Bash script to automatically reboot if the network connection goes down

ensure-network.service

[Unit]
Description=Reboot if the network connection is down
After=network.target

[Service]
Type=simple
# Because it needs to be able to reboot
User=root
Group=root
EnvironmentFile=-/etc/default/ensure-network
ExecStartPre=/bin/sleep 60
ExecStart=/bin/bash "/usr/local/lib/ensure-network/ensure-network.sh"
SyslogIdentifier=ensure-access
StandardError=syslog
StandardOutput=syslog

[Install]
WantedBy=multi-user.target

ensure-network.sh

#!/usr/bin/env bash

# ███████ ███    ██ ███████ ██    ██ ██████  ███████
# ██      ████   ██ ██      ██    ██ ██   ██ ██
# █████   ██ ██  ██ ███████ ██    ██ ██████  █████ █████
# ██      ██  ██ ██      ██ ██    ██ ██   ██ ██
# ███████ ██   ████ ███████  ██████  ██   ██ ███████
# 
# ███    ██ ███████ ████████ ██     ██  ██████  ██████  ██   ██
# ████   ██ ██         ██    ██     ██ ██    ██ ██   ██ ██  ██
# ██ ██  ██ █████      ██    ██  █  ██ ██    ██ ██████  █████
# ██  ██ ██ ██         ██    ██ ███ ██ ██    ██ ██   ██ ██  ██
# ██   ████ ███████    ██     ███ ███   ██████  ██   ██ ██   ██
# 
# By Starbeamrainbowlabs
# 
# Changelog:
### 15th June 2020
##### Initial Release
# 
# This script is licenced under the Mozilla Public Licence 2.0.
# See the full legal text here: https://www.mozilla.org/MPL/2.0/
# See a summary of the licence here: https://tldrlegal.com/license/mozilla-public-license-2.0-(mpl-2)
# 
# Contributions are welcome!
# Please also consider getting in touch if you're using this script, as it'd be great to hear how people are using it.
# 
# Associated blog post: 
# (leave a comment on here if you like!)
# 


CHECK_EXTERNAL_HOST="${CHECK_EXTERNAL_HOST:-starbeamrainbowlabs.com}";	# External host to check against
CHECK_INTERVAL="${CHECK_INTERVAL:-3600}";		# In seconds
CHECK_TIMEOUT="${CHECK_TIMEOUT:-5}"				# In seconds
CHECK_RETRIES="${CHECK_RETRIES:-5}";			# Retry this many times before rebooting
CHECK_RETRY_DELAY="${CHECK_RETRY_DELAY:-60}";	# Delay this many seconds between retries
CHECK_DRY_RUN="${CHECK_DRY_RUN:-false}";		# Whether to to a dry run or not
CHECK_REBOOT_DELAY="60";						# In *minutes* - reboot at most every hour
# If this file exists and has an mtime in the past 7 days, delay restarting
CHECK_POSTPONE_FILE="${CHECK_POSTPONE_FILE}";
CHECK_POSTPONE_MAXAGE="10080"					# In *minutes* - default: 7 days

# Use this file to properly delay reboots
__reboot_delay_file="${__reboot_delay_file:-/var/cache/ensure-network}";

###############################################################################

log_msg() {
	echo -ne "[$(date -u +"%Y-%m-%d %H:%M:%S")] $*";
	if [[ -z "${NO_NEWLINE}" ]]; then
		echo;
	fi
}

# From https://github.com/dylanaraps/pure-bash-bible#use-read-as-an-alternative-to-the-sleep-command
# Usage: snore 1
#        snore 0.2
snore() {
	log_msg "[snore] Sleeping for ${1}s"
	read -rt "$1" <> <(:) || :
}

# From https://stackoverflow.com/a/59643790/1460422
file_age() {
	local filename="${1}"
	if [[ -z "${filename}" ]]; then
		echo "[file_age] Error: filenam may not my empty";
		return 1;
	fi
	echo "$(( $(date +%s) - $(date -r $filename +%s) ))"
}

# $1	The filename to check
# $2	The maximum number of minutes the file's age is allowed to be before it is marked stale
is_stale() {
	local filename="${1}";
	local max_minutes="${2:-20}";
	[ $(file_age $filename) -gt $(( $max_minutes*60 )) ]
}

is_fresh() {
	is_stale "${1}" "${2}";
	if [[ "$?" -eq 0 ]]; then return 1; else return 0; fi
}

###############################################################################

while :; do
	log_msg "Checking for connection";
	got_connection="false";
	for (( i = 0; i < "${CHECK_RETRIES}"; i++ )); do
		NO_NEWLINE=true log_msg "Check attempt $i: ";
		transcript="$(ping -c1 "${CHECK_EXTERNAL_HOST}" -W "${CHECK_TIMEOUT}" 2>&1)";
		exit_code="$?";
		if [[ "${exit_code}" -eq "0" ]]; then
			echo "success";
			got_connection="true";
			break;
		fi
		echo "failed with code ${exit_code}";
		log_msg "${transcript}";
		
		snore "${CHECK_RETRY_DELAY}";
	done
	
	if [[ "${got_connection}" != "true" ]]; then
		log_msg "Failed to get a connection after ${CHECK_RETRIES} attempts.";
		if [[ ! -z "${CHECK_POSTPONE_FILE}" ]] && is_fresh "${CHECK_POSTPONE_FILE}" "${CHECK_POSTPONE_MAXAGE}"; then
			log_msg "Fresh postpone file detected, delaying reboot";
			snore "${CHECK_INTERVAL}";
			continue;
		else
			log_msg "No fresh postpone file detected";
		fi
		
		if [[ -f "${__reboot_delay_file}" ]] && is_fresh "${__reboot_delay_file}" "${CHECK_REBOOT_DELAY}"; then
			log_msg "It's been less than ${CHECK_REBOOT_DELAY}s since the last reboot, delaying";
			continue;
		else
			log_msg "Last reboot was more than ${CHECK_REBOOT_DELAY}s ago";
		fi
		
		touch "${__reboot_delay_file}";
		
		log_msg "Rebooting.";
		if [[ "${CHECK_DRY_RUN}" == "false" ]]; then
			reboot;
		else
			while :; do snore 9999999; done
		fi
	else
		log_msg "Got connection after ${i} attempts";
	fi
	
	snore "${CHECK_INTERVAL}";
done