain users) groups=10000(domain users),2001(BUILTIN\users)

# chown demo01:"domain users" file.txt
# ls -s file.txt
-rw-------. 1 demo01 domain users 992  18. Oct 2015  file.txt

Authenticating Domain users via PAM

If you have setup this Domain Member as a server providing file shares or print services, you may want to skip this part, By following this part, you will allow domain users to logon locally to the hosts console.

General information

Important note: Before you start changing your PAM configuration:

• make sure you know what you're doing!
• before you start, login within a second terminal and keep it open until everything works as expected. Otherwise, you may lockout yourself and won't be able to login again!

If you have compiled Samba, you need to add a symbolic links. See pam_winbind link for OS specific information, where to place it. Samba package installations usually place the file directly in the right folder or have a link included.

Configure PAM

Note: Whenever your distribution ship tools to configure PAM, it's recommended to use them, instead of manually editing the configuration files!

• Red Hat based OS: authconfig/authconfig-tui
• Debian based OS: pam-auth-update
• SUSE based OS: yast

For manual changes: Typically the PAM configuration files are located in /etc/pam.d/ Depending on your distribution, the filename(s) may differ. E. g. on RHEL, you configure system login authentication in /etc/pam.d/password-auth-ac:

#%PAM-1.0
auth        required      pam_env.so
auth        sufficient    pam_unix.so nullok try_first_pass
auth        requisite     pam_succeed_if.so uid >= 1000 quiet_success
auth        sufficient    pam_winbind.so use_first_pass                    # <-- add this line
auth        required      pam_deny.so

account     required      pam_unix.so broken_shadow
account     sufficient    pam_localuser.so
account     sufficient    pam_succeed_if.so uid < 1000 quiet
account     [default=bad success=ok user_unknown=ignore] pam_winbind.so    # <-- add this line
account     required      pam_permit.so

password    requisite     pam_cracklib.so try_first_pass retry=3 type=
password    sufficient    pam_unix.so sha512 shadow nullok try_first_pass use_authtok
password    sufficient    pam_winbind.so use_authtok                       # <-- add this line
password    required      pam_deny.so

session     optional      pam_keyinit.so revoke
session     required      pam_limits.so
session     [success=1 default=ignore] pam_succeed_if.so service in crond quiet use_uid
session     required      pam_unix.so

For additional information about PAM configuration and settings used in the example above, please consult the PAM documentation and the manpages of pam.conf and pam_winbind.

Verify domain user login

Try to login on the local console with a domain user account:

CentOS Linux 7 (Core)
Kernel 3.10.0-229.11.1.el.7.x86_64 on an x86_64

M1 login: demo01
Password: Passw0rd

[demo01@M1 ~]$ _

Setting up additional services

Now you have successfully made your host be a Domain Member, you can, as on a Windows OS, additionally share directories (file server) or act as an print server.