Authenticating UNIX/Linux to Windows 2008R2. Part 4 : RHEL 6.0

Background

Continuation of setting up LDAP/Kerberos clients to use Windows 2008R2 Server as the “source of truth”.

See the previous blog , for the steps for how Windows was set up.

Installation of RHEL6.0

      1. Create a Red Hat Linux 6 Kickstart configuration:
        install
        text
        reboot
        cdrom
        lang en_US.UTF-8
        keyboard us
        network --device eth0 --bootproto dhcp
        rootpw password
        firewall --disabled
        authconfig --enableshadow --passalgo=sha512 --enablefingerprint
        selinux --disabled
        timezone --utc Australia/Melbourne
        bootloader --location=mbr --driveorder=sda --append="crashkernel=auto crashkernel=auto rhgb quiet"
        clearpart --all --initlabel --drives=sda
        part /boot --fstype ext4 --size=500 --ondisk=sda
        part pv.1 --grow --size=1 --ondisk=sda
        volgroup vg_rhel6 --pesize=4096 pv.1
        logvol / --fstype ext4 --name=lv_root --vgname=vg_rhel6 --grow -size=1024
        logvol swap --name=lv_swap --vgname=vg_rhel6 --grow --size=1024 --maxsize=2048
        %packages
        @Base
        @Core
        @base
        openldap-clients
        sssd
        sssd-client
        krb5-workstation
      2. Save this file on a VFAT/FAT floppy disk as ks.cfg
      3. Create a Red Hat Linux 5 x64 VM, with the following configuration:
        1. Custom Config, VMware Workstation 6.5 compatible
        2. I will install the operating system later.
        3. Guest OS : Linux, Red Hat Enterprise Linux 5 64-bit (RHEL6 not listed yet)
        4. VM Name: “rhel6host1”
        5. 1 Processor, 1 Core per Processor
        6. 1024MB Memory
        7. Use Host-Only Networking
        8. IDE Controller type: ATAPI
        9. SCSI Controller type: LSI Logic
        10. Disk: Create a new virtual disk, SCSI, Maximum Disk size, 10GB, Store as Single File, rhel6host1.vmdk (on an NTFS filesystem).
        11. Insert the Red Hat installer CD (Red Hat 5 Update 6)
        12. Power on and Boot from CD.
        13. Enter the following command line arguments:
          linux ks=floppy://ks.cfg
        14. Install VMware Tools:
          # mount -o ro /dev/cdrom /mnt
          # cp /mnt/VMware* /tmp
          # umount /mnt
          # cd /tmp
          # tar xfz VMware*
          # cd vmware-tools-distrib
          # ./vmware-install.pl -d
          # vmware-toolbox-cmd timesync enable
          Enabled
        15. Reconfigure the VM to use static IP addresses, and set the hostname, and DNS parameters
          # system-config-network-tui
          # service network restart

Plan of attack (in order):

        1. Get ldapsearch working with simple bind, unencrypted
        2. Configure LDAP with sssd
        3. Verify LDAP works with getent(1), id(1), etc
        4. Export the Root CA cert from Windows to UNIX
        5. Check the CA cert works with OpenSSL
        6. Import the CA cert
        7. Get LDAPS working with ldapsearch
        8. Change sssd to use LDAPS rather than LDAP
        9. Verify Kerberos works: Initially, without a host principal (krb5.keytab)
        10. Configure SSS to use Kerberos (edit /etc/sssd/sssd.conf)
        11. Configure PAM to use SSS
        12. Verify that services like login can use kerberised IDs and that the password works
        13. Create a host principal keytab in Windows. Import it into UNIX.
        14. Verify that kinit -k works
        15. Edit /etc/krb5/krb5.conf to include “verify_ap_req_nofail = true” in the [libdefaults] section. This will secure the UNIX box to prove it is talking with the bonefide KDC.
        16. Get Single-Sign-On working

1. Ldapsearch, unencrypted

ldapsearch on Linux is very similar but not identical to Solaris. Some of the command line options are subtly different. (eg the -x flag is required to use simple authentication, and URIs are supported)

Using the simple bind user, verify that lookups can be done using unencrypted LDAP. Not only will this return a record, but will also give the correct attribute name:

# ldapsearch -v -x -H ldap://adserver -D "CN=ldapsearch,CN=Users,DC=example,DC=com" \
-b "DC=example,DC=com" -w ld@p53arch -s sub "cn=unix1"
ldap_initialize( ldap://adserver )
filter: cn=unix1
requesting: All userApplication attributes
# extended LDIF
#
# LDAPv3
# base <DC=example,DC=com> with scope subtree
# filter: cn=unix1
# requesting: ALL
#

# unix1, UNIX, example.com
dn: CN=unix1,OU=UNIX,DC=example,DC=com
objectClass: top
objectClass: person
objectClass: organizationalPerson
objectClass: user
cn: unix1
distinguishedName: CN=unix1,OU=UNIX,DC=example,DC=com
instanceType: 4
whenCreated: 20110809102742.0Z
whenChanged: 20110810132335.0Z
uSNCreated: 20816
memberOf: CN=unixgrp1,OU=UNIX,DC=example,DC=com
uSNChanged: 21194
name: unix1
objectGUID:: 8dUSWOctkEaf5x7FkpXrgw==
userAccountControl: 512
badPwdCount: 0
codePage: 0
countryCode: 0
badPasswordTime: 129574586131856092
lastLogoff: 0
lastLogon: 129574589801917979
pwdLastSet: 129574562159321288
primaryGroupID: 513
objectSid:: AQUAAAAAAAUVAAAA9P+gsh3KJO48P5XaUAQAAA==
accountExpires: 9223372036854775807
logonCount: 72
sAMAccountName: unix1
sAMAccountType: 805306368
userPrincipalName: unix1@example.com
objectCategory: CN=Person,CN=Schema,CN=Configuration,DC=example,DC=com
dSCorePropagationData: 16010101000000.0Z
lastLogonTimestamp: 129574227701101793
uid: unix1
msSFU30Name: unix1
msSFU30NisDomain: example
uidNumber: 10000
gidNumber: 10000
unixHomeDirectory: /home/unix1
loginShell: /bin/sh

# search reference
ref: ldap://ForestDnsZones.example.com/DC=ForestDnsZones,DC=example,DC=com

# search reference
ref: ldap://DomainDnsZones.example.com/DC=DomainDnsZones,DC=example,DC=com

# search reference
ref: ldap://example.com/CN=Configuration,DC=example,DC=com

# search result
search: 2
result: 0 Success

# numResponses: 5
# numEntries: 1
# numReferences: 3

2. Configure LDAP with sssd, unencrypted

In RHEL 6, sssd is used to configure LDAP. For now, disable the auth_provider until LDAP is working. NB. With this, I have been unable to get secondary groups to work.

/etc/sss/sssd.conf:

[sssd]
config_file_version = 2
reconnection_retries = 3
sbus_timeout = 30
services = nss, pam
domains = EXAMPLE.COM

[nss]
filter_groups = root
filter_users = root
reconnection_retries = 3

[pam]
reconnection_retries = 3

[domain/EXAMPLE.COM]
description = LDAP domain with AD server
enumerate = false
min_id = 1
id_provider = ldap
;;;; auth_provider = krb5
ldap_uri = ldap://adserver.example.com/
ldap_schema = rfc2307bis
ldap_user_search_base = dc=example,dc=com
ldap_group_search_base = dc=example,dc=com
ldap_default_bind_dn = CN=ldapsearch,CN=Users,DC=example,DC=com
ldap_default_authtok_type = password
ldap_default_authtok = ld@p53arch

ldap_user_object_class = user
ldap_user_name = sAMAccountName
ldap_user_uid_number = uidNumber
ldap_user_gid_number = gidNumber
ldap_user_home_directory = unixHomeDirectory
ldap_user_shell = loginShell
ldap_user_principal = userPrincipalName
ldap_user_member = msSFU30PosixMemberOf

ldap_group_object_class = group
ldap_group_name = sAMAccountName
ldap_group_gid_number = gidNumber
ldap_group_member = memberUid

; THIS IS REQUIRED, BECAUSE BY DEFAULT IN WINDOWS, THE REALM NAME IS LOWERCASE
ldap_force_upper_case_realm = true

2. Configure /etc/nsswitch.conf

The following lines should be changed to use sss after files:

passwd:     files sss
shadow:     files sss
group:      files sss

3. Verify getent(1) works

Now, Lookups should work:

# service sssd start # getent group unixgrp1
unixgrp1:*:10000:unix1
# getent passwd unix1
unix1:*:10000:10000:unix1:/home/unix1:/bin/sh
# id -a unix1
uid=10000(unix1) gid=10000(unixgrp1) groups=10000(unixgrp1)

4. Import the root CA Certificates

The .PEM format rootCA.cer file should be copied (probably with psftp.exe) to the RedHat system. For the purposes of this instruction it is saved in /root/rootCA.cer.

5. Verify that the certificate file is ok with OpenSSL

# openssl x509 -in /root/rootCA.cer -subject -issuer -purpose
subject= /DC=com/DC=example/CN=example-ADSERVER-CA
issuer= /DC=com/DC=example/CN=example-ADSERVER-CA
Certificate purposes:
SSL client : Yes
SSL client CA : Yes
SSL server : Yes
SSL server CA : Yes
Netscape SSL server : No
Netscape SSL server CA : Yes
S/MIME signing : Yes
S/MIME signing CA : Yes
S/MIME encryption : No
S/MIME encryption CA : Yes
CRL signing : Yes
CRL signing CA : Yes
Any Purpose : Yes
Any Purpose CA : Yes
OCSP helper : Yes
OCSP helper CA : Yes
-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----

The CA root certificate can be tested as follows:

# openssl s_client -connect adserver.example.com:636 -CAfile /etc/openldap/cacerts/rootCA.cer  < /dev/null
CONNECTED(00000003)
depth=1 /DC=com/DC=example/CN=example-ADSERVER-CA
verify return:1
depth=0 /CN=adserver.example.com
verify return:1
---
Certificate chain
 0 s:/CN=adserver.example.com
   i:/DC=com/DC=example/CN=example-ADSERVER-CA
---
Server certificate
-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----
subject=/CN=adserver.example.com
issuer=/DC=com/DC=example/CN=example-ADSERVER-CA
---
Acceptable client certificate CA names
/DC=com/DC=example/CN=example-ADSERVER-CA
/CN=adserver.example.com
/C=US/O=VeriSign, Inc./OU=Class 3 Public Primary Certification Authority
/OU=Copyright (c) 1997 Microsoft Corp./OU=Microsoft Corporation/CN=Microsoft Root Authority
/DC=com/DC=microsoft/CN=Microsoft Root Certificate Authority
/CN=NT AUTHORITY
---
SSL handshake has read 2140 bytes and written 459 bytes
---
New, TLSv1/SSLv3, Cipher is AES128-SHA
Server public key is 2048 bit
Secure Renegotiation IS NOT supported
Compression: NONE
Expansion: NONE
SSL-Session:
    Protocol  : TLSv1
    Cipher    : AES128-SHA
    Session-ID: 0908000095B93DAB72C80378CB4A9A87C116CBFA47B3046953BDC5D0A123FBF9
    Session-ID-ctx:
    Master-Key: 605B7D5B698F92AE6350A8D98A9FFFBB3C19688060100C899F6447F097B2BEB132687079F0D05092612F462E458EDCA8
    Key-Arg   : None
    Krb5 Principal: None
    Start Time: 1313109018
    Timeout   : 300 (sec)
    Verify return code: 0 (ok)
---
DONE

6. Import the Root CA Certificate

The certificate should be copied into /etc/openldap/cacerts:

# cp /root/rootCA.cer /etc/openldap/cacerts
# cacertdir_rehash /etc/openldap/cacerts

7. Test ldapsearch works  with LDAPS

This line must be present in /etc/openldap/ldap.conf:

TLS_CACERTDIR /etc/openldap/cacerts

Now LDAPS searches can be performed:

# ldapsearch -v -x -H ldaps://adserver.example.com/ \
-D "CN=ldapsearch,CN=Users,DC=example,DC=com" -b "DC=example,DC=com" \
-w ld@p53arch -s sub "cn=unix1"
ldap_initialize( ldaps://adserver.example.com/ )
filter: cn=unix1
requesting: All userApplication attributes
# extended LDIF
#
# LDAPv3
# base <DC=example,DC=com> with scope subtree
# filter: cn=unix1
# requesting: ALL
#

# unix1, UNIX, example.com
dn: CN=unix1,OU=UNIX,DC=example,DC=com
objectClass: top
objectClass: person
objectClass: organizationalPerson
objectClass: user
cn: unix1
distinguishedName: CN=unix1,OU=UNIX,DC=example,DC=com
instanceType: 4
whenCreated: 20110809102742.0Z
whenChanged: 20110810132335.0Z
uSNCreated: 20816
memberOf: CN=unixgrp1,OU=UNIX,DC=example,DC=com
uSNChanged: 21194
name: unix1
objectGUID:: 8dUSWOctkEaf5x7FkpXrgw==
userAccountControl: 512
badPwdCount: 0
codePage: 0
countryCode: 0
badPasswordTime: 129574586131856092
lastLogoff: 0
lastLogon: 129574589801917979
pwdLastSet: 129574562159321288
primaryGroupID: 513
objectSid:: AQUAAAAAAAUVAAAA9P+gsh3KJO48P5XaUAQAAA==
accountExpires: 9223372036854775807
logonCount: 72
sAMAccountName: unix1
sAMAccountType: 805306368
userPrincipalName: unix1@example.com
objectCategory: CN=Person,CN=Schema,CN=Configuration,DC=example,DC=com
dSCorePropagationData: 16010101000000.0Z
lastLogonTimestamp: 129574227701101793
uid: unix1
msSFU30Name: unix1
msSFU30NisDomain: example
uidNumber: 10000
gidNumber: 10000
unixHomeDirectory: /home/unix1
loginShell: /bin/sh

# search reference
ref: ldaps://ForestDnsZones.example.com/DC=ForestDnsZones,DC=example,DC=com

# search reference
ref: ldaps://DomainDnsZones.example.com/DC=DomainDnsZones,DC=example,DC=com

# search reference
ref: ldaps://example.com/CN=Configuration,DC=example,DC=com

# search result
search: 2
result: 0 Success

# numResponses: 5
# numEntries: 1
# numReferences: 3
#

NB. Fully qualified host names must be used, since those names are in ther certifcate. Short host names won’t work:

# ldapsearch -v -x -H ldaps://adserver/ \
-D "CN=ldapsearch,CN=Users,DC=example,DC=com" -b "DC=example,DC=com" \
-w ld@p53arch -s sub "cn=unix1"
ldap_initialize( ldaps://adserver:636/??base )
ldap_sasl_bind(SIMPLE): Can't contact LDAP server (-1)

8. Change /etc/sss/sssd.conf to use LDAPS rather than LDAP

We already know that LDAP works. We need to change the mechanism from simple to simple over TLS. Again we also must be careful to use the FQDN:

Change/Add these lines:

ldap_uri = ldaps://adserver.example.com/
tls_cacertdir = /etc/openldap/cacerts
ldap_tls_reqcert = demand

Restart SSSD:

# # service sssd restart Stopping sssd:                                             [  OK  ] Starting sssd:                                             [  OK  ] 

We can verify that lookups are now working:

# getent passwd unix1
unix1:x:10000:10000:unix1:/home/unix1:/bin/sh
# getent group unixgrp1
unixgrp1:*:10000:
# id -a unix1
uid=10000(unix1) gid=10000(unixgrp1) groups=10000(unixgrp1)

And moreover, a tcpdump of port 389 will show no unencrypted traffic being used.

9. Verify that Kerberos works

Edit the kerberos krb5.conf file to specify the domain and REALM:

/etc/krb5.conf:

[logging]
 default = FILE:/var/log/krb5libs.log
 kdc = FILE:/var/log/krb5kdc.log
 admin_server = FILE:/var/log/kadmind.log

[libdefaults]
 default_realm = EXAMPLE.COM
 dns_lookup_realm = false
 dns_lookup_kdc = false
 ticket_lifetime = 24h
 renew_lifetime = 7d
 forwardable = true

[realms]
 EXAMPLE.COM = {
  kdc = adserver.example.com
  admin_server = adserver.example.com
 }

[domain_realm]
 .example.com = EXAMPLE.COM
 example.com = EXAMPLE.COM

We can use a user’s ID and password to verify that kerberos works for user principals:

# kinit unix1@EXAMPLE.COM
Password for unix1@EXAMPLE.COM:
# klist -e
Ticket cache: FILE:/tmp/krb5cc_0
Default principal: unix1@EXAMPLE.COM

Valid starting     Expires            Service principal
08/11/11 17:00:17  08/12/11 03:00:25  krbtgt/EXAMPLE.COM@EXAMPLE.COM
        renew until 08/18/11 17:00:17, Etype (skey, tkt): AES-256 CTS mode with 96-bit SHA-1 HMAC, AES-256 CTS mode with 96-bit SHA-1 HMAC

/etc/krb5.conf must be edited to specify the default realm. And “verify_ap_req_nofail = false” can be added to ignore missing host principals (/etc/krb5/krb5.keytab) until they have been set up.

Now for this to be useful, PAM must be configured to use kerberos

10. Configure SSS to use Kerberos

NB. This is really annoying. Whilst commands like “kinit, klist” use /etc/krb5.conf, SSSD on the other hand wants this within /etc/sssd/sssd.conf.

/etc/sssd/sssd.conf:

...
auth_provider = krb5
chpass_provider = krb5
krb5_realm = EXAMPLE.COM
krb5_kdcip = 192.168.102.10
...

11. Configure PAM to use SSS

Linux PAM is divided into multiple files.

Edit /etc/pam.conf to add the pam_krb5.so.1 library file at these locations:

/etc/pam.d/system-auth-ac

#%PAM-1.0
# This file is auto-generated.
# User changes will be destroyed the next time authconfig is run.
auth        required      pam_env.so
auth        sufficient    pam_fprintd.so
auth        sufficient    pam_unix.so nullok try_first_pass
auth        requisite     pam_succeed_if.so uid >= 500 quiet
auth        sufficient    pam_sss.so use_first_pass
auth        required      pam_deny.so

account     required      pam_unix.so
account     sufficient    pam_localuser.so
account     sufficient    pam_succeed_if.so uid < 500 quiet
account     [default=bad success=ok user_unknown=ignore] pam_sss.so
account     required      pam_permit.so

password    requisite     pam_cracklib.so try_first_pass retry=3 type=
password    sufficient    pam_unix.so sha512 shadow nullok try_first_pass use_authtok
password    sufficient    pam_sss.so use_authtok
password    required      pam_deny.so

session     optional      pam_keyinit.so revoke
session     required      pam_limits.so
session     [success=1 default=ignore] pam_succeed_if.so service in crond quiet use_uid
session     required      pam_mkhomedir.so skel=/etc/skel/ umask=0077
session     optional      pam_sss.so
session     required      pam_unix.so 

/etc/pam.d/password-auth-ac

#%PAM-1.0
# This file is auto-generated.
# User changes will be destroyed the next time authconfig is run.
auth        required      pam_env.so
auth        sufficient    pam_unix.so nullok try_first_pass
auth        requisite     pam_succeed_if.so uid >= 500 quiet
auth        sufficient    pam_sss.so use_first_pass
auth        required      pam_deny.so

account     required      pam_unix.so
account     sufficient    pam_localuser.so
account     sufficient    pam_succeed_if.so uid < 500 quiet
account     [default=bad success=ok user_unknown=ignore] pam_sss.so
account     required      pam_permit.so

password    requisite     pam_cracklib.so try_first_pass retry=3 type=
password    sufficient    pam_unix.so sha512 shadow nullok try_first_pass use_authtok
password    sufficient    pam_sss.o use_authtok
password    required      pam_deny.so

session     optional      pam_keyinit.so revoke
session     required      pam_limits.so
session     [success=1 default=ignore] pam_succeed_if.so service in crond quiet use_uid
session     required      pam_unix.so
session     optional      pam_sss.so

12. Verifying Services

Because the pam_mkhomedir.so library is included, the user’s home directory should be created automatically. Then check all the authentication methods (eg console access, ssh, etc)

Login:

Red Hat Enterprise Linux Server release 6.0 (Santiago)
Kernel 2.6.32-71.el6.x86_64 on an x86_64

rhel6host1 login: unix1
Password:
Creating directory '/home/unix1'.
Last login: Thu Aug 11 17:29:08 from localhost.localdomain
-sh-3.2$

SSH:

# ssh unix1@localhost
The authenticity of host 'localhost (::1)' can't be established.
RSA key fingerprint is 15:f2:5b:03:8e:38:fc:d0:ab:4b:06:89:ff:44:54:9b.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added 'localhost' (RSA) to the list of known hosts.
unix1@localhost's password:
Last login: Thu Aug 11 17:31:22 2011 from localhost.localdomain
-sh-4.1$ exit
logout
Connection to localhost closed.

Changing Password:

-sh-4.1$ passwd
Changing password for user unix1.
Current Password:
New password:
Retype new password:
passwd: all authentication tokens updated successfully.

13. Create a host principal keytab in Windows.

To create a host keytab in Windows, first a computer account must exist (this was created in the previous blog). Then create a host principal mapped to that user.

NB. Keytabs need to use the fully qualified domain name.

NB. Keytabs must use encryption which is supported by both ends.

Suggestion: Either use /crypto all, or a known cryptosystem which is supported (eg AES256-SHA1).

There is a Security Policy, which has a checkbox list of all the Supported types:

Security Settings -> Local Policies -> Security Options -> Network Security: Configure encryption types allowed for Kerberos
DES_CBC_CRC
DES_CBC_MD5
RC4_HMAC_MD5
AES128_HMAC_SHA1
AES256_HMAC_SHA1
Future Encryption Types

eg (line split for easy reading)

C:\>ktpass /princ host/rhel6host1.example.com@EXAMPLE.COM \
/ptype KRB5_NT_PRINCIPAL /out C:\temp\rhel6host1.keytab /pass mypass \
/crypto AES256-SHA1 /mapuser EXAMPLE\rhel6host1
Targeting domain controller: adserver.example.com
Successfully mapped host/rhel6host1.example.com to RHEL6HOST1$.
WARNING: Account RHEL6HOST1$ is not a user account (uacflags=0x1021).
WARNING: Resetting RHEL6HOST1$'s password may cause authentication problems if R
HEL6HOST1$ is being used as a server.

Reset RHEL6HOST1$'s password [y/n]?  y
Password succesfully set!
WARNING: pType and account type do not match. This might cause problems.
Key created.
Output keytab to C:\temp\rhel6host1.keytab:
Keytab version: 0x502
keysize 90 host/rhel6host1.example.com@EXAMPLE.COM ptype 1 (KRB5_NT_PRINCIPAL) v
no 3 etype 0x12 (AES256-SHA1) keylength 32 (0x9e2d5c7b1a6d18938d71a652144c33a64e
dd34c47382471a989621f40281dfd2)

This file can now be copied to /etc/krb5.keytab, and verified as follows:

# klist -ke
Keytab name: WRFILE:/etc/krb5.keytab
KVNO Principal
---- --------------------------------------------------------------------------
   3 host/rhel6host1.example.com@EXAMPLE.COM (AES-256 CTS mode with 96-bit SHA-1 HMAC)
# kinit -k 

If kinit doesn’t complain, then principal keytab is working, however, this might not be the end of the story. If an encryption scheme is not allowed, the following message may occur:

Aug 11 11:09:22 localhost sshd[14627]: pam_krb5[14627]: TGT failed verification using keytab and key for ‘host/rhel5host1.example.com@EXAMPLE.COM’: Key table entry not found
Aug 11 11:09:22 localhost sshd[14627]: pam_krb5[14627]: authentication fails for ‘unix1’ (unix1@EXAMPLE.COM): Authentication failure (Success)
Aug 11 11:09:24 localhost sshd[14627]: Failed password for unix1 from 127.0.0.1 port 45476 ssh2

See This Blog for information on keytabs and encryption.

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10 Responses to Authenticating UNIX/Linux to Windows 2008R2. Part 4 : RHEL 6.0

  1. tentastic says:

    Thanks a lot for this! Finally I got it all working. There are too many obsolete guides out there, or only cover one part of the picture, I was going insane trying to get it all up and running.

    Just one question. Apart from not having single sign-on, is there anything wrong with just sticking to ldap for authentication as well?

  2. tentastic says:

    I followed your instructions verbatim except skipped kerberos (step 9,10,13). Instead I put auth_provider ldap and chpass_provider ldap in sssd.conf, and I can login remotely as an AD user. I didn’t configure anything in AD except what you described, it was even a fresh install just for this test.
    Just to be sure I’m not dreaming, I verified the user is not in /etc/passwd, tcpdump shows no kerberos activity, my krb configs are literally untouched defaults, klist/kinit just give errors, and changing the passwd in AD is noticed.
    The only thing that doesn’t work is changing the password, that gives me:
    Password change failed. Server message: 0000203D: LdapErr: DSID-0C090D8C, comment: Unknown extended request OID, data 0, v1db0
    passwd: Authentication token manipulation error

    I’d rather use this for auth than kerberos in some situations (assuming I find no other downsides), so I’ll see if I can get the password change working somehow.

    • Gajanan says:

      Were you able to change the password, can you help me I am getting the same error. How to resolve it?

  3. Mc.Sim says:

    Hi, Chris.
    Can you please tell why you are submitting this section

    [logging]
    default = FILE:/var/log/krb5libs.log
    kdc = FILE:/var/log/krb5kdc.log
    admin_server = FILE:/var/log/kadmind.log

    … in the files / var/log/krb5 *. log do not write?
    And they are empty.

  4. Zapotah says:

    So far this is the best guide on AD integration for linux computers including using ldaps which most guides haven’t covered. However to make secondary groups to work with rfc2307bis schema the ldap_group_member needs to be ldap_group_member = member (which is the default with the specified scheme.). This is covered in sssd documentation, however apparently not emphasized enough.

  5. Pingback: Confluence: Systems

  6. Just Passing says:

    Thanks very much Chris for a guide that really works – 1st time without any pain.

    I discovered the ‘sssd-tools’ package and used its ‘sss_obfuscate’ command to hide the ‘ldap_default_authtok’ from casual browsing. It’s not ‘secure’ because it could still be reverse engineered, but it it a step in the right direction…

    I also made the LDAP bind account a member of the ‘Domain Guests’ group instead of ‘Domain Users’. Group policy could be used to prevent the LDAP bind account from logging-on (locally) to any computer in the domain.

    Do you know if it’s possible/practical to use a client-side certificate instead of storing the LDAP bind account’s password on the client?

    What doesn’t work for me:
    – Password change from a Linux client
    – Automatic creation of home directories

  7. Raule Lodge says:

    Thank you for detail post.

    >>NB. With this, I have been unable to get secondary groups to work.
    I solved problem with secondary group by setting ldap_schema to “rfc2307”, which uses the “memberuid” attribute. It perfectly work in my environment with CentOS 6.3 and Windows Server 2008 R2 SP1.

    ldap_schema = rfc2307

    You can read about this on site:
    https://access.redhat.com/knowledge/docs/en-US/Red_Hat_Enterprise_Linux/6/html/Deployment_Guide/SSSD-Troubleshooting.html

    >> I don’t see any groups with ‘id’ or group members with ‘getent group’.
    >> This may be due to an incorrect ldap_schema setting in the [domain/DOMAINNAME] section of >> sssd.conf.

    >> SSSD supports RFC 2307 and RFC 2307bis schema types. By default, SSSD uses the more >> common RFC 2307 schema.

    >> The difference between RFC 2307 and RFC 2307bis is the way which group membership is stored in the LDAP server. In an RFC 2307 server, group members are stored as the multi-valued memberuid attribute, which contains the name of the users that are members. In an RFC2307bis server, group members are stored as the multi-valued member or uniqueMember attribute which contains the DN of the user or group that is a member of this group. RFC2307bis allows nested groups to be maintained as well.

  8. SeanP says:

    Anyone doing GSSAPI and SSL? I can do either or or but not both I get peer certificate errors.

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