iiab/roles/usb_lib/templates/mount.d/70-usb-library.j2

#!/bin/bash
# Create symlink in DocumentRoot/content to automounted usb drive
#
# based on a similar script in the xs-rsync package
# by Martin Langhoff <martin@laptop.org>
#
# and the adaptation for xs-activity-server by Douglas Bagnall
# <douglas@paradise.net.nz>
#
# by Tim Moody tim@timmoody.com

# Better to set this in /etc/usbmount/usbmount.conf
# VERBOSE=yes

# UM_MOUNTPOINT is documented at: https://github.com/rbrito/usbmount#hook-scripts
UM_DEV=$(findmnt -no source $UM_MOUNTPOINT)

# 2022-06-16 better security thanks to @tim-moody and @jvonau:
# https://github.com/iiab/iiab/pull/3254
LIB_DEV=$(findmnt -no source /library | cut -d '[' -f 1)
ROOT_DEV=$(findmnt -no source /)
BOOT_DEV=$(findmnt -no source /boot)
BOOTFW_DEV=$(findmnt -no source /boot/firmware)

# Verbose logging to illuminate occasional boot bugginess:
logger -t "usb_lib (70-usb-library)" "UM_DEV is: $UM_DEV"
logger -t "usb_lib (70-usb-library)" "LIB_DEV is: $LIB_DEV"
logger -t "usb_lib (70-usb-library)" "ROOT_DEV is: $ROOT_DEV"
logger -t "usb_lib (70-usb-library)" "BOOT_DEV is: $BOOT_DEV"
logger -t "usb_lib (70-usb-library)" "BOOTFW_DEV is: $BOOTFW_DEV"

if [ "$UM_DEV" == "$LIB_DEV" ]; then
    logger -t "usb_lib (70-usb-library)" "Skipping $UM_MOUNTPOINT containing /library"
    exit 1
elif [ "$UM_DEV" == "$ROOT_DEV" ]; then
    logger -t "usb_lib (70-usb-library)" "Skipping $UM_MOUNTPOINT containing rootfs"
    exit 1
elif [ "$UM_DEV" == "$BOOT_DEV" ]; then
    logger -t "usb_lib (70-usb-library)" "Skipping $UM_MOUNTPOINT containing /boot"
    exit 1
elif [ "$UM_DEV" == "$BOOTFW_DEV" ]; then
    logger -t "usb_lib (70-usb-library)" "Skipping $UM_MOUNTPOINT containing /boot/firmware"
    exit 1
fi

# 2025-01-25: Check for existence of folder PUBLIC on USB stick: if found, the stick will not be completely browsable.
# Teachers can set their stick for 1 of 2 two "personalities" — students can either upload "confidential homework" or
# "public artwork" — as summarized here: https://github.com/iiab/iiab/blob/master/roles/usb_lib/README.rst
if [ -d $UM_MOUNTPOINT/PUBLIC ]; then
    SHARE_DIR=$UM_MOUNTPOINT/PUBLIC
    logger -t "usb_lib (70-usb-library)" "Found /PUBLIC on $UM_MOUNTPOINT"
else
    SHARE_DIR=$UM_MOUNTPOINT
    logger -t "usb_lib (70-usb-library)" "Did not find /PUBLIC on $UM_MOUNTPOINT"
fi

CONTENT_LINK_USB=$(basename $UM_MOUNTPOINT | awk '{print toupper($0)}')
if [ -z "$CONTENT_LINK_USB" ]; then
    logger -t "usb_lib (70-usb-library)" 'ERROR: Var CONTENT_LINK_USB is empty ("rm -rf /library/www/html/local_content/" would be dangerous!)'
    exit 1
fi
CONTENT_LINK="{{ doc_root }}/local_content/$CONTENT_LINK_USB"
# 'rm -rf' even stronger than 'ln -nsf' and 'ln -Tsf'
# https://serverfault.com/questions/147787/how-to-update-a-symbolic-link-target-ln-f-s-not-working/522483#522483
logger -t "usb_lib (70-usb-library)" "Creating link from $CONTENT_LINK to $SHARE_DIR"
rm -rf $CONTENT_LINK
ln -s $SHARE_DIR $CONTENT_LINK