Linux machine in a Windows AD domain using sssd and krb5

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Tutorial

There was a need to introduce a Ubuntu machine into the Windows domain. For these purposes, Samba and Winbind are commonly used. But an alternative is possible with sssd, a brief guide to it below.

For example, we will use:

Domain = contoso.com
Domain Controller = dc.contoso.com

Start the Ubuntu terminal:

1. Switch to root

sudo -i

2. Install the necessary packages

apt install sssd heimdal-clients msktutil

3. Edit /etc/krb5.conf, use tabs as indents.

[libdefaults]
	default_realm = CONTOSO.COM
[realms]
	CONTOSO.COM = {
		kdc = DC 
		admin_server = dc.contoso.com
		default_domain = contoso.com
	}
[login]
	krb4_convert = true
	krb4_get_tickets = false
[domain_realm]
        .contoso.com = CONTOSO.COM
        contoso.com = CONTOSO.COM

4. Edit the / etc / hosts file, specify the FQDN for this host:

127.0.0.1       localhost
127.0.1.1       <hostname>.contoso.com  <hostname>

5. We try to get the Kerberos ticket on behalf of the domain administrator:

root@ubuntu:~# kinit YourDomainAdmin
YourDomainAdmin@CONTOSO.COM's Password:

Checking:

root@ubuntu:~# klist
Credentials cache: FILE:/tmp/krb5cc_0
        Principal: YourDomainAdmin@CONTOSO.COM
  Issued                Expires               Principal
Dec  1 15:08:27 2018  Dec  2 01:08:22 2018  krbtgt/CONTOSO.COM@CONTOSO.COM

If the ticket is received successfully, then now Kerberos principals can be generated for this host, the register is important:

msktutil -c -b 'CN=YourComputersOU' -s HOST/HOSTNAME.contoso.com -k /etc/sssd/HOSTNAME.keytab --computer-name HOSTNAME --upn HOSTNAME$ --server dc.contoso.com —user-creds-only
msktutil -c -b 'CN=YourComputersOU' -s HOST/HOSTNAME -k /etc/sssd/HOSTNAME.keytab --computer-name HOSTNAME --upn HOSTNAME$ --server dc.contoso.com --user-creds-only

Now our host should appear in the list of computers in the directory. If everything is so, we delete the received Kerberos ticket:

kdestroy

6. Create the file /etc/sssd/sssd.conf with the following contents:

[sssd]
services = nss, pam
config_file_version = 2
domains = contoso.com
[nss]
entry_negative_timeout = 0
debug_level = 3
[pam]
debug_level = 3
[domain/contoso.com]
debug_level = 3
ad_domain = contoso.com
ad_server = dc.contoso.com
enumerate = false
id_provider = ad
auth_provider = ad
chpass_provider = ad
access_provider = simple
simple_allow_groups = users #каким группам разрешено логиниться, через запятую. Есть ограничение — названия групп должны быть с маленькой буквы.
ldap_schema = ad
ldap_id_mapping = true
fallback_homedir = /home/%u
default_shell = /bin/bash
ldap_sasl_mech = gssapi
ldap_sasl_authid = <HOSTNAME>$
ldap_krb5_init_creds = true
krb5_keytab = /etc/sssd/<HOSTNAME>.keytab

The description of the sssd configuration parameters can be found here.

Set permissions for the sssd.conf file:

chmod 600 /etc/sssd/sssd.conf

Restart the SSSD service

service sssd restart

7. Edit the PAM settings.

Bad solution:

edit the /etc/pam.d/common-session file, after the line

session required        pam_unix.so

add row

session required pam_mkhomedir.so skel=/etc/skel umask=0022

A good solution:

redefine the parameters through the PAM system settings, call

pam-auth-update

and mark sss auth and makehomdir . This will automatically add the
line above in common-session and it will not be overloaded when the system is updated.

Now we can log in to the machine by domain users who are allowed to login.

PS: You can give the right to use sudo domain groups. Using visudo, edit the file / etc / sudoers, or better, as recommended by maxzhurkin and iluvar , create a new file in /etc/sudoers.d/ and edit it

visudo -f /etc/sudoers.d/ваш_файл

Add the required group - for example, Domain Admins (if there are spaces in the group name, they must be escaped):

%Domain\ Admins ALL=(ALL) ALL

PSS: Thanks gotch for the info about realmd. Very convenient - if you do not need specific settings, then entering the machine into the domain takes, in fact, three commands:
1. Install the necessary packages:

sudo apt install realmd samba-common-bin samba-libs sssd-tools krb5-user adcli

2. Check that our domain is visible on the network:

realm discover contoso.com

3. Enter the machine in the domain:

sudo realm --verbose join contoso.com -U YourDomainAdmin

4. Edit PAM settings

sudo pam-auth-update

An additional advantage of this option is pass-through authorization on domain file resources.

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Linux machine in a Windows AD domain using sssd and krb5

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