how to setup Bind in CentOS 5

BIND is an open-source software that implements the Domain Name System (DNS) protocols for the Internet. The name BIND stands for “Berkeley Internet Name Domain”. This article describes how to install and configure BIND in Red Hat Enterprise Linux 5 or CentOS 5.

Installing BIND

The steps below will install the chrooted BIND and the GUI configuration tool.

1. Type in the command below to install BIND.

yum install bind-chroot system-config-bind

2. Start the named service. Learn how to start and stop services.

3. Open the TCP port 53 and UDP port 53. Learn how to configure the firewall.

Configuring BIND

The steps shows how to configure BIND using the GUI configuration tool.

1. Click System, select Administration and click Domain Name System. This will launch the BIND Configuration GUI window.

2. Click Ok to initialize BIND with default values.

3. BIND has now been initialized. We can now create a DNS zone and add DNS records.

Creating a DNS Zone

The steps below will show you how to create a DNS zone named “acme.local”.

1. To create a DNS zone, right click DNS Server, select Add and click Zone.

2. In the New Zone window, click the Ok button under Class.

3. Next, click the Ok button under Origin Type.

4. Provide the name of the zone and click Ok.

5. Review the various settings and click Ok.

6. Click Save and click Yes.

7. You now have a new DNS zone.

Creating DNS Records

The steps below describes how to create some of the most common DNS records.

Creating an A record

An A record maps a hostname to its IPv4 address.

1. Right click the zone you where you want to add an A record, select Add and click A IPv4 Address.

2. Specify the Domain Name and IPv4 Address and click Ok.

3. Click Save and click Yes.

Creating a CNAME record

A CNAME record specifies that a domain name is an alias of another domain name.

1. Right click the zone you where you want to add a CNAME record, select Add and click CNAME Alias.

2. Specify the Domain Name and Canonical Name (target domain name) and click Ok.

3. Click Save and click Yes.

Creating an MX record

An MX record specifies how Internet e-mail should be routed using SMTP.

1. Right click the zone you where you want to add an MX record, select Add and click MX Mail Exchange.

2. Specify the Mail Server Name and click Ok.

3. Click Save and click Yes.

Testing BIND

To test your BIND setup, you can use the nslookup and dig utility.

1. Type the command below in a terminal window to use nslookup

nslookup mail.acme.local localhost

Replace mail.acme.local with the domain you want to check. If your DNS server is not on localhost then change it.

2. Type in the command below to query any records using dig.

dig @localhost acme.local ANY

Replace acme.local with your own domain. If your DNS server is not on localhost then change it.

Samba Server Types and the smb.conf File

Samba configuration is straightforward. All modifications to Samba are done in the /etc/samba/smb.conf configuration file. Although the default smb.conf file is well documented, it does not address complex topics such as LDAP, Active Directory, and the numerous domain controller implementations.

The following sections describe the different ways a Samba server can be configured. Keep in mind your needs and the changes required to the smb.conf file for a successful configuration.

Stand-alone Server

A stand-alone server can be a workgroup server or a member of a workgroup environment. A stand-alone server is not a domain controller and does not participate in a domain in any way. The following examples include several anonymous share-level security configurations and one user-level security configuration.

Anonymous Read-Only

The following smb.conf file shows a sample configuration needed to implement anonymous read-only file sharing. The security = share parameter makes a share anonymous. Note, security levels for a single Samba server cannot be mixed. The security directive is a global Samba parameter located in the [global] configuration section of the smb.conf file.

[global]
workgroup = DOCS
netbios name = DOCS_SRV
security = share 
[data]
comment = Documentation Samba Server
path = /export
read only = Yes
guest only = Yes

Anonymous Read/Write

The following smb.conf file shows a sample configuration needed to implement anonymous read/write file sharing. To enable anonymous read/write file sharing, set the read only directive to no. The force user and force group directives are also added to enforce the ownership of any newly placed files specified in the share.

Note

Although having an anonymous read/write server is possible, it is not recommended. Any files placed in the share space, regardless of user, are assigned the user/group combination as specified by a generic user (force user) and group (force group) in the smb.conf file.

[global]
workgroup = DOCS
netbios name = DOCS_SRV
security = share 
[data]
comment = Data
path = /export
force user = docsbot
force group = users
read only = No
guest ok = Yes

Anonymous Print Server

The following smb.conf file shows a sample configuration needed to implement an anonymous print server. Setting browseable to no as shown does not list the printer in Windows Network Neighborhood. Although hidden from browsing, configuring the printer explicitly is possible. By connecting to DOCS_SRV using NetBIOS, the client can have access to the printer if the client is also part of the DOCS workgroup. It is also assumed that the client has the correct local printer driver installed, as the use client driver directive is set to Yes. In this case, the Samba server has no responsibility for sharing printer drivers to the client.

[global]
workgroup = DOCS
netbios name = DOCS_SRV
security = share
printcap name = cups
disable spools= Yes
show add printer wizard = No
printing = cups 
[printers]
comment = All Printers
path = /var/spool/samba
guest ok = Yes
printable = Yes
use client driver = Yes
browseable = Yes

Secure Read/Write File and Print Server

The following smb.conf file shows a sample configuration needed to implement a secure read/write print server. Setting the security directive to user forces Samba to authenticate client connections. Notice the [homes] share does not have a force user or force group directive as the [public] share does. The [homes] share uses the authenticated user details for any files created as opposed to the force user and force group in [public].

[global]
workgroup = DOCS
netbios name = DOCS_SRV
security = user
printcap name = cups
disable spools = Yes
show add printer wizard = No
printing = cups 
[homes]
comment = Home Directories
valid users = %S
read only = No
browseable = No 
[public]
comment = Data
path = /export
force user = docsbot
force group = users
guest ok = Yes 
[printers]
comment = All Printers
path = /var/spool/samba
printer admin = john, ed, @admins
create mask = 0600
guest ok = Yes
printable = Yes
use client driver = Yes
browseable = Yes

Domain Member Server

A domain member, while similar to a stand-alone server, is logged into a domain controller (either Windows or Samba) and is subject to the domain's security rules. An example of a domain member server would be a departmental server running Samba that has a machine account on the Primary Domain Controller (PDC). All of the department's clients still authenticate with the PDC, and desktop profiles and all network policy files are included. The difference is that the departmental server has the ability to control printer and network shares.

Active Directory Domain Member Server

The following smb.conf file shows a sample configuration needed to implement an Active Directory domain member server. In this example, Samba authenticates users for services being run locally but is also a client of the Active Directory. Ensure that your kerberos realm parameter is shown in all caps (for example realm = EXAMPLE.COM). Since Windows 2000/2003 requires Kerberos for Active Directory authentication, the realm directive is required. If Active Directory and Kerberos are running on different servers, the password server directive may be required to help the distinction.

[global]
realm = EXAMPLE.COM
security = ADS
encrypt passwords = yes
# Optional. Use only if Samba cannot determine the Kerberos server automatically.
password server = kerberos.example.com

In order to join a member server to an Active Directory domain, the following steps must be completed:

• Configuration of the smb.conf file on the member server

• Configuration of Kerberos, including the /etc/krb5.conf file, on the member server

• Creation of the machine account on the Active Directory domain server

• Association of the member server to the Active Directory domain

To create the machine account and join the Windows 2000/2003 Active Directory, Kerberos must first be initialized for the member server wishing to join the Active Directory domain. To create an administrative Kerberos ticket, type the following command as root on the member server:

kinit administrator@EXAMPLE.COM

The kinit command is a Kerberos initialization script that references the Active Directory administrator account and Kerberos realm. Since Active Directory requires Kerberos tickets, kinit obtains and caches a Kerberos ticket-granting ticket for client/server authentication. For more information on Kerberos, the /etc/krb5.conf file, and the kinit command, refer to Section 42.6, “Kerberos”.

To join an Active Directory server (windows1.example.com), type the following command as root on the member server:

net ads join -S windows1.example.com -U administrator%password

Since the machine windows1 was automatically found in the corresponding Kerberos realm (the kinit command succeeded), the net command connects to the Active Directory server using its required administrator account and password. This creates the appropriate machine account on the Active Directory and grants permissions to the Samba domain member server to join the domain.

Note

Since security = ads and not security = user is used, a local password backend such as smbpasswd is not needed. Older clients that do not support security = ads are authenticated as if security = domain had been set. This change does not affect functionality and allows local users not previously in the domain.

Windows NT4-based Domain Member Server

The following smb.conf file shows a sample configuration needed to implement a Windows NT4-based domain member server. Becoming a member server of an NT4-based domain is similar to connecting to an Active Directory. The main difference is NT4-based domains do not use Kerberos in their authentication method, making the smb.conf file simpler. In this instance, the Samba member server functions as a pass through to the NT4-based domain server.

[global]
workgroup = DOCS
netbios name = DOCS_SRV
security = domain 
[homes]
comment = Home Directories
valid users = %S
read only = No
browseable = No 
[public]
comment = Data
path = /export
force user = docsbot
force group = users
guest ok = Yes

Having Samba as a domain member server can be useful in many situations. There are times where the Samba server can have other uses besides file and printer sharing. It may be beneficial to make Samba a domain member server in instances where Linux-only applications are required for use in the domain environment. Administrators appreciate keeping track of all machines in the domain, even if not Windows-based. In the event the Windows-based server hardware is deprecated, it is quite easy to modify the smb.conf file to convert the server to a Samba-based PDC. If Windows NT-based servers are upgraded to Windows 2000/2003, the smb.conf file is easily modifiable to incorporate the infrastructure change to Active Directory if needed.

Important

After configuring the smb.conf file, join the domain before starting Samba by typing the following command as root:

net rpc join -U administrator%password

Note that the -S option, which specifies the domain server hostname, does not need to be stated in the net rpc join command. Samba uses the hostname specified by the workgroup directive in the smb.conf file instead of it being stated explicitly.

Domain Controller

A domain controller in Windows NT is functionally similar to a Network Information Service (NIS) server in a Linux environment. Domain controllers and NIS servers both host user/group information databases as well as related services. Domain controllers are mainly used for security, including the authentication of users accessing domain resources. The service that maintains the user/group database integrity is called the Security Account Manager (SAM). The SAM database is stored differently between Windows and Linux Samba-based systems, therefore SAM replication cannot be achieved and platforms cannot be mixed in a PDC/BDC environment.

In a Samba environment, there can be only one PDC and zero or more BDCs.

Important

Samba cannot exist in a mixed Samba/Windows domain controller environment (Samba cannot be a BDC of a Windows PDC or vice versa). Alternatively, Samba PDCs and BDCs can coexist.

Primary Domain Controller (PDC) using tdbsam

The simplest and most common implementation of a Samba PDC uses the tdbsam password database backend. The passdb backend directive controls which backend is to be used for the PDC.

[global]
workgroup = DOCS
netbios name = DOCS_SRV 
passdb backend = tdbsam
security = user
add user script = /usr/sbin/useradd -m %u
delete user script = /usr/sbin/userdel -r %u
add group script = /usr/sbin/groupadd %g 
delete group script = /usr/sbin/groupdel %g 
add user to group script = /usr/sbin/usermod -G %g %u
add machine script = /usr/sbin/useradd -s /bin/false -d /dev/null  -g machines %u
# The following specifies the default logon script 
# Per user logon scripts can be specified in the user
# account using pdbedit logon script = logon.bat
# This sets the default profile path.
# Set per user paths with pdbedit
logon drive = H:
domain logons = Yes
os level = 35
preferred master = Yes
domain master = Yes 
[homes]
 comment = Home Directories
 valid users = %S
 read only = No 
[netlogon]
 comment = Network Logon Service
 path = /var/lib/samba/netlogon/scripts
 browseable = No 
 read only = No
# For profiles to work, create a user directory under the
# path shown.
mkdir -p /var/lib/samba/profiles/john
[Profiles]
 comment = Roaming Profile Share
 path = /var/lib/samba/profiles
 read only = No
 browseable = No
 guest ok = Yes
 profile acls = Yes 
# Other resource shares ... ...

Update CentOS 5.0 to 5.1

To update CentOS 5.0 to CentOS 5.1, all you have to do is type in yum update from the Terminal window. This command will automatically get the updated packages over the internet. But if you have the CentOS 5.1 DVD, the steps below will show you how to update from that.

1. Insert the CentOS 5.1 DVD into the DVD drive and double click the Computer icon in the CentOS Desktop.

2. On the Computer – File Browser window, double click on the CD-ROM Drive.

3. The CentOS 5.1 DVD should now be available on /media/CentOS_5.1_Final.

4. From a terminal window, type in ln -sf /media/CentOS_5.1_Final /media/CentOS and press Enter. This enables the CentOS 5.1 DVD to be located on the yum search path.

5. Edit the file /etc/yum.repos.d/CentOS-Media.repo and change beta into CentOS-5 in the line gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-beta.

6. Finally, type in yum --disablerepo=* --enablerepo=c5-media and press Enter to begin the update process.

For 64-bit users: You need to add the line login_process_size = 64 in the file /etc/dovecot.conf and restart dovecot after upgrading.

how to administer a Red Hat Enterprise Linux 5 or CentOS 5 server.

System Management

This section describes how to perform system management tasks.

How to add, edit or remove a user account

How to add or remove packages or applications

How to start, stop or restart a background service
How to enable or disable an on demand service

How to configure the firewall

How to synchronize the system clock using NTP

System Utilities

This section describes utilities you can use to manage your system.

How to setup SSH to remotely administer a Linux server using a command line

How to use VNC to remotely administer a Linux server using a GUI

How to setup Webmin, a web based system administration tool

How to use rsync to synchronize files between two computers

How to use vi, a command line editor

How to Setup Webmin in CentOS 5

1.Go to www.webmin.com and download the Webmin RPM package.

2. Double click the downloaded file to install Webmin.

3. After installing Webmin, configure the firewall to allow traffic on the TCP port 10000. Learn how to configure the firewall.

4. Start the httpd service. Learn how to start and stop services here.

5. From a web browser, connect to https://localhost:10000 and login using root.

6. That’s it. It’s working.

Webmin is a web-based interface for system administration for Unix. Using any modern web browser, you can setup user accounts, Apache, DNS, file sharing and much more. This article will show you how to install Webmin.

Setup and Configure LDAP User Information

It is recommended to an Active Directory enabled DNS server, this will ensure that the LDAP lookups and Kerberos authentication will work properly. Also, provide a user account dedicated for the LDAP authentication.

1. Click System, select Administration and click Authentication. This will launch the Authentication Configuration window.

2. Check Enable LDAP Support and click the Configure LDAP button.

3. Fill in the LDAP Search Base DN and LDAP Server fields. Click Ok when you are done.

4. Click the Options tab and check Local authorization is sufficient for local users and Create home directories on the first login. Click Ok when you are done.

4. Edit the file /etc/ldap.conf and add the following lines below.

binddn user account
bindpw password for binddn
nss_map_objectclass posixAccount User
nss_map_objectclass posixGroup Group
nss_map_attribute homeDirectory unixHomeDirectory

If you are using Services for Unix 3.5, remove the homeDirectory mapping above and add the lines below.

nss_map_attribute uid msSFU30Name
nss_map_attribute uidNumber msSFU30UidNumber
nss_map_attribute gidNumber msSFU30GidNumber
nss_map_attribute homeDirectory msSFU30HomeDirectory
nss_map_attribute loginShell msSFU30LoginShell

If you are not using an Active Directory enabled DNS server, you need to add the line referrals no to make this work.

5. Type in getent passwd in a terminal window. You should see your Active Directory user accounts.

6. Type in getent group in a terminal window. You should see your Active Directory groups.