/usr/include/net-snmp/system/freebsd7.h is in libsnmp-dev 5.7.2~dfsg-8.1ubuntu3.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 | /* freebsd7 is a superset of freebsd6 */
#include "freebsd6.h"
#define freebsd6 freebsd6
|