deadmanswitch.sh

#!/usr/bin/env bash

datapath="/usr/local/etc/dms"
dead_man_timestamp_path="${datapath}/dmt"
# Recommended: Any message you put in a message file should have a maximum of 80 characters per line.
dead_man_message_path="${datapath}/dmm"
dead_man_message_warning_path="${datapath}/dmm_warning"
# If you don't want to attach any files, set the variable to ()
# If you intend to share secrets, an encrypted file should be sent as attachment.
# The key should be known to the recipients beforehand.
dead_man_attachment_paths=("${datapath}/message.gpg" "/path/to/other/important/file")
warning_sent="${datapath}/wsent"
dms_sent="${datapath}/dmssent"
dns_killswitch_path="${datapath}/killswitch"
# Don't want to use a DNS killswitch? Set the hostname variable to an empty value.
dns_killswitch_hostname="_quitdms.example.tld"
dns_killswitch_content="\"Sample text\""
# If true, one dns match will disable the killswitch entirely.
# If false or unset, a disappearing record will allow the dead man's switch to activate.
dns_killswitch_permanent=true

[ -f "${dns_killswitch_path}" ] && echo "Permanent killswitch set." && exit 0

if [ -n "${dns_killswitch_hostname}" ]; then
    query_result="$(dig +short -t txt "${dns_killswitch_hostname}")"
    if [ "${dns_killswitch_content}" == "${query_result}" ]; then
        echo "Found killswitch message."
        [ "${dns_killswitch_permanent}" = true ] && touch "${dns_killswitch_path}" && echo "Permanent killswitch set."
        exit 0
    fi
fi

# In this case, the mail(s) have been sent already.
[ -f "${dms_sent}" ] && echo "The switch has been triggered already." && exit 0

dead_name="Your Name"
dead_address="${dead_name} <your@email.address>"
from_address="DMS <no-reply@email.address>"
send_addresses=("One <one@email.address>" "Two <two@email.address>" "Three <three@email.address>")

warningsubject="[DMS] Setting off in 24 hours!"
sentsubject="[DMS] The switch has been set off."
subjectline="${dead_name} is unresponsive, possible death."

[ ! -f "${dead_man_timestamp_path}" ] && echo "Timestamp file not found. Exiting." && exit 1
timestamp="$(cat "${dead_man_timestamp_path}")"
[ -z "${timestamp}" ] && echo "No timestamp in timestamp file. Exiting." && exit 1
time_now="$(date +%s)"

# In hours
time_diff=$(( ( "${time_now}" - "${timestamp}" ) / 3600 ))
echo "${time_diff} hours have passed since the last sign of life."
# 336 hours are 14 days
if [ "$time_diff" -ge 336 ]; then
    echo "The switch is now being triggered."
    mail_text="Last login: $(date --date="@${timestamp}")"$'\n'"$(cat "${dead_man_message_path}")"
    missing_attachments=false
    attachments=()
    for a in "${dead_man_attachment_paths[@]}"; do
        if [ -f "${a}" ]; then
            attachments+=('-a' "${a}")
        elif [ "${missing_attachments}" = false ]; then
            mail_text="${mail_text}"$'\n'$'\n'"Some preplanned attachments could not be attached."
        fi
    done
    for f in "${send_addresses[@]}"; do
        echo "Sending mail to ${f}..."
        printf "%s\n" "${mail_text}" | mail -s "$subjectline" "${attachments[@]}" -r "$from_address" "$f"
    done
    echo "Sending confirmation mail to address of dead person..."
    mail -s "$sentsubject" -r "$from_address" "$dead_address" < /dev/null
    echo "All further executions of this script will now result in an immediate exit."
    touch "${dms_sent}"
    exit 0
fi

# In this case, the mail has been sent already.
[ -f "${warning_sent}" ] && echo "The warning has been sent already." && exit 0

# If the time difference has reached 336-24 hours before the send threshold, we send a warning (if not already done)
if [ "$time_diff" -ge 312 ]; then
    mail_text="Last login: $(date --date="@${timestamp}")"$'\n'"$(cat "${dead_man_message_warning_path}")"
    echo "Sending warning email..."
    printf "%s\n" "${mail_text}" | mail -s "$warningsubject" -r "$from_address" "$dead_address"
    echo "No further warning emails will be sent."
    touch "${warning_sent}"
fi