Dockerfiles and scripts to build various Docker images I rely on.
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#!/usr/bin/env bash
if [[ -z "${TARGET_UID}" ]]; then
echo "Error: The TARGET_UID environment variable was not specified.";
exit 1;
if [[ -z "${TARGET_GID}" ]]; then
echo "Error: The TARGET_GID environment variable was not specified.";
exit 1;
if [[ "${EUID}" -ne 0 ]]; then
echo "Error: This Docker container must run as root because fetchmail is a pain, and to allow customisation of the target UID/GID (although all possible actions are run as non-root users)";
exit 1;
fetchmail_uid="$(id -u "fetchmail")";
fetchmail_gid="$(id -g "fetchmail")";
temp_dir="$(mktemp --tmpdir -d "imap-download-XXXXXXX")";
on_exit() {
rm -rf "${temp_dir}";
trap on_exit EXIT;
run_as_user() {
run_as_uid="${1}"; shift;
run_as_gid="${1}"; shift;
if [[ -z "${run_as_uid}" ]]; then
echo "run_as_user: No target UID specified.";
return 1;
if [[ -z "${run_as_gid}" ]]; then
echo "run_as_user: No target GID specified.";
return 2;
# Ref
# WORKAROUND for `setpriv: libcap-ng is too old for "all" caps`, previously "-all" was used here
# create a list to drop all capabilities supported by current kernel
caps="$cap_prefix$(seq -s ",$cap_prefix" 0 "$(cat /proc/sys/kernel/cap_last_cap)")";
setpriv --inh-caps="${caps}" --reuid "${run_as_uid}" --clear-groups --regid "${run_as_gid}" "$@";
return "$?";
do_fetchmail() {
log_msg "Starting fetchmail";
while :; do
run_as_user "${fetchmail_uid}" "${fetchmail_gid}" fetchmail --mda "/usr/bin/procmail -m /srv/procmail.conf";
if [[ "$exit_code" -eq 127 ]]; then
log_msg "setpriv failed, exiting with code 127";
exit 127;
log_msg "Fetchmail exited with code ${exit_code}, sleeping 60 seconds";
sleep 60
log_msg() {
echo "$(date -u +"%Y-%m-%d %H:%M:%S") imap-download: $*";
mkdir -p "${dir_newmail}";
chown -R "${fetchmail_uid}:${fetchmail_gid}" "${dir_mail_root}";
do_attachments() {
while :; do # : = infinite loop
# Wait for an update
# inotifywait's non-0 exit code forces an exit for some reason :-/
inotifywait -qr --event create --format '%:e %f' "${dir_newmail}";
while read -r filename; do
log_msg "Processing email ${filename}";
# Move the email to a temporary directory for processing
mv "${filename}" "${temp_dir}";
filepath_temp="${temp_dir}/$(basename "${filename}")"
# Unpack the attachments
munpack -C "${temp_dir}" "${filepath_temp}";
# Delete the original email file and any description files
rm "${filepath_temp}";
find "${temp_dir}" -iname '*.desc' -delete;
chown -R "${TARGET_UID}:${TARGET_GID}" "${temp_dir}";
chmod -R a=rX,ug+w "${temp_dir}";
ls -lahR "${temp_dir}";
# Move the attachment files to the output directory
while read -r attachment; do
log_msg "Extracted attachment ${attachment}";
chmod 0775 "${attachment}";
run_as_user "${TARGET_UID}" "${TARGET_GID}" mv "${attachment}" "${target_dir}";
done < <(find "${temp_dir}" -type f);
done < <(find "${dir_newmail}" -type f);
do_fetchmail &