Now Iwhen I try to login to the web interface, the browser reports "Internal server error"; setroubleshoot shows I'm getting SELinux errors on the sessions:
[snip]

*****  Plugin restorecon (99.5 confidence) suggests  *************************

If you want to fix the label.
/var/lib/cobbler/webui_sessions/sessionidc784de1d76c5e28c949a78aaafb414de default label should be httpd_sys_rw_content_t.
Then you can run restorecon.
Do
# /sbin/restorecon -v /var/lib/cobbler/webui_sessions/sessionidc784de1d76c5e28c949a78aaafb414de
[snip]
# ll -Zd /var/lib/cobbler/webui_sessions/
drwxrwxr-x. apache apache system_u:object_r:cobbler_var_lib_t:s0 /var/lib/cobbler/webui_sessions//

-- 
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
Robert Jacobson               Robert.C.Jacobson@nasa.gov
Lead System Admin       Solar Dynamics Observatory (SDO)
Bldg 14, E222                             (301) 286-1591