Why isn't rc.local executed?

Question

I am PXE booting some Ubuntu machines in a cluster. All of a sudden my rc.local script has stopped working.

I've check the permission of /etc/rc.local:

-rwxr-xr-x 1 root root 1087 Jan 14 11:04 /etc/rc.local

I've checked that rc.local is symlinked in the following folders:

/etc/rc2.d 
/etc/rc3.d
/etc/rc4.d 
/etc/rc5.d

They all symlink to /etc/init.d/rc.local.

I've tried to output echo lines from the script to /tmp/test.out but no luck. When I execute the rc.local script after the machines has booted, it works fine.

What can cause rc.local not to run?

Solution

I finally got it working. Dunno if this is the best solution, but works for now. I moved the /etc/init.d/rc.local and the /etc/rc.local to a different location, and the I ran

update-rc.d rc.local remove

Afterwards I moved the two scripts back into place and ran

update-rc.d rc.local defaults

It now appears to be working correct.