After several false starts I figured this out. The key is to add a systemd unit service between udev and a mounting script.
(For the record, I was not able to get this working using udisks2 (via something like udisksctl mount -b /dev/sdb1) called either directly from a udev rule or from a systemd unit file. There seems to be a race condition and the device node isn't quite ready, resulting in Error looking up object for device /dev/sdb1. Unfortunate, since udisks2 could take care of all the mount point messyness...)
The heavy lifting is done by a shell script, which takes care of creating and removing mount points, and mounting and unmounting the drives.
/usr/local/bin/usb-mount.sh
#!/bin/bash # This script is called from our systemd unit file to mount or unmount # a USB drive. usage() { echo "Usage: $0 {add|remove} device_name (e.g. sdb1)" exit 1 } if [[ $# -ne 2 ]]; then usage fi ACTION=$1 DEVBASE=$2 DEVICE="/dev/${DEVBASE}" # See if this drive is already mounted, and if so where MOUNT_POINT=$(/bin/mount | /bin/grep ${DEVICE} | /usr/bin/awk '{ print $3 }') do_mount() { if [[ -n ${MOUNT_POINT} ]]; then echo "Warning: ${DEVICE} is already mounted at ${MOUNT_POINT}" exit 1 fi # Get info for this drive: $ID_FS_LABEL, $ID_FS_UUID, and $ID_FS_TYPE eval $(/sbin/blkid -o udev ${DEVICE}) # Figure out a mount point to use LABEL=${ID_FS_LABEL} if [[ -z "${LABEL}" ]]; then LABEL=${DEVBASE} elif /bin/grep -q " /media/${LABEL} " /etc/mtab; then # Already in use, make a unique one LABEL+="-${DEVBASE}" fi MOUNT_POINT="/media/${LABEL}" echo "Mount point: ${MOUNT_POINT}" /bin/mkdir -p ${MOUNT_POINT} # Global mount options OPTS="rw,relatime" # File system type specific mount options if [[ ${ID_FS_TYPE} == "vfat" ]]; then OPTS+=",users,gid=100,umask=000,shortname=mixed,utf8=1,flush" fi if ! /bin/mount -o ${OPTS} ${DEVICE} ${MOUNT_POINT}; then echo "Error mounting ${DEVICE} (status = $?)" /bin/rmdir ${MOUNT_POINT} exit 1 fi echo "**** Mounted ${DEVICE} at ${MOUNT_POINT} ****" } do_unmount() { if [[ -z ${MOUNT_POINT} ]]; then echo "Warning: ${DEVICE} is not mounted" else /bin/umount -l ${DEVICE} echo "**** Unmounted ${DEVICE}" fi # Delete all empty dirs in /media that aren't being used as mount # points. This is kind of overkill, but if the drive was unmounted # prior to removal we no longer know its mount point, and we don't # want to leave it orphaned... for f in /media/* ; do if [[ -n $(/usr/bin/find "$f" -maxdepth 0 -type d -empty) ]]; then if ! /bin/grep -q " $f " /etc/mtab; then echo "**** Removing mount point $f" /bin/rmdir "$f" fi fi done } case "${ACTION}" in add) do_mount ;; remove) do_unmount ;; *) usage ;; esac
The script, in turn, is called by a systemd unit file. We use the "@" filename syntax so we can pass the device name as an argument.
/etc/systemd/system/[email protected]
[Unit] Description=Mount USB Drive on %i [Service] Type=oneshot RemainAfterExit=true ExecStart=/usr/local/bin/usb-mount.sh add %i ExecStop=/usr/local/bin/usb-mount.sh remove %i
Finally, some udev rules start and stop the systemd unit service on hotplug/unplug:
/etc/udev/rules.d/99-local.rules
KERNEL=="sd[a-z][0-9]", SUBSYSTEMS=="usb", ACTION=="add", RUN+="/bin/systemctl start usb-mount@%k.service" KERNEL=="sd[a-z][0-9]", SUBSYSTEMS=="usb", ACTION=="remove", RUN+="/bin/systemctl stop usb-mount@%k.service"
This seems to do the trick! A couple of useful commands for debugging stuff like this:
udevadm control -l debug turns on verbose logging to /var/log/syslog so you can see what's happening.udevadm control --reload-rules after you modify files in the rules.d dir (may not be necessary, but can't hurt...).systemctl daemon-reload after you modify systemd unit files.
