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Chapter 7. Troubleshooting

7.1. What Happens when Access is Denied
7.2. Top Three Causes of Problems
7.2.1. Labeling Problems
7.2.2. How are Confined Services Running?
7.2.3. Evolving Rules and Broken Applications
7.3. Fixing Problems
7.3.1. Linux Permissions
7.3.2. Possible Causes of Silent Denials
7.3.3. Manual Pages for Services
7.3.4. Permissive Domains
7.3.5. Searching For and Viewing Denials
7.3.6. Raw Audit Messages
7.3.7. sealert Messages
7.3.8. Allowing Access: audit2allow
The following chapter describes what happens when SELinux denies access; the top three causes of problems; where to find information about correct labeling; analyzing SELinux denials; and creating custom policy modules with audit2allow.

7.1. What Happens when Access is Denied

SELinux decisions, such as allowing or disallowing access, are cached. This cache is known as the Access Vector Cache (AVC). Denial messages are logged when SELinux denies access. These denials are also known as "AVC denials", and are logged to a different location, depending on which daemons are running:
DaemonLog Location
auditd on/var/log/audit/audit.log
auditd off; rsyslogd on/var/log/messages
setroubleshootd, rsyslogd, and auditd on/var/log/audit/audit.log. Easier-to-read denial messages also sent to /var/log/messages
If you are running the X Window System, have the setroubleshoot and setroubleshoot-server packages installed, and the setroubleshootd and auditd daemons are running, a warning is displayed when access is denied by SELinux:
Clicking on 'Show' presents a detailed analysis of why SELinux denied access, and a possible solution for allowing access. If you are not running the X Window System, it is less obvious when access is denied by SELinux. For example, users browsing your website may receive an error similar to the following:

You don't have permission to access file name on this server

For these situations, if DAC rules (standard Linux permissions) allow access, check /var/log/messages and /var/log/audit/audit.log for "SELinux is preventing" and "denied" errors respectively. This can be done by running the following commands as the Linux root user:
grep "SELinux is preventing" /var/log/messages
grep "denied" /var/log/audit/audit.log