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# Active Directory integration (Magyar)

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From Wikipedia:

  Active Directory (AD) is a directory service that Microsoft developed for Windows domain networks.

This article describes how to integrate an Arch Linux system with an existing Windows domain network using Samba.

Before continuing, you must have an existing Active Directory domain, and have a user with the appropriate rights within the domain to: query users and add computer accounts (Domain Join).

This document is not an intended as a complete guide to Active Directory nor Samba. Refer to the resources section for additional information.

## Bevezetés

This article explains how to configure an Arch Linux system to participate in an Active Directory domain. This article was written and tested on a fresh installation, and it is assumed that all configuration files are in their unmodified, post-installation state. For the duration of the article, the example Active Directory domain will use the following configuration:

- NetBIOS domain name: INTERNAL
- DNS domain name: internal.domain.tld
- Kerberos realm: INTERNAL.DOMAIN.TLD
- First DC: server1.internal.domain.tld with IP address 192.168.1.1
- Second DC: server2.internal.domain.tld with IP address 192.168.1.2

In most small networks, the DCs (domain controllers) also hold the DNS server role. This may not be true in larger networks. Generally, DCs also hold the NTP role, but not always. Consult your network administrator to verify correct values for DNS and NTP servers.

## Needed software

In order to use samba effectively, you will need to install the following packages: samba, smbclient, and ntp. (timedatectl can be used as an alternative to ntp.)

Additionally, while not required, the following packages will be useful for testing and troubleshooting: bind, krb5, and if a printing is desired (whether you want to share printers, or use printers on another Samba/Windows host), cups.

## Szolgáltatások kezdeti beállítása

### DNS configuration

Active Directory depends entirely on DNS for name resolution. It is imperative that the `/etc/resolv.conf` file is configured with both the correct DNS servers and a domain search suffix. Whether configured via DHCP or static configuration, ensure that these values are correct for your domain. For the example domain configuration, the following contents are appropriate (be sure to replace 192.168.1.1, 192.168.1.2, and internal.domain.tld with appropriate values for your network):

    /etc/resolv.conf

    nameserver 192.168.1.1
    nameserver 192.168.1.2
    search internal.domain.tld

If you elected to install the bind package, you can test DNS configuration with the following commands (be sure to replace server1 and internal.domain.tld with appropriate values for your network):

    $ nslookup -type=SRV _kerberos._tcp.internal.domain.tld.
    $ nslookup -type=SRV _ldap._tcp.internal.domain.tld.
    $ nslookup server1.internal.domain.tld.

You should get output similar to the following (adjust appropriately for only one DC, or more than two):

    Server:        192.168.1.1
    Address:       192.168.1.1#53

    _kerberos._tcp.internal.domain.tld service = 0 100 88 server1.internal.domain.tld.
    _kerberos._tcp.internal.domain.tld service = 0 100 88 server2.internal.domain.tld.
    ...
    _ldap._tcp.internal.domain.tld     service = 0 100 389 server1.internal.domain.tld.
    _ldap._tcp.internal.domain.tld     service = 0 100 389 server2.internal.domain.tld.
    ...
    Name:   server1.internal.domain.tld
    Address: 192.168.1.1

### NTP configuration

In an Active Directory domain, more specifically for Kerberos ticketing, it is imperative that time is synchronized with all other hosts on the network. A margin of error no more than five minutes is required. For the example domain configuration, an appropriate `/etc/ntp.conf` file should have the following contents (be sure to replace server1, server2, and internal.domain.tld with appropriate values for your network):

    /etc/ntp.conf

    # Use your domain's NTP servers
    server server1.internal.domain.tld
    server server2.internal.domain.tld

    # Restrictions
    restrict default kod limited nomodify nopeer noquery notrap
    restrict 127.0.0.1
    restrict ::1

    # Location of drift file
    driftfile /var/lib/ntp/ntpd.drift

Enable and start the `ntpd.service` unit.

### Kerberos configuration

The Samba documentation recommends a minimal Kerberos configuration, with just enough information in the [libdefaults] section to hand off the work of discovering domain details to DNS. Unfortunately, this does not work well in practice. Continuing with the example domain configuration, modify the `/etc/krb5.conf` file with the following contents (be sure to replace instances of INTERNAL, internal.domain.tld, SERVER1, and INTERNAL.DOMAIN.TLD with appropriate values for your network):

    /etc/krb5.conf

    [libdefaults]
       default_realm = INTERNAL.DOMAIN.TLD
       dns_lookup_realm = false
       dns_lookup_kdc = true

    [realms]
       INTERNAL.DOMAIN.TLD = {
          kdc = SERVER1.INTERNAL.DOMAIN.TLD
          default_domain = INTERNAL.DOMAIN.TLD
          admin_server = SERVER1.INTERNAL.DOMAIN.TLD
       }
       INTERNAL = {
          kdc = SERVER1.INTERNAL.DOMAIN.TLD
          default_domain = INTERNAL.DOMAIN.TLD
          admin_server = SERVER1.INTERNAL.DOMAIN.TLD
       }

    [domain_realm]
        .internal.domain.tld = INTERNAL.DOMAIN.TLD

    [appdefaults]
        pam = {
            ticket_lifetime = 1d
            renew_lifetime = 1d
            forwardable = true
            proxiable = false
            minimum_uid = 1
        }

### Samba configuration

#### Base Samba configuration file

A default installation of samba does not ship with an example `/etc/samba/smb.conf` file. For our example domain configuration, use the following base settings (replace instances of INTERNAL and INTERNAL.DOMAIN.TLD with appropriate values for your network):

    /etc/samba/smb.conf

    [global]
       workgroup = INTERNAL
       security = ADS
       realm = INTERNAL.DOMAIN.TLD

       winbind refresh tickets = Yes
       vfs objects = acl_xattr
       map acl inherit = Yes
       store dos attributes = Yes

       # Allow a single, unified keytab to store obtained Kerberos tickets
       dedicated keytab file = /etc/krb5.keytab
       kerberos method = secrets and keytab

       # Do not require that login usernames include the default domain
       winbind use default domain = yes

If you do not wish to share local printers configured in cups, then add the following to the [Global] section of the `/etc/samba/smb.conf` file:

    /etc/samba/smb.conf

    [Global]
    ...
       load printers = no
       printing = bsd
       printcap name = /dev/null
       disable spoolss = yes
    ...

The remainder of the configuration depends on whether your domain supports RFC2307 Unix/NFS Attributes. Consult with your domain administrator if unsure.

##### Adding the idmap configuration for domains with RFC2307 extensions

Be certain that the values below do not overlap with system values, and that all users have at least the uidNubmer attribute, and that those users' PrimaryGroup has a gid attribute. Append to the following to the [Global] section of the `/etc/samba/smb.conf` file (replace INTERNAL with the NetBIOS domain name):

    /etc/samba/smb.conf

    [Global]
    ...

       # UID/GID mapping for local users
       idmap config * : backend = tdb
       idmap config * : range = 3000-7999

       # UID/GID mapping for domain users
       idmap config INTERNAL : backend = ad
       idmap config INTERNAL : schema_mode = rfc2307
       idmap config INTERNAL : range = 10000-999999
       idmap config INTERNAL : unix_nss_info = yes

       # Template settings for users without ''unixHomeDir'' and ''loginShell'' attributes
       template shell = /bin/bash
       template homedir = /home/%U

       # Allow offline/cached credentials and ticket refresh
       winbind offline logon = yes
       winbind refresh tickets = yes
    ...

Additionally, if user accounts in AD have a gidNumber attribute, you can use it instead of the RID for the user's Primary Group by appending the following setting (again in the [Global] section):

    /etc/samba/smb.conf

    [Global]
    ...
       idmap config INTERNAL:unix_primary_group = yes
    ...

##### Adding the idmap configuration for domains without RFC2307 extensions

If your administrator has not extended the AD schema to include the RFC2307 attributes, use the following idmap configuration in the [Global] section of the `/etc/samba/smb.conf` file (replace INTERNAL with the NetBIOS domain name):

    /etc/samba/smb.conf

    [Global]
    ...
       # UID/GID mapping for local users
       idmap config * : backend = tdb
       idmap config * : range = 3000-7999

       # UID/GID mapping for domain users
       idmap config INTERNAL : backend = rid
       idmap config INTERNAL : range = 10000-999999

       # Template settings for users
       template shell = /bin/bash
       template homedir = /home/%U

       # Allow offline/cached credentials and ticket refresh
       winbind offline logon = yes
       winbind refresh tickets = yes
    ...

## Joining the domain

To join the AD domain, simply issue the following command (be sure to replace Administrator with a user that has privileges to join the AD domain).

    # net ads join -U Administrator

## Start the individual Samba services

Enable and start the `smb.service`, `nmb.service`, and `winbind.service` services.

## Configure NSS

Modify the `/etc/nsswitch.conf` file to allow Samba to map names to uid and gid:

    /etc/nsswitch.conf

    ...
    passwd: files winbind mymachines systemd
    group: files winbind mymachines systemd
    ...

### Testing NSS

Verify connectivity by listing the AD domain users and groups that system is aware of:

    # wbinfo -u
    # wbinfo -g

You should get a list of AD users followed by AD groups.

## Configuring PAM authentication

Rather than configuring options directly in the Linux-PAM configuration files, set defaults for the pam_winbind module in `/etc/security/pam_winbind.conf`:

    /etc/security/pam_winbind.conf

    [Global]
       debug = no
       debug_state = no
       try_first_pass = yes
       krb5_auth = yes
       krb5_ccache_type = FILE:/run/user/%u/krb5cc
       cached_login = yes
       silent = no
       mkhomedir = yes

For most services, it will be sufficient to modify only the `/etc/pam.d/system-auth` file. Any configuration for programs that do not include this file will also need to be modified directly. Create a backup of the `/etc/pam.d/system-auth` file and use the following configuration:

    /etc/pam.d/system-auth

    #%PAM-1.0

    auth       required                    pam_faillock.so      preauth
    # Optionally use requisite above if you do not want to prompt for the password
    # on locked accounts.
    -auth      [success=3 default=ignore]  pam_systemd_home.so
    auth       [success=2 default=ignore]  pam_winbind.so
    auth       [success=1 default=bad]     pam_unix.so          try_first_pass nullok
    auth       [default=die]               pam_faillock.so      authfail
    auth       optional                    pam_permit.so
    auth       required                    pam_env.so
    auth       required                    pam_faillock.so      authsucc
    # If you drop the above call to pam_faillock.so the lock will be done also
    # on non-consecutive authentication failures.

    -account   [success=2 default=ignore]  pam_systemd_home.so
    account    [success=1 default=ignore]  pam_winbind.so
    account    required                    pam_unix.so
    account    optional                    pam_permit.so
    account    required                    pam_time.so

    -password  [success=2 default=ignore]  pam_systemd_home.so
    password   [success=1 default=ignore]  pam_winbind.so
    password   required                    pam_unix.so          try_first_pass nullok shadow sha512
    password   optional                    pam_permit.so

    -session   optional                    pam_systemd_home.so
    session    required                    pam_mkhomedir.so skel=/etc/skel/ umask=0022
    session    required                    pam_limits.so
    session    required                    pam_winbind.so
    session    required                    pam_unix.so
    session    optional                    pam_permit.so

If you have other services that do not include the `/etc/pam.d/system-auth` file, modify the configuration to mirror all pam_unix.so entries for pam_winbind.so and change all required to sufficient. A good example is the su configuration. Create a backup of the `/etc/pam.d/su` file and use the following in its place:

    /etc/pam.d/su

    #%PAM-1.0

    auth      sufficient  pam_rootok.so
    # Uncomment the following line to implicitly trust users in the "wheel" group.
    #auth     required    pam_wheel.so   trust use_uid
    # Uncomment the following line to require a user to be in the "wheel" group.
    #auth     required    pam_wheel.so    use_uid
    auth      sufficient  pam_winbind.so
    auth      required    pam_unix.so
    account   sufficient  pam_winbind.so
    account   required    pam_unix.so
    session   sufficient  pam_winbind.so
    session   required    pam_unix.so

The above pam_winbind configuration will not use the default location of the Kerberos ticket (`KRB5CCNAME`), which is at `/tmp/krb5cc_UID`. Instead, it stores the automatically refreshed Kerberos ticket to `/run/user/UID/krb5cc`. Append the following to your krb5.conf to let Kerberos know your new location:

    /etc/krb5.conf

    [libdefaults]
       ...
       default_ccache_name = /run/user/%{uid}/krb5cc
       ...

To test your changes, start a new console or ssh session (do not exit your existing session until you have tested thoroughly) and try to login using the AD credentials. The domain name is optional, as this was set in the Winbind configuration as 'default realm'. Please note that in the case of ssh, you will need to modify the `/etc/ssh/sshd_config` file to allow kerberos authentication (see below).

Run klist to verify that you have received a kerberos ticket. You should see something similar to:

    $ klist

    Ticket cache: FILE:/run/user/20000/krb5cc
    Default principal: administrator@INTERNAL.DOMAIN.TLD

    Valid starting       Expires              Service principal
    12/25/2020 03:35:21  12/25/2020 13:35:21  krbtgt/INTERNAL.DOMAIN.TLD@INTERNAL.DOMAIN.TLD
            renew until 12/26/2020 03:35:15

Finally, you should test login as both the root user and a local unprivileged user before logging out of your existing (working) session.

## Old Wiki Article

Active Directory serves as a central location for network administration and security. It is responsible for authenticating and authorizing all users and computers within a Windows domain network, assigning and enforcing security policies for all computers in a network and installing or updating software on network computers. For example, when a user logs into a computer that is part of a Windows domain, it is Active Directory that verifies their password and specifies whether they are a system administrator or normal user. Server computers on which Active Directory is running are called domain controllers.

Active Directory uses Lightweight Directory Access Protocol (LDAP) versions 2 and 3, Microsoft's version of Kerberos and DNS.

### Terminology

If you are not familiar with Active Directory, there are a few keywords that are helpful to know.

- Domain : The name used to group computers and accounts.
- SID : Each computer that joins the domain as a member must have a unique SID or System Identifier.
- SMB : Server Message Block.
- NETBIOS: Network naming protocol used as an alternative to DNS. Mostly legacy, but still used in Windows Networking.
- WINS: Windows Information Naming Service. Used for resolving Netbios names to windows hosts.
- Winbind: Protocol for windows authentication.

### Active Directory configuration

This section works with the default configuration of Windows Server 2012 R2.

#### GPO considerations

Digital signing is enabled by default in Windows Server, and must be enabled at both the client and server level. For certain versions of Samba, Linux clients may experience issues connecting to the domain and/or shares. It is recommended you add the following parameters to your `smb.conf` file:

    client signing = auto
    server signing = auto

If that is not successful, you can disable Digital Sign Communication (Always) in the AD group policies. In your AD Group Policy editor, locate:

Under Local policies > Security policies > Microsoft Network Server > Digital sign communication (Always) activate define this policy and use the disable radio button.

If you use Windows Server 2008 R2, you need to modify that in GPO for Default Domain Controller Policy > Computer Setting > Policies > Windows Setting > Security Setting > Local Policies > Security Option > Microsoft network client: Digitally sign communications (always).

Please note that disabling this GPO affects the security of all members of the domain.

### Linux host configuration

The next few steps will begin the process of configuring the Host. You will need root or sudo access to complete these steps.

#### Installation

Install the following packages:

- samba, see also Samba
- pam-krb5
- ntp or openntpd, see also NTPd or OpenNTPD

#### Updating DNS

Active Directory is heavily dependent upon DNS. You will need to update `/etc/resolv.conf` to use one or more of the Active Directory domain controllers:

    /etc/resolv.conf

    nameserver <IP1>
    nameserver <IP2>

Replacing <IP1> and <IP2> with valid IP addresses for the AD servers. If your AD domains do not permit DNS forwarding or recursion, you may need to add additional resolvers.

Note

- The DNS entry 127.0.0.53 in the /etc/resolv.conf file refers to the local DNS resolver provided by systemd-resolved. If you have configured your DNS Servers using Network manager this step is unnecessary and can cause issues if you modify the resolv.conf as suggested.
- If your machine dual boots Windows and Linux, you should use a different DNS hostname and netbios name for the linux configuration if both operating systems will be members of the same domain.

#### Configuring NTP

Read System time#Time synchronization to configure an NTP service.

On the NTP servers configuration, use the IP addresses for the AD servers, as they typically run NTP as a service. Alternatively, you can use other known NTP servers provided the Active directory servers sync to the same stratum.

Ensure that the service is configured to sync the time automatically very early on startup.

#### Kerberos

Let us assume that your AD is named example.com. Let us further assume your AD is ruled by two domain controllers, the primary and secondary one, which are named PDC and BDC, pdc.example.com and bdc.example.com respectively. Their IP adresses will be 192.168.1.2 and 192.168.1.3 in this example. Take care to watch your syntax; upper-case is very important here.

    /etc/krb5.conf

    [libdefaults]
            default_realm 	= 	EXAMPLE.COM
    	clockskew 	= 	300
    	ticket_lifetime	=	1d
            forwardable     =       true
            proxiable       =       true
            dns_lookup_realm =      true
            dns_lookup_kdc  =       true

    [realms]
    	EXAMPLE.COM = {
    		kdc 	= 	PDC.EXAMPLE.COM
            kdc     =   PDC2.EXAMPLE.COM
            admin_server = PDC.EXAMPLE.COM
    		admin_server = PDC2.EXAMPLE.COM
            default_domain = EXAMPLE.COM
    	}

    [domain_realm]
            .kerberos.server = EXAMPLE.COM
    	.example.com = EXAMPLE.COM
    	example.com = EXAMPLE.COM
    	example	= EXAMPLE.COM

    [appdefaults]
    	pam = {
    	ticket_lifetime 	= 1d
    	renew_lifetime 		= 1d
    	forwardable 		= true
    	proxiable 		= false
    	retain_after_close 	= false
    	minimum_uid 		= 0
    	debug 			= false
    	}

    [logging]
    	default 		= FILE:/var/log/krb5libs.log
    	kdc 			= FILE:/var/log/kdc.log
            admin_server            = FILE:/var/log/kadmind.log

Note Heimdal 1.3.1 deprecated DES encryption which is required for AD authentication before Windows Server 2008. You will probably have to add

    allow_weak_crypto = true

to the `[libdefaults]` section.

##### Creating a Kerberos ticket

Note The keys and commands are user specific: sudo will be root, so your non-elevated account can connect to a different AD user with a separate key. If you only have one domain, it is not necessary to type @EXAMPLE.COM

Now you can query the AD domain controllers and request a kerberos ticket (uppercase is necessary):

    kinit administrator@EXAMPLE.COM

Note The suggested `smb.conf`, including `winbind use default domain = yes` cannot use `@EXAMPLE.COM` in the username. `kinit administrator` will bring in the `DOMAINNAME` from `smb.conf`.

You can use any username that has rights as a Domain Administrator.

##### Validating the Ticket

Run klist to verify you did receive the token. You should see something similar to:

    # klist

     Ticket cache: FILE:/tmp/krb5cc_0
     Default principal: administrator@EXAMPLE.COM

     Valid starting    Expires           Service principal
     02/04/12 21:27:47 02/05/12 07:27:42 krbtgt/EXAMPLE.COM@EXAMPLE.COM
             renew until 02/05/12 21:27:47

#### pam_winbind.conf

If you get errors stating that /etc/security/pam_winbind.conf was not found, create the file and add the following:

    /etc/security/pam_winbind.conf

    [global]
      debug = no
      debug_state = no
      try_first_pass = yes
      krb5_auth = yes
      krb5_ccache_type = FILE
      cached_login = yes
      silent = no
      mkhomedir = yes

With this setup, winbind will create user keytabs on the fly (krb5_ccache_type = FILE) at login and maintain them. You can verify this by simply running klist in a shell after logging in as an AD user but without needing to run kinit. You may need to set additional permissions on /etc/krb5.keytab eg 640 instead of 600 to get this to work (see FS#52621 for example)

#### Samba

Samba is a free software re-implementation of the SMB/CIFS networking protocol. It also includes tools for Linux machines to act as Windows networking servers and clients.

Note The configuration can vary greatly depending on how the Windows environment is deployed. Be prepared to troubleshoot and research

In this section, we will focus on getting Authentication to work first by editing the 'Global' section first. Later, we will go back and add shares.

    /etc/samba/smb.conf

    [Global]
      netbios name = MYARCHLINUX
      workgroup = EXAMPLE
      realm = EXAMPLE.COM
      server string = %h Arch Linux Host
      security = ads
      encrypt passwords = yes
      password server = pdc.example.com
      client signing = auto
      server signing = auto

      idmap config * : backend = tdb
      idmap config * : range = 10000-20000

      winbind use default domain = Yes
      winbind enum users = Yes
      winbind enum groups = Yes
      winbind nested groups = Yes
      winbind separator = +
      winbind refresh tickets = yes
      winbind offline logon = yes
      winbind cache time = 300

      template shell = /bin/bash
      template homedir = /home/%D/%U

      preferred master = no
      dns proxy = no
      wins server = pdc.example.com
      wins proxy = no

      inherit acls = Yes
      map acl inherit = Yes
      acl group control = yes

      load printers = no
      debug level = 3
      use sendfile = no

#### Join the domain

You need an AD Administrator account to do this. Let us assume this is named Administrator. The command is 'net ads join'

    # net ads join -U Administrator

    Administrator's password: xxx
    Using short domain name -- EXAMPLE
    Joined 'MYARCHLINUX' to realm 'EXAMPLE.COM'

### Starting and testing services

#### Starting Samba

Hopefully, you have not rebooted yet! Fine. If you are in an X-session, quit it, so you can test login into another console, while you are still logged in.

Enable and start the individual Samba daemons `smbd.service`, `nmbd.service`, and `winbindd.service`.

Note In samba 4.8.0-1, the Samba daemon units have been renamed from `smbd.service`, `nmbd.service`, and `winbindd.service` to `smb.service`, `nmb.service`, and `winbind.service`.

Next we will need to modify the NSSwitch configuration, which tells the Linux host how to retrieve information from various sources and in which order to do so. In this case, we are appending Active Directory as additional sources for Users, Groups, and Hosts.

    /etc/nsswitch.conf

     passwd:            files winbind
     shadow:            files winbind
     group:             files winbind

     hosts:             files dns wins

#### Testing Winbind

Let us check if winbind is able to query the AD. The following command should return a list of AD users:

    # wbinfo -u

    administrator
    guest
    krbtgt
    test.user

- Note we created an Active Directory user called 'test.user' on the domain controller

We can do the same for AD groups:

    # wbinfo -g

    domain computers
    domain controllers
    schema admins
    enterprise admins
    cert publishers
    domain admins
    domain users
    domain guests
    group policy creator owners
    ras and ias servers
    allowed rodc password replication group
    denied rodc password replication group
    read-only domain controllers
    enterprise read-only domain controllers
    dnsadmins
    dnsupdateproxy

#### Testing nsswitch

To ensure that our host is able to query the domain for users and groups, we test nsswitch settings by issuing the 'getent' command.

The following output shows what a stock Arch Linux install looks like:

    # getent passwd

    root:x:0:0:root:/root:/bin/bash
    bin:x:1:1:bin:/bin:/bin/false
    daemon:x:2:2:daemon:/sbin:/bin/false
    mail:x:8:12:mail:/var/spool/mail:/bin/false
    ftp:x:14:11:ftp:/srv/ftp:/bin/false
    http:x:33:33:http:/srv/http:/bin/false
    nobody:x:99:99:nobody:/:/bin/false
    dbus:x:81:81:System message bus:/:/bin/false
    ntp:x:87:87:Network Time Protocol:/var/empty:/bin/false
    avahi:x:84:84:avahi:/:/bin/false
    administrator:*:10001:10006:Administrator:/home/EXAMPLE/administrator:/bin/bash
    guest:*:10002:10007:Guest:/home/EXAMPLE/guest:/bin/bash
    krbtgt:*:10003:10006:krbtgt:/home/EXAMPLE/krbtgt:/bin/bash
    test.user:*:10000:10006:Test User:/home/EXAMPLE/test.user:/bin/bash

And for groups:

    # getent group

    root:x:0:root
    bin:x:1:root,bin,daemon
    daemon:x:2:root,bin,daemon
    sys:x:3:root,bin
    adm:x:4:root,daemon
    tty:x:5:
    disk:x:6:root
    lp:x:7:daemon
    mem:x:8:
    kmem:x:9:
    wheel:x:10:root
    ftp:x:11:
    mail:x:12:
    uucp:x:14:
    log:x:19:root
    utmp:x:20:
    locate:x:21:
    rfkill:x:24:
    smmsp:x:25:
    http:x:33:
    games:x:50:
    network:x:90:
    video:x:91:
    audio:x:92:
    optical:x:93:
    floppy:x:94:
    storage:x:95:
    scanner:x:96:
    power:x:98:
    nobody:x:99:
    users:x:100:
    dbus:x:81:
    ntp:x:87:
    avahi:x:84:
    domain computers:x:10008:
    domain controllers:x:10009:
    schema admins:x:10010:administrator
    enterprise admins:x:10011:administrator
    cert publishers:x:10012:
    domain admins:x:10013:test.user,administrator
    domain users:x:10006:
    domain guests:x:10007:
    group policy creator owners:x:10014:administrator
    ras and ias servers:x:10015:
    allowed rodc password replication group:x:10016:
    denied rodc password replication group:x:10017:krbtgt
    read-only domain controllers:x:10018:
    enterprise read-only domain controllers:x:10019:
    dnsadmins:x:10020:
    dnsupdateproxy:x:10021:

#### Testing Samba commands

Try out some net commands to see if Samba can communicate with AD:

    # net ads info

    [2012/02/05 20:21:36.473559,  0] param/loadparm.c:7599(lp_do_parameter)
      Ignoring unknown parameter "idmapd backend"
    LDAP server: 192.168.1.2
    LDAP server name: PDC.example.com
    Realm: EXAMPLE.COM
    Bind Path: dc=EXAMPLE,dc=COM
    LDAP port: 389
    Server time: Sun, 05 Feb 2012 20:21:33 CST
    KDC server: 192.168.1.2
    Server time offset: -3

    # net ads lookup

    [2012/02/05 20:22:39.298823,  0] param/loadparm.c:7599(lp_do_parameter)
      Ignoring unknown parameter "idmapd backend"
    Information for Domain Controller: 192.168.1.2

    Response Type: LOGON_SAM_LOGON_RESPONSE_EX
    GUID: 2a098512-4c9f-4fe4-ac22-8f9231fabbad
    Flags:
            Is a PDC:                                   yes
            Is a GC of the forest:                      yes
            Is an LDAP server:                          yes
            Supports DS:                                yes
            Is running a KDC:                           yes
            Is running time services:                   yes
            Is the closest DC:                          yes
            Is writable:                                yes
            Has a hardware clock:                       yes
            Is a non-domain NC serviced by LDAP server: no
            Is NT6 DC that has some secrets:            no
            Is NT6 DC that has all secrets:             yes
    Forest:                 example.com
    Domain:                 example.com
    Domain Controller:      PDC.example.com
    Pre-Win2k Domain:       EXAMPLE
    Pre-Win2k Hostname:     PDC
    Server Site Name :              Office
    Client Site Name :              Office
    NT Version: 5
    LMNT Token: ffff
    LM20 Token: ffff

    # net ads status -U administrator%password | less

    objectClass: top
    objectClass: person
    objectClass: organizationalPerson
    objectClass: user
    objectClass: computer
    cn: myarchlinux
    distinguishedName: CN=myarchlinux,CN=Computers,DC=leafscale,DC=inc
    instanceType: 4
    whenCreated: 20120206043413.0Z
    whenChanged: 20120206043414.0Z
    uSNCreated: 16556
    uSNChanged: 16563
    name: myarchlinux
    objectGUID: 2c24029c-8422-42b2-83b3-a255b9cb41b3
    userAccountControl: 69632
    badPwdCount: 0
    codePage: 0
    countryCode: 0
    badPasswordTime: 0
    lastLogoff: 0
    lastLogon: 129729780312632000
    localPolicyFlags: 0
    pwdLastSet: 129729764538848000
    primaryGroupID: 515
    objectSid: S-1-5-21-719106045-3766251393-3909931865-1105
    ...<snip>...

### Configuring PAM

Now we will change various rules in PAM to allow Active Directory users to use the system for things like login and sudo access. When changing the rules, note the order of these items and whether they are marked as required or sufficient is critical to things working as expected. You should not deviate from these rules unless you know how to write PAM rules.

In case of logins, PAM should first ask for AD accounts, and for local accounts if no matching AD account was found. Therefore, we add entries to include `pam_winbind.so` into the authentication process.

The Arch Linux PAM configuration keeps the central auth process in `/etc/pam.d/system-auth`. Starting with the stock configuration from `pambase`, change it like this:

#### system-auth

##### "auth" section

Find the line:

    auth required pam_unix.so ...

Delete it, and replace with:

    auth [success=1 default=ignore] pam_localuser.so
    auth [success=2 default=die] pam_winbind.so
    auth [success=1 default=die] pam_unix.so nullok
    auth requisite pam_deny.so

##### "account" section

Find the line:

    account required pam_unix.so

Keep it, and add this below:

    account [success=1 default=ignore] pam_localuser.so
    account required pam_winbind.so

##### "password" section

Find the line:

    password required pam_unix.so ...

Delete it, and replace with:

    password [success=1 default=ignore] pam_localuser.so
    password [success=2 default=die] pam_winbind.so
    password [success=1 default=die] pam_unix.so sha512 shadow
    password requisite pam_deny.so

##### "session" section

Find the line:

    session required pam_unix.so

Keep it, and add this line immediately above it:

    session required pam_mkhomedir.so skel=/etc/skel/ umask=0022

Below the pam_unix line, add these:

    session [success=1 default=ignore] pam_localuser.so
    session required pam_winbind.so

#### passwd

##### "password" section

In order for logged-in Active Directory users to be able to change their passwords with the 'passwd' command, the file `/etc/pam.d/passwd` must include the information from system-auth.

Find the line:

    password required pam_unix.so sha512 shadow nullok

Delete it, and replace with:

    password include system-auth

#### Testing login

Now, start a new console session (or ssh) and try to login using the AD credentials. The domain name is optional, as this was set in the Winbind configuration as 'default realm'. Please note that in the case of ssh, you will need to modify the `/etc/ssh/sshd_config` file to allow kerberos authentication `(KerberosAuthentication yes)`.

    test.user
    EXAMPLE+test.user

Both should work. You should notice that `/home/example/test.user` will be automatically created. Log into another session using an linux account. Check that you still be able to log in as root - but keep in mind to be logged in as root in at least one session!

### Configuring Shares

Earlier we skipped configuration of the shares. Now that things are working, go back to `/etc/samba/smb.conf`, and add the exports for the host that you want available on the windows network.

    /etc/samba/smb.conf

    [MyShare]
      comment = Example Share
      path = /srv/exports/myshare
      read only = no
      browseable = yes
      valid users = @NETWORK+"Domain Admins" NETWORK+test.user

In the above example, the keyword NETWORK is to be used. Do not mistakenly substitute this with your domain name. For adding groups, prepend the '@' symbol to the group. Note that `Domain Admins` is encapsulated in quotes so Samba correctly parses it when reading the configuration file.

### Adding a machine keytab file and activating password-free kerberized ssh to the machine

This explains how to generate a machine keytab file which you will need e.g. to enable password-free kerberized ssh to your machine from other machines in the domain. The scenario in mind is that you have a bunch of systems in your domain and you just added a server/workstation using the above description to your domain onto which a lot of users need to ssh in order to work - e.g. GPU workstation or an OpenMP compute node, etc. In this case you might not want to type your password every time you log in. On the other hand the key authentication used by many users in this case can not give you the necessary credentials to e.g. mount kerberized NFSv4 shares. So this will help you to enable password-free logins from your clients to the machine in question using kerberos ticket forwarding.

#### Creating a machine key tab file

run 'net ads keytab create -U administrator' as root to create a machine keytab file in /etc/krb5.keytab. It will prompt you with a warning that we need to enable keytab authentication in our configuration file, so we will do that in the next step. In my case it had problems when a key tab file is already in place - the command just did not come back it hang ... In that case you should rename the existing /etc/krb5.keytab and run the command again - it should work now.

    # net ads keytab create -U administrator

verify the content of your keytab by running:

    # klist -k /etc/krb5.keytab

    Keytab name: FILE:/etc/krb5.keytab
    KVNO Principal
    ---- --------------------------------------------------------------------------
       4 host/myarchlinux.example.com@EXAMPLE.COM
       4 host/myarchlinux.example.com@EXAMPLE.COM
       4 host/myarchlinux.example.com@EXAMPLE.COM
       4 host/myarchlinux.example.com@EXAMPLE.COM
       4 host/myarchlinux.example.com@EXAMPLE.COM
       4 host/MYARCHLINUX@EXAMPLE.COM
       4 host/MYARCHLINUX@EXAMPLE.COM
       4 host/MYARCHLINUX@EXAMPLE.COM
       4 host/MYARCHLINUX@EXAMPLE.COM
       4 host/MYARCHLINUX@EXAMPLE.COM
       4 MYARCHLINUX$@EXAMPLE.COM
       4 MYARCHLINUX$@EXAMPLE.COM
       4 MYARCHLINUX$@EXAMPLE.COM
       4 MYARCHLINUX$@EXAMPLE.COM
       4 MYARCHLINUX$@EXAMPLE.COM

#### Enabling keytab authentication

Now you need to tell winbind to use the file by adding these lines to the /etc/samba/smb.conf:

     kerberos method = secrets and keytab
     dedicated keytab file = /etc/krb5.keytab

It should look something like this:

    /etc/samba/smb.conf

    [Global]
      netbios name = MYARCHLINUX
      workgroup = EXAMPLE
      realm = EXAMPLE.COM
      server string = %h Arch Linux Host
      security = ads
      encrypt passwords = yes
      password server = pdc.example.com
      kerberos method = secrets and keytab
      dedicated keytab file = /etc/krb5.keytab

      idmap config * : backend = tdb
      idmap config * : range = 10000-20000

      winbind use default domain = Yes
      winbind enum users = Yes
      winbind enum groups = Yes
      winbind nested groups = Yes
      winbind separator = +
      winbind refresh tickets = yes

      template shell = /bin/bash
      template homedir = /home/%D/%U

      preferred master = no
      dns proxy = no
      wins server = pdc.example.com
      wins proxy = no

      inherit acls = Yes
      map acl inherit = Yes
      acl group control = yes

      load printers = no
      debug level = 3
      use sendfile = no

Restart the `winbindd.service`

Check if everything works by getting a machine ticket for your system by running

    # kinit MYARCHLINUX$ -kt /etc/krb5.keytab

This should not give you any feedback but running 'klist' should show you sth like:

    # klist

     Ticket cache: FILE:/tmp/krb5cc_0
     Default principal: MYARCHLINUX$@EXAMPLE.COM

     Valid starting    Expires           Service principal
     02/04/12 21:27:47 02/05/12 07:27:42 krbtgt/EXAMPLE.COM@EXAMPLE.COM
             renew until 02/05/12 21:27:47

Some common mistakes here are a) forgetting the trailing $ or b) ignoring case sensitivity - it needs to look exactly like the entry in the keytab (usually you cannot to much wrong with all capital)

#### Preparing sshd on server

All we need to do is add some options to our `sshd_config` and restart the `sshd.service`.

Edit `/etc/ssh/sshd_config` to look like this in the appropriate places:

    # /etc/ssh/sshd_config

    ...

    # Change to no to disable s/key passwords
    ChallengeResponseAuthentication no

    # Kerberos options
    KerberosAuthentication yes
    #KerberosOrLocalPasswd yes
    KerberosTicketCleanup yes
    KerberosGetAFSToken yes

    # GSSAPI options
    GSSAPIAuthentication yes
    GSSAPICleanupCredentials yes

    ...

Restart the `sshd.service`.

#### Adding necessary options on client

First we need to make sure that the tickets on our client are forwardable. This is usually standard but we better check anyways. You have to look for the forwardable option and set it to 'true' in the Kerberos configuration file `/etc/krb5.conf`

    forwardable     =       true

Secondly we need to add the options

     GSSAPIAuthentication yes
     GSSAPIDelegateCredentials yes

to our `.ssh/config` file to tell ssh to use this options - alternatively they can be invoked using the `-o` options directly in the ssh command (see ssh(1) for help).

#### Testing the setup

On Client:

make sure you have a valid ticket - if in doubt run 'kinit'

then use ssh to connect to you machine

    ssh myarchlinux.example.com

you should get connected without needing to enter your password.

if you have key authentication additionally activated then you should perform

    ssh -v myarchlinux.example.com

to see which authentication method it actually uses.

For debugging you can enable DEBUG3 on the server and look into the journal using journalctl.

#### Nifty fine-tuning for complete password-free kerberos handling.

In case your clients are not using domain accounts on their local machines (for whatever reason) it can be hard to actually teach them to kinit before ssh to the workstation. Therefore I came up with a nice workaround:

### Generating user Keytabs which are accepted by AD

On a system let the user run:

    ktutil
    addent -password -p username@EXAMPLE.COM -k 1 -e RC4-HMAC
    - enter password for username -
    wkt username.keytab
    q

Now test the file by invoking:

    kinit username@EXAMPLE.COM -kt username.keytab

It should not promt you to give your password nor should it give any other feedback. If it worked you are basically done - just put the line above into your ~./bashrc - you can now get kerberos tickets without typing a password and with that you can connect to your workstation without typing a password while being completely kerberized and able to authenticate against NFSv4 and CIFS via tickets - pretty neat.

#### Nice to know

The file 'username.keytab' is not machinespecific and can therefore be copied around. E.g. we created the files on a linux machine and copied them to our Mac clients as the commands on Macs are different ...

### További olvasnivaló a témában

- Wikipedia - Active Directory
- Wikipedia - Samba
- Wikipedia - Kerberos
- Samba - Documentation
- Directory on Samba Wiki
- Samba Wiki - Samba, Active Directory & LDAP
- smb.conf(5)

#### Using SSSD

sssd can be used instead of Samba to integrate with AD. See SSSD documentation.

#### Commercial solutions

- Centrify
- Likewise

#### OpenSource version

- PowerBroker Identity Services Open: formerly Likewise acquired by BeyondTrust
- Centrify Express for Linux

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