CertPrep

The LPIC-3 300: Mixed Environment exam validates the ability to integrate Linux systems into heterogeneous networks with Unix, Windows, and directory services. This guide covers each exam objective with configuration examples, commands, and troubleshooting approaches.

Samba Architecture and Components

Samba provides file and print services to SMB/CIFS clients using four core daemons:

| Daemon | Purpose | | ----------- | ------------------------------------------------------ | | smbd | SMB/CIFS file and print service (TCP 139, 445) | | nmbd | NetBIOS name service and browsing (UDP 137, 138) | | winbindd | Authentication and identity resolution from AD or LDAP | | samba-ad-dc | Active Directory Domain Controller service |

smb.conf Structure

The main Samba configuration file is /etc/samba/smb.conf with two main sections:

[global]
   workgroup = MYDOMAIN
   server string = File Server %v
   netbios name = FILESRV
   security = user
   map to guest = Bad User
   log file = /var/log/samba/%m.log
   max log size = 50

[shared]
   comment = Shared Documents
   path = /srv/samba/shared
   browseable = yes
   read only = no
   guest ok = no
   valid users = @staff
   create mask = 0664
   directory mask = 0775

Samba Security Modes

| Mode | Description | | ------ | ------------------------------------------------------------- | | user | Users authenticate with local Samba user accounts (smbpasswd) | | domain | Samba authenticates against a legacy Windows NT domain PDC | | ads | Samba joins an Active Directory domain using Kerberos | | share | No authentication (deprecated, use map to guest instead) |

Joining Active Directory

# Install packages
apt-get install samba smbclient winbind libnss-winbind libpam-winbind

# Configure /etc/samba/smb.conf
[global]
   security = ads
   realm = AD.CORP.EXAMPLE.COM
   workgroup = AD
   netbios name = LINUXSRV

# Join the domain
net ads join -U Administrator

# Verify
net ads testjoin
wbinfo -u  # List domain users
wbinfo -g  # List domain groups

LDAP with OpenLDAP

OpenLDAP provides a centralized directory service for user authentication, address books, and configuration data.

slapd Configuration

Modern OpenLDAP uses the config backend (cn=config) for online configuration:

# Install
apt-get install slapd ldap-utils

# After initial configuration, view the config
ldapsearch -Y EXTERNAL -H ldapi:/// -b cn=config

LDAP Database Backends

| Backend | Description | | ------- | ---------------------------------------------------------------------- | | mdb | Memory-Mapped DB — recommended, high performance, no size limit | | bdb | Berkeley DB — deprecated, not recommended for new deployments | | hdb | Hierarchical BD — deprecated variant with entry-level subtree renaming | | ldif | Store entries as LDIF files — for testing only |

LDIF Entry Example

dn: uid=jdoe,ou=people,dc=example,dc=com
objectClass: inetOrgPerson
objectClass: posixAccount
objectClass: shadowAccount
uid: jdoe
cn: John Doe
sn: Doe
uidNumber: 1001
gidNumber: 100
homeDirectory: /home/jdoe
loginShell: /bin/bash
userPassword: {SSHA}encryptedhash
shadowLastChange: 19000

LDAP Search Filters

| Operator | Meaning | Example | | -------- | ---------------- | ----------------------------------------------------------- | | = | Equality | (uid=jdoe) | | >= | Greater or equal | (uidNumber>=1000) | | <= | Less or equal | (uidNumber<=2000) | | =* | Present | (mail=*) | | ~= | Approximate | (sn~=John) | | & | AND | (&(objectClass=posixAccount)(uidNumber>=1000)) | | \| | OR | (\|(objectClass=posixAccount)(objectClass=shadowAccount)) | | ! | NOT | (!(uid=root)) |

LDAP Access Control

ACLs in slapd.conf (or via olcAccess in cn=config):

dn: olcDatabase={1}mdb,cn=config
changetype: modify
add: olcAccess
olcAccess: to attrs=userPassword
  by self write
  by anonymous auth
  by * none
olcAccess: to *
  by self write
  by users read
  by * none

Kerberos

krb5.conf Structure

[libdefaults]
   default_realm = AD.CORP.EXAMPLE.COM
   dns_lookup_realm = true
   dns_lookup_kdc = true
   ticket_lifetime = 24h
   renew_lifetime = 7d
   forwardable = true

[realms]
   AD.CORP.EXAMPLE.COM = {
      kdc = dc01.ad.corp.example.com
      kdc = dc02.ad.corp.example.com
      admin_server = dc01.ad.corp.example.com
   }

[domain_realm]
   .ad.corp.example.com = AD.CORP.EXAMPLE.COM
   ad.corp.example.com = AD.CORP.EXAMPLE.COM

Key Commands

# Obtain a ticket
kinit administrator@AD.CORP.EXAMPLE.COM

# List cached tickets
klist

# Destroy tickets
kdestroy

# Create a keytab for a service
ktutil
ktutil: addent -password -p HTTP/srv01.ad.corp.example.com@AD.CORP.EXAMPLE.COM -k 1 -e aes256-cts-hmac-sha1-96
ktutil: wkt /etc/httpd.keytab
ktutil: quit

# Verify keytab
klist -kte /etc/httpd.keytab

Kerberized Services Configuration

For a web server using Kerberos authentication:

<Location /secure>
   AuthType Kerberos
   AuthName "Kerberos Login"
   KrbAuthRealms AD.CORP.EXAMPLE.COM
   KrbServicePrincipal HTTP/srv01.ad.corp.example.com
   Krb5KeyTab /etc/httpd.keytab
   KrbMethodNegotiate On
   Require valid-user
</Location>

Winbind Integration

Winbind resolves Windows user and group identities on Linux systems by querying AD via LDAP and Kerberos.

/etc/nsswitch.conf

passwd:         compat winbind
group:          compat winbind
shadow:         compat winbind

Winbind Configuration in smb.conf

[global]
   idmap config * : backend = tdb
   idmap config * : range = 3000-7999
   idmap config AD : backend = rid
   idmap config AD : range = 10000-999999
   winbind use default domain = yes
   winbind offline logon = yes
   winbind enum users = no
   winbind enum groups = no
   template shell = /bin/bash
   template homedir = /home/%U

NFSv4 in Mixed Environments

NFSv4 provides Kerberos-based authentication for cross-platform file sharing:

# Server side (/etc/exports)
/srv/nfs4  gss/krb5p(rw,sec=krb5p)

# Enable NFSv4 with Kerberos
nfsconf --set nfsd rdma no
nfsconf --set nfsd vers4.2 y
nfsconf --set nfsd vers4.0 y
nfsconf --set gssd use-gss-proxy y

# Client mount
mount -t nfs4 -o sec=krb5p server.example.com:/srv/nfs4 /mnt/nfs

PAM Configuration for Network Authentication

For PAM to use LDAP or Winbind authentication, the pam_ldap or pam_winbind module is configured:

# /etc/pam.d/common-auth
auth    [success=1 default=ignore]  pam_winbind.so
auth    requisite                   pam_deny.so
auth    required                    pam_permit.so
auth    optional                    pam_cap.so

Troubleshooting

Samba Debugging

# Test configuration
testparm

# Check SMB connectivity
smbclient -L //localhost -U%

# Query domain controllers
net ads info

# Test authentication
ntlm_auth --username=jdoe --domain=AD

LDAP Troubleshooting

# Check slapd status
slaptest -v

# Query with debugging
ldapsearch -d 1 -x -H ldap://localhost -b dc=example,dc=com

# Check ACLs
ldapsearch -Y EXTERNAL -H ldapi:/// -b cn=config olcAccess

Kerberos Troubleshooting

# Verbose authentication
KRB5_TRACE=/dev/stderr kinit user@REALM

# Check time synchronization (critical for Kerberos)
chronyc sources

# Test DNS SRV records
dig -t SRV _kerberos._tcp.ad.corp.example.com
dig -t SRV _ldap._tcp.ad.corp.example.com

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