postinst is in socklog 2.1.0-8.
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 | #!/bin/sh
set -e
test "$1" = 'configure' || exit 0
getent passwd log >/dev/null || \
adduser --system --home /nonexistent --no-create-home log
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