I ran into some problems with MySQL on RHEL 4 when SELinux was enabled. When starting MySQL it would come up with this:

Starting MySQL...................................[FAILED]

And the following in /var/log/messages:

[code]Dec 1 14:02:52 searchdev kernel: audit(1164934972.432:5): avc: denied { append } for pid=3071 comm=”mysqld” name=”searchdev.err” dev=sda6 ino=1687755 scontext=root:system_r:mysqld_t tcontext=root:object_r:var_lib_t tclass=file[/code]

All fixed though thanks to this page: http://bugs.mysql.com/bug.php?id=12676