Join an Active Directory Domain

Pop!_OS and Ubuntu can be joined to an Active Directory domain, which allows users to log in with their existing network credentials.

Install the necessary packages:
```
 sudo apt install sssd heimdal-clients msktutil
```
While installing those packages, you will be prompted for the following information. These are sample responses. Our domain is called “system76.local” and our Active Directory server is called “adserver” in this example:
```
 Forest name: SYSTEM76
 Domain controller hostname: ADSERVER.system76.local
 Administrative server for your Kerberos realm: ADSERVER.system76.local
```

Move the default Kerberos configuration file to a backup, and create a fresh file to use:

 sudo mv /etc/krb5.conf /etc/krb5.conf.default
 sudo nano /etc/krb5.conf

Edit the /etc/krb5.conf file with the following contents:

 [libdefaults]
 default_realm = SYSTEM76.LOCAL
 rdns = no
 dns_lookup_kdc = true
 dns_lookup_realm = true

 [realms]
 SYSTEM76.LOCAL = {
 kdc = ADSERVER.system76.local
 admin_server = ADSERVER.system76.local
 }

Initialize Kerberos and generate a keytab file. The first command requires the username of a domain administrator, and our computer’s hostname is “pop-os” in this example:

 kinit administrator
 klist
 msktutil -N -c -b 'CN=COMPUTERS' -s POP-OS/pop-os.system76.local -k my-keytab.keytab ‑‑computer-name POP-OS ‑‑upn POP-OS$ ‑‑server adserver.system76.local ‑‑user-creds-only
 msktutil -N -c -b 'CN=COMPUTERS' -s POP-OS/pop-os -k my-keytab.keytab ‑‑computer-name POP-OS ‑‑upn POP-OS$ ‑‑server adserver.system76.local ‑‑user-creds-only
 kdestroy

Move the keytab to the /etc/sssd directory, and configure SSSD:

 sudo mv my-keytab.keytab /etc/sssd/my-keytab.keytab
 sudo nano /etc/sssd/sssd.conf 

The SSSD configuration file should contain the following:

 [sssd]
 services = nss, pam
 config_file_version = 2
 domains = system76.local

 [nss]
 entry_negative_timeout = 0
 #debug_level = 5

 [pam]
 #debug_level = 5

 [domain/system76.local]
 #debug_level = 10
 enumerate = false
 id_provider = ad
 auth_provider = ad
 chpass_provider = ad
 access_provider = ad
 dyndns_update = false
 ad_hostname = pop-os.system76.local
 ad_server = adserver.system76.local
 ad_domain = system76.local
 ldap_schema = ad
 ldap_id_mapping = true
 fallback_homedir = /home/%u
 default_shell = /bin/bash
 ldap_sasl_mech = gssapi
 ldap_sasl_authid = POP-OS$
 krb5_keytab = /etc/sssd/my-keytab.keytab
 ldap_krb5_init_creds = true

After saving, set the appropriate permissions on that configuration file:

 sudo chmod 0600 /etc/sssd/sssd.conf

Configure PAM:
```
 sudo nano /etc/pam.d/common-session
```
Look for the line that contains “session required pam_unix.so” and add this line immediately below it:
```
 session required pam_mkhomedir.so skel=/etc/skel umask=0077
```
After saving that file, restart SSSD:
```
 sudo systemctl restart sssd 
```
Add the domain administrator to the local sudo group:
```
 sudo adduser administrator sudo
```
Then, test a login with the domain administrator:
```
 su -l administrator
```
Reboot the computer. At the login screen, you can click the “Not listed?” link, and type the username of any domain user. After logging in with a domain user for the first time, that user will appear on the login screen’s user list.