Join Linux Mint 19 to an Active Directory Domain

Created at 2019-01-10 Updated at 2020-06-10 Tag Linux Mint / Active Directory

TL;DR

Here are all the steps needed to add your Linux Mint computer to a Windows Active Directory Domain. For more detail, and explanation, please read The Rest of the Story.

$ sudo apt install realmd sssd sssd-tools libnss-sss libpam-sss krb5-user adcli samba-common-bin oddjob oddjob-mkhomedir packagekit samba python-dnspython

Restart your computer, then edit krb.conf.

$ sudo xed /etc/krb5.conf
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[libdefaults]
default_realm = AWESOME.COM
dns_lookup_kdc = true
dns_lookup_realm = true

[realms]
AWESOME.COM = {
kdc = awesome.com
admin_server = awesome.com
master_kdc = awesome.com
default_domain = awesome.com
}

[domain_realm]
.awesome.com = AWESOME.COM
awesome.com = AWESOME.COM

[logging]
kdc = SYSLOG:INFO
admin_server = FILE=/var/kadm5.log
$ sudo pam-auth-update

Edit realmd.conf.

$ sudo xed /etc/realmd.conf
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[users]
default-home = /home/%U
default-shell = /bin/bash

[active-directory]
default-client = sssd
os-name = Linux Mint
os-version = 19.1

[service]
automatic-install = no

[awesome.com]
fully-qualified-names = yes
automatic-id-mapping = no
user-principal = yes
manage-system = yes

Edit timesyncd.conf.

$ sudo xed /etc/systemd/timesyncd.conf
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[Time]
NTP=asmdc7.awesome.com
#FallbackNTP=ntp.ubuntu.com
#RootDistanceMaxSec=5
#PollIntervalMinSec=32
#PollIntervalMaxSec=2048
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$ sudo timedatectl set-ntp true
$ sudo systemctl restart systemd-timesyncd.service
$ sudo timedatectl --adjust-system-clock
$ timedatectl status

Discover the realm you want to join.

$ realm discover awesome.com

Test your credentials.

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$ kinit avawesome
$ klist
$ kdestroy

Join the Active Directory Domain.

$ sudo realm join --verbose --user=aawesome-a --computer-ou=OU=Computers,OU="ASM Headquarters",DC=awesome,DC=com awesome.com

Edit sssd.conf.

$ sudo xed /etc/sssd/sssd.conf
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[sssd]
domains = awesome.com
config_file_version = 2
services = nss, pam

[domain/awesome.com]
ad_domain = awesome.com
krb5_realm = AWESOME.COM
realmd_tags = manages-system joined-with-adcli
cache_credentials = True
id_provider = ad
krb5_store_password_if_offline = True
default_shell = /bin/bash
ldap_id_mapping = True
use_fully_qualified_names = True
fallback_homedir = /home/%u
access_provider = ad

Restart the SSSD Service.

$ sudo systemctl restart sssd.service

Finally, update your login screen.

Restart your computer, and you should able to log in using your Active Directory Credentials.

Update 8/30/2019: Click here to see some optional, final steps you could take.

The Rest of the Story

I work for a "Windows Shop", or ".Net Shop". Call it what you like, but it boils down to no Linux to be found. Fortunately, my work environment is flexible, so I decided to take on the challenge to put Linux only on my work laptop, and get it up and running.

Things like snaps have been extremely helpful in getting the software I need on my machine, and LibreOffice has come a long way. Everything else, like Office 365 for email, just needs a web browser. And in case I run into any edge cases, I do have Windows 10 on a VirtualBox image, but all that is outside of the scope of this article.

My very first step to tackle was Windows Active Directory Integration with a Linux machine; I needed to be able to use my Active Directory credentials to log into my Linux laptop.

Spoiler alert. I got it to work! :-) And I'm very excited to be able to use Linux at home and now at work!

Read on to see how I did it.

Steps Toward Awesome

First, I would like to give credit where credit is due. This article was extremely helpful in guiding me in getting everything set up.

Step 0: Install the Needed Packages

Open up your terminal, and enter the text below to get the needed packages installed.

$ sudo apt install realmd sssd sssd-tools libnss-sss libpam-sss krb5-user adcli samba-common-bin oddjob oddjob-mkhomedir packagekit samba python-dnspython

The krb5-user package will prompt for the Active Directory "realm", and you'll want to enter your realm in all CAPS.

After I installed the packages, I went ahead and restarted my machine.

Step 1: Edit Your krb5.conf File

Start by opening krb5.conf:

$ sudo xed /etc/krb5.conf

You can replace the contents of the current file with the text below.

Note: Values inside the double brackets (i.e. - [[value]]), need to be replaced with the correct values for your environment. Replace the value, and additionally, remove the double brackets. (i.e. - domain = [[my-domain.com]] –> domain = awesome.com)

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[libdefaults]
default_realm = [[YOUR-REALM.COM]] #YOUR-REALM.COM should be in CAPS
dns_lookup_kdc = true
dns_lookup_realm = true

[realms]
[[YOUR-REALM.COM]] = { #replace value, remove double brackets
kdc = [[your-realm.com]]
admin_server = [[your-realm.com]]
master_kdc = [[your-realm.com]]
default_domain = [[your-domain.com]] #my domain and realm were the same
}

[domain_realm]
.[[your-domain.com]] = [[YOUR-REALM.COM]] #YOUR-REALM.COM should be in CAPS
[[your-domain.com]] = [[YOUR-REALM.COM]]

[logging]
kdc = SYSLOG:INFO
admin_server = FILE=/var/kadm5.log

To finish up this step, run:

$ sudo pam-auth-update

Step 2: Edit Your realmd.conf File

Now open up your realmd.conf file.

$ sudo xed /etc/realmd.conf

Copy and paste the text below into the file. You can of course replace the values for "os-name" and "os-version".

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[users]
default-home = /home/%U
default-shell = /bin/bash

[active-directory]
default-client = sssd
os-name = [[Linux Mint]] #you can put your Linux Distribution Name
os-version = [[19.1]] #you can put your Distribution Version

[service]
automatic-install = no

[my-domain.com] #replace my-domain.com, but KEEP the brackets on this one
fully-qualified-names = yes
automatic-id-mapping = no
user-principal = yes
manage-system = yes

Step 3: Edit Your timesyncd.conf File

You should be used to editing files by now in this tutorial, so here we go again. Open up your terminal, and enter the text below.

$ sudo xed /etc/systemd/timesyncd.conf

All you need to do is change the "NTP" value to the address of your local Network Time Protocol (NTP) Server. You may have to ask your Network Administrator for the server address, and if you are the Network Administrator, I hope you know the address of your NTP Server ;-)

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[Time]
NTP=[[my-ntp-server.my-domain.com]] #replace value, remove double brackets
#FallbackNTP=ntp.ubuntu.com
#RootDistanceMaxSec=5
#PollIntervalMinSec=32
#PollIntervalMaxSec=2048

Now you'll need to update your local network time. Your local computer time needs to be within five minutes of the Kerberos (authentication) Server. So the clock times need to match, or you won't be able to log in.

You'll need to run the following commands in order to make sure your date and time are up-to-date.

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$ sudo timedatectl set-ntp true
$ sudo systemctl restart systemd-timesyncd.service
$ sudo timedatectl --adjust-system-clock

Now you can check the status of your local date and time synchronization.

$ timedatectl status

And your results should be similar to the screenshot below.

Step 4: Test Your Credentials

Even though your computer may not be bound to the Active Directory yet, you can now test your login credentials to make sure everything is set up correctly so far.

Run the command below.

$ realm discover [[my-domain.com]]

Successful results should look similar to the output below.

my-domain.com
type: kerberos
realm-name: MY-REALM.COM
domain-name: my-domain.com
configured: kerberos-member
server-software: active-directory
client-software: sssd
required-package: sssd-tools
required-package: sssd
required-package: libnss-sss
required-package: libpam-sss
required-package: adcli
required-package: samba-common-bin
login-formats: %U@my-domain.com
login-policy: allow-realm-logins

You can now try to "test" your login credentials. Do that by running the commands below, and enter your Active Directory password when prompted.

$ kinit [[my-user-name]]

You can verify that your login attempt worked by running this next command.

$ klist

If that worked, your results should look similar to the screenshot below.

Be sure to destroy your Kerberos token when you're done.

$ kdestroy

Step 5: Join the Active Directory Domain

Time to join your Active Directory. You'll need a Network Administrator, or someone with a Network Admin username/password in order to get your computer joined to the Active Directory realm.

Enter the text below into your terminal, and don't forget to replace the values in the double brackets (along with the brackets).

$ sudo realm join --verbose --user=[[network-admin-username]] --computer-ou=OU=[[Computers]],OU="[[Active-Directory-OU-Value]]",DC=[[my-domain-without-the-com]],DC=com [[my-domain.com]]

You'll enter the Network Administrator username, and you'll be prompted for the password.

 * Resolving: _ldap._tcp.my-domain.com
* Performing LDAP DSE lookup on: 10.1.1.14
* Performing LDAP DSE lookup on: 10.1.1.15
* Performing LDAP DSE lookup on: 10.1.1.28
* Successfully discovered: my-domain.com
Password for awesome-admin:

After the Network Administrator password has been entered, the rest of the output should look similar to this:

* Unconditionally checking packages
* Resolving required packages
* LANG=C /usr/sbin/adcli join --verbose --domain my-domain.com --domain-realm MY-REALM.COM --domain-controller 10.1.1.14 --computer-ou OU=Computers,OU=SHORT-DOMAIN-NAME Headquarters,DC=domain-controller,DC=com --os-name Linux Mint --os-version 19.1 --login-type user --login-user network-admin-username --stdin-password --user-principal
* Using domain name: my-domain.com
* Calculated computer account name from fqdn: COMPUTER-NAME
* Using domain realm: my-domain.com
* Sending netlogon pings to domain controller: cldap://10.1.1.14
* Received NetLogon info from: SERVER.my-domain.com
* Wrote out krb5.conf snippet to /var/cache/realmd/adcli-xyzab-oFOwIT/krb5.d/adcli-krb5-conf-wCGqIO
* Authenticated as user: network-admin-username@MY-REALM.COM
* Looked up short domain name: SHORT-DOMAIN-NAME
* Using fully qualified name: computer-name
* Using domain name: my-domain.com
* Using computer account name: COMPUTER-NAME
* Using domain realm: my-domain.com
* Calculated computer account name from fqdn: COMPUTER-NAME
* With user principal: host/computer-name@MY-REALM.COM
* Generated 120 character computer password
* Using keytab: FILE:/etc/krb5.keytab
* Found computer account for COMPUTER-NAME$ at: CN=COMPUTER-NAME,OU=Computers,OU=SHORT-DOMAIN-NAME Headquarters,DC=my-domain,DC=com
* Set computer password
* Retrieved kvno '7' for computer account in directory: CN=COMPUTER-NAME,OU=Computers,OU=SHORT-DOMAIN-NAME Headquarters,DC=my-domain,DC=com
* Modifying computer account: userAccountControl
* Modifying computer account: operatingSystemVersion, operatingSystemServicePack
* Modifying computer account: userPrincipalName
* Discovered which keytab salt to use
* Added the entries to the keytab: COMPUTER-NAME$@MY-REALM.COM: FILE:/etc/krb5.keytab
* Added the entries to the keytab: host/COMPUTER-NAME@MY-REALM.COM: FILE:/etc/krb5.keytab
* Added the entries to the keytab: host/COMPUTER-NAME@MY-REALM.COM: FILE:/etc/krb5.keytab
* Cleared old entries from keytab: FILE:/etc/krb5.keytab
* Added the entries to the keytab: host/computer-name@MY-REALM.COM: FILE:/etc/krb5.keytab
* Added the entries to the keytab: RestrictedKrbHost/COMPUTER-NAME@MY-REALM.COM: FILE:/etc/krb5.keytab
* Added the entries to the keytab: RestrictedKrbHost/computer-name@MY-REALM.COM: FILE:/etc/krb5.keytab
* /usr/sbin/update-rc.d sssd enable
* /usr/sbin/service sssd restart
* Successfully enrolled machine in realm

Step 6: Edit Your sssd.conf File

Open up sssd.conf for editing

$ sudo xed /etc/sssd/sssd.conf

Copy and paste the text below into the file. Again, don't forget to replace the values in the double brackets (along with the brackets).

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[sssd]
domains = [[my-domain]].com
config_file_version = 2
services = nss, pam

[domain/[[my-domain]].com]
ad_domain = [[my-domain]].com
krb5_realm = [[MY-REALM]].COM
realmd_tags = manages-system joined-with-adcli
cache_credentials = True
id_provider = ad
krb5_store_password_if_offline = True
default_shell = /bin/bash
ldap_id_mapping = True
use_fully_qualified_names = True
fallback_homedir = /home/%u
access_provider = ad

Save the file, then close the text editor, and run the command below.

$ sudo systemctl restart sssd.service

Step 7: Modify Your Login Window

And now for our last step. This is specific for Linux Mint.

Start by opening the Login Window settings, as seen in the screenshot below.

Now make sure you settings look like this:

Conclusion

Those are the steps. If anything is unclear, let me know in the comments below. Hope this is helpful :-)

Update 8/30/2019

So this is an optional step that may not have to happen in every scenario. Upon logging in with your Active Directory User, you may discover that you do not have the rights to do anything. So, you will have to log in with a local administrator account, and add your domain account to the following groups by running these commands:

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$ sudo usermod -a -G adm aaronvon@awesome.com
$ sudo usermod -a -G cdrom aaronvon@awesome.com
$ sudo usermod -a -G dip aaronvon@awesome.com
$ sudo usermod -a -G lpadmin aaronvon@awesome.com
$ sudo usermod -a -G plugdev aaronvon@awesome.com
$ sudo usermod -a -G sambashare aaronvon@awesome.com
$ sudo usermod -a -G sudo aaronvon@awesome.com

End of Line.

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