Last week, I needed to setup a file server at work. Most of our back office server run Ubuntu except a few Microsoft Active Directory (AD) servers which control our workstations and user accounts. We make sure all of our Linux hosted services integrate with AD via Kerberos and LDAP.
Samba has been able to integrate with AD via winbind for a few years now. There are numerous postings on the net about how to do this. All of them a just a little different and many are a just a touch out of date for various distributions. Here's what I used to get an Ubuntu 9.10 server connected with our Microsoft Windows domain.
ACL Instructions
The normal install of Ubuntu and Debian support the standard Linux POSIX file system permissions. Access Control Lists (ACLs) provide a much more flexible way of specifying permissions on a file or other object than the standard Unix user/group/owner system. A good example you might deal with in production is the need to have "Domain Admins" and "HR" groups have write permission on a folder but the "Domain Users" only should have read access. That's not easy to do with standard POSIX.
Install the acl package:
sudo apt-get install acl
Now edit the partition that will hold your Samba shares so that it mounts with acl enabled. I typically create my shares in the /home/shares folder with my /home being mounted on its own volume.
vim /etc/fstab
Example:
/dev/mapper/vg0-home /home ext4 acl,defaults 0 2
Please be careful when editing your fstab file. It's a good idea to make a backup of it first especially if you are making changes to the / "root" mount.
Some recommend a reboot at this point but you don't have to if you execute the following remount command.
mount -o remount,rw /dev/mapper/vg0-home
Kerberos Instructions
Install the kerberos packages:
sudo apt-get install ntp krb5-config krb5-user
The package installer will prompt you for Kerberos server information. Don't worry about those just enter something to satisfy it. You are going to replace the cumbersome default krb5.conf with a specific one for Active Directory authentication.
If you already have samba and winbind daemons installed an running, stop them now.
sudo service samba stop
sudo service winbind stop
Now let's setup the Kerberos configuration for authentication with Active Directory.
sudo mv /etc/krb5.conf /etc/krb5.orig
sudo vim /etc/krb5.conf
Copy the following text. Make sure to change
SCHOOL.UNIVERSITY.EDU to your domain. Keep it in CAPS, though.
## /etc/krb5.conf
[logging]
default = FILE:/var/log/krb5.log
kdc = FILE:/var/log/krb5kdc.log
admin_server = FILE:/var/log/kadmin.log
[libdefaults]
default_realm = SCHOOL.UNIVERSITY.EDU
dns_lookup_realm = false
dns_lookup_kdc = false
clock_skew = 300
ticket_lifetime = 24h
forwardable = yes
[realms]
SCHOOL.UNIVERSITY.EDU = {
kdc = AD-CONTROLER1.SCHOOL.UNIVERSITY.EDU
kdc = AD-CONTROLER2.SCHOOL.UNIVERSITY.EDU
admin_server = AD-CONTROLER1.SCHOOL.UNIVERSITY.EDU
default_domain = SCHOOL.UNIVERSITY.EDU
}
[domain_realm]
.school.university.edu = SCHOOL.UNIVERSITY.EDU
.SCHOOL.UNIVERSITY.EDU = SCHOOL.UNIVERSITY.EDU
Note: In my example above, I've listed a secondary Kerberos server for authentication should the first domain controller be unavailable. You can add as many secondary kdc as you want. Remove this line if you only have one AD server.
Test to make sure the Kerberos connection before proceeding. This can save you some troubleshooting headaches later on.
kinit Administrator@SCHOOL.UNIVERSITY.EDU
The command should return clean and using klist should report a valid ticket good for 24 hours.
klist
Now you can setup the Samba configuration.
Samba smb.conf for Active Directory
The default Samba config file is verbose with comments and easy to make a mistake. It is better just to make a backup copy of it and create a clean configuration.
sudo mv /etc/samba/smb.conf /etc/samba/smb.orig
sudo /etc/samba/smb.conf
There are almost countless examples on the net about how to configure you Samba file. Everyone's got a slightly different setup. I've settled on the following for production use.
Note: You will want to make sure to change
SCHOOL.UNIVERSITY.EDU with your domain name.
[global]
dos charset = UTF8
display charset = UTF8
workgroup = SCHOOL
realm = SCHOOL.UNIVERSITY.EDU
server string = %h
security = ADS
map to guest = Bad User
null passwords = Yes
obey pam restrictions = Yes
pam password change = Yes
password server = AD-CONTROLER1.SCHOOL.UNIVERSITY.EDU
username map = /etc/samba/smbusers
max log size = 10
log file = /var/log/samba/log.%m
unix extensions = No
deadtime = 10
socket options = TCP_NODELAY SO_KEEPALIVE SO_SNDBUF=65536 SO_RCVBUF=65536
load printers = No
disable spoolss = Yes
dns proxy = No
idmap uid = 10000-20000
idmap gid = 10000-20000
template shell = /bin/bash
winbind separator = +
winbind cache time = 3600
winbind enum users = Yes
winbind enum groups = Yes
winbind refresh ticket = Yes
create mask = 0777
directory mask = 0777
use sendfile = Yes
delete veto files = Yes
veto files = /.AppleDB/.AppleDouble/.AppleDesktop/:2eDS_Store/Network Trash Folder/Temporary It
map hidden = Yes
map system = Yes
[HR]
comment = School HR Server Share
path = /home/shares/HR
read only = No
create mask = 0775
valid users = @"HR-Dept"
Some key notes about this configuration:
- socket options - The TCP_NODELAY makes noticeable improvement on file transfer speeds especially if you are using 1G NICs.
- obey pam restrictions - This integrates your PAM authentication system.
- veto files - Got Macs on your network? Keep those pesky .Apple file droppings off of your file server
- valid users - Only members of the HR-Dept user group will have access to the HR file share.
Restart the Samba and Winbind services.
sudo /etc/init.d/winbind stop
sudo /etc/init.d/samba restart
sudo /etc/init.d/winbind start
Now you can join the Samba server to the Active Directory Domain.
sudo net ads join -U Administrator
You should see a message that the target domain was joined successfully.
Testing & Troubleshooting
Check you domain membership with the wbinfo -t command. This will validate that workstation trust account is working correctly:
sudo wbinfo -t
You should see your domain users with this command:
sudo wbinfo -u
The -g option should list your domain's groups.
sudo wbinfo -g
Configure System Security
Now modify the /etc/nsswitch.conf file so the system can start recognising your domain accounts.
vim /etc/nsswitch.conf
Append winbind after compat for passwd and group. Leave everything else alone.
passwd: compat winbind
group: compat winbind
shadow: compat
hosts: files mdns4_minimal [NOTFOUND=return] dns mdns4
networks: files
protocols: db files
services: db files
ethers: db files
rpc: db files
Edit these PAM config files.
sudo mv /etc/pam.d/common-account /etc/pam.d/common-account.orig
sudo vim /etc/pam.d/common-account
Copy the following.
account sufficient pam_winbind.so
account required pam_unix.so
Now edit the common-auth file.
sudo cp /etc/pam.d/common-auth /etc/pam.d/common-auth.orig
sudo vim /etc/pam.d/common-auth
Now create a common-auth that looks like this
#
# /etc/pam.d/common-auth - authentication settings common to all services
#
# This file is included from other service-specific PAM config files,
# and should contain a list of the authentication modules that define
# the central authentication scheme for use on the system
# (e.g., /etc/shadow, LDAP, Kerberos, etc.). The default is to use the
# traditional Unix authentication mechanisms.
#
# As of pam 1.0.1-6, this file is managed by pam-auth-update by default.
# To take advantage of this, it is recommended that you configure any
# local modules either before or after the default block, and use
# pam-auth-update to manage selection of other modules. See
# pam-auth-update(8) for details.
# here are the per-package modules (the "Primary" block)
auth [success=3 default=ignore] pam_winbind.so krb5_auth krb5_ccache_type=FILE
auth [success=2 default=ignore] pam_krb5.so minimum_uid=1000
auth [success=1 default=ignore] pam_unix.so nullok_secure try_first_pass
# here's the fallback if no module succeeds
auth requisite pam_deny.so
# prime the stack with a positive return value if there isn't one already;
# this avoids us returning an error just because nothing sets a success code
# since the modules above will each just jump around
auth required pam_permit.so
# and here are more per-package modules (the "Additional" block)
# end of pam-auth-update config
Setup the pam common-session file so new users to the system get created with a standard skel profile and home directory
sudo cp /etc/pam.d/common-session /etc/pam.d/common-session.orig
sudo vim /etc/pam.d/common-session
Your common-session should look like this:
#
# /etc/pam.d/common-session - session-related modules common to all services
#
# This file is included from other service-specific PAM config files,
# and should contain a list of modules that define tasks to be performed
# at the start and end of sessions of *any* kind (both interactive and
# non-interactive).
#
# As of pam 1.0.1-6, this file is managed by pam-auth-update by default.
# To take advantage of this, it is recommended that you configure any
# local modules either before or after the default block, and use
# pam-auth-update to manage selection of other modules. See
# pam-auth-update(8) for details.
# here are the per-package modules (the "Primary" block)
session [default=1] pam_permit.so
# here's the fallback if no module succeeds
session requisite pam_deny.so
# prime the stack with a positive return value if there isn't one already;
# this avoids us returning an error just because nothing sets a success code
# since the modules above will each just jump around
session required pam_permit.so
# and here are more per-package modules (the "Additional" block)
session optional pam_krb5.so minimum_uid=1000
session required pam_unix.so
session required pam_mkhomedir.so umask=0022 skel=/etc/skel
# end of pam-auth-update config
Sudo'ers file
You can grant domain administrators elevated sudo permissions on the server by adding this line to your sudo configuration.
Open the sudo safe editor
sudo visudo
Add the following to the configuration:
# Allow "Domain Admins" from the domain "DOMAIN" to run all commands
%SCHOOL+Domain\ Admins ALL=(ALL) ALL
You will want to replace
SCHOOL with your domain name.
References
ACLs on Samba by Dustin Puryear
Join Samba 3 to Your Active Directory Domain - Carla Schroder
Active Directory Winbind Howto - Ubuntu Community Documentation
