This file is indexed.

/etc/network/if-up.d/openssh-server is in openssh-server 1:7.6p1-4ubuntu0.3.

This file is owned by root:root, with mode 0o755.

The actual contents of the file can be viewed below.

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#! /bin/sh
# Reload the OpenSSH server when an interface comes up, to allow it to start
# listening on new addresses.

set -e

# Don't bother to restart sshd when lo is configured.
if [ "$IFACE" = lo ]; then
	exit 0
fi

# Only run from ifup.
if [ "$MODE" != start ]; then
	exit 0
fi

# OpenSSH only cares about inet and inet6. Get ye gone, strange people
# still using ipx.
if [ "$ADDRFAM" != inet ] && [ "$ADDRFAM" != inet6 ]; then
	exit 0
fi

# Is /usr mounted?
if [ ! -e /usr/sbin/sshd ]; then
	exit 0
fi

if [ ! -f /run/sshd.pid ] || \
   [ "$(ps -p "$(cat /run/sshd.pid)" -o comm=)" != sshd ]; then
	exit 0
fi

# We'd like to use 'reload' here, but it has some problems; see #502444.  On
# the other hand, repeated restarts of ssh make systemd unhappy
# (#756547/#757822), so use reload in that case.
if [ -d /run/systemd/system ]; then
	systemctl reload --no-block ssh.service >/dev/null 2>&1 || true
else
	invoke-rc.d ssh restart >/dev/null 2>&1 || true
fi

exit 0