Troubleshooting Authentication Issues

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Troubleshooting Authentication Issues

In this exercise, you will need to troubleshoot and resolve authentication issues with LDAP, Kerberos, and PAM. *This course is not approved or sponsored by Red Hat.*

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Lab Info

Level

Advanced

Last updated

Oct 26, 2025

Duration

2h 0m

Challenge

Troubleshoot and resolve Server1.
Resolve login issues for testuser01

Try to log in as testuser01:
```
ssh testuser01@localhost
```
View /var/log/secure:
```
tail /var/log/secure
```
Attempt to pull the LDAP user information for testuser01:
```
getent passwd testuser01
```
Perform an LDAP search:
```
ldapsearch -x *
```
View and modify /etc/openldap/ldap.conf:
```
vim /etc/openldap/ldap.conf
```
Change:
```
URI ldap://ldap.example.com/
```
To:
```
URI ldap://auth.example.com/
```
Perform an LDAP search:
```
ldapsearch -x *
```
Restart the LDAP naming services daemon:
```
systemctl restart nslcd
```
Attempt to pull the LDAP user information for testuser01:
```
getent passwd testuser01
```
View /etc/sysconfig/authconfig:
```
cat /etc/sysconfig/authconfig
```
Modify authconfig using the TUI interface:
```
authconfig-tui
```
Within authconfig-tui:
- Verify Use LDAP is checked under User Information
- Check Use Kerberos under Authentication
- Modify the LDAP server to use auth.example.com
- Use auth.example.com for the KDC and Admin Server for Kerberos
Restart the LDAP naming services daemon:
```
systemctl restart nslcd
```
Pull the LDAP user information for testuser01:
```
getent passwd testuser01
```
Log in to the localhost as testuser01:
```
ssh testuser01@localhost
```
Obtain a Kerberos ticket
```
kinit
```
List cached Kerberos tickets and logout:
```
klist && exit
```
Resolve Samba issues for cloud_user

Verify Samba is started and enabled:
```
systemctl start smb && systemctl enable smb
```
Attempt to list the shares using cloud_user:
```
smbclient -U cloud_user -L localhost
```
View the Samba log:
```
tail /var/log/samba/log.smbd
```
View the Samba PAM config:
```
cat /etc/pam.d/samba
```
Verify the Samba package:
```
rpm -V samba
```
Move the modified file to /root/samba.pam.old:
```
mv /etc/pam.d/samba /root/samba.pam.old
```
Reinstall Samba:
```
yum reinstall -y samba
```
List the shares using cloud_user:
```
smbclient -U cloud_user -L localhost
```
Challenge

Troubleshoot and resolve Server2.
Use authconfig-tui to verify and modify LDAP/Kerberos authentication:
```
authconfig-tui
```
- Verify Use LDAP is checked for both User Information and Authentication
- Verify Use Kerberos is checked for Authentication
- LDAP server should be auth.example.com
- Kerberos KDC and Admin should be auth.example.com
Perform an LDAP search:
```
ldapsearch -x *
```
Ping the LDAP server:
```
ping auth.example.com
```
Note the IP, view the contents of /etc/hosts:
```
cat /etc/hosts
```
Modify /etc/hosts so that auth.example.com points to 10.0.1.5:
```
vim /etc/hosts
```
Perform an LDAP search:
```
ldapsearch -x *
```
Restart the LDAP naming services daemon:
```
systemctl restart nslcd
```
Pull the LDAP user information for testuser01:
```
getent passwd testuser01
```
Log in as testuser01:
```
ssh testuser01@localhost
```
Obtain a Kerberos ticket:
```
kinit
```
List Kerberos ticket cache:
```
klist
```

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