/var/lib/cobbler/snippets/disable_pxe is in cobbler-common 2.4.1-0ubuntu2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 | #if $pxe_just_once in [ "1", "true", "yes", "y" ]
wget "http://$http_server:$http_port/cblr/svc/op/nopxe/system/$system_name" -O /dev/null \
#end if
|