postinst is in libsnmp30 5.7.3+dfsg-1ubuntu4.
This file is a maintainer script. It is executed when installing (*inst) or removing (*rm) the package.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 | #! /bin/sh
set -e
ldconfig
exit 0
|