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I have a system with multiple USBs connected. I would like to find a USB that contains a specific .ini file or is empty (in which case I want to create the .ini file) and mount it at /media/mount_point. If no such USB exists then nothing should be mounted.

I have tried creating a udev rule which runs the following script for each USB:

#!/bin/sh LOGFILE="/home/user/mount.log" MOUNTDIRECTORY="/media/mount_point" if [ -z "$DEVNAME" ]; then exit fi echo "USB device detected at $DEVNAME" >> $LOGFILE if grep '$MOUNTDIRECTORY ' /proc/mounts; then # Already mounted echo "Mount directory already in use" >> $LOGFILE exit fi mount $DEVNAME $MOUNTDIRECTORY -o umask=0000,gid=1000,uid=1000 &>> $LOGFILE if [ $? -eq 0 ]; then echo "$DEVNAME mounted at $MOUNTDIRECTORY" >> $LOGFILE if [ -f $MOUNTDIRECTORY/log.ini ]; then echo "Log.ini found. Ready to log" >> $LOGFILE break elif [ -z "$(ls -A $MOUNTDIRECTORY)" ]; then echo "USB device empty. Creating log.ini" >> $LOGFILE touch $MOUNTDIRECTORY/log.ini break else umount $MOUNTDIRECTORY fi else echo "Failed to mount $DEVNAME at $MOUNTDIRECTORY" >> $LOGFILE fi echo "" >> $LOGFILE

This works if the .ini exists (after editing systemd-udevd.service per this question), but not if an empty USB is found. The $LOGFILE output reports that an .ini has been created, but if I check then there is no .ini file on the mounted device. If I unmount, I find the .ini file has been created at the mount point instead.

Why does the .ini file end up at the mount point rather than on the mounted USB? How can I fix this?

Alternatively, is there a better approach than udev for this problem?

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I have been able to find a satisfactory solution.

Rather than attempt to mount from udev directly, I instead spawned a new service as suggested in this question. Ultimately I ended up with this udev rule:

ACTION=="add",<Your device specifiers here>,ENV{SYSTEMD_WANTS}="log@$env{DEVPATH}.service"

Added the following service to /etc/systemd/system:

[Service] Type=oneshot TimeoutStartSec=300 GuessMainPID=false RemainAfterExit=yes ExecStart=/bin/bash -c "/home/user/mount.sh %I"

And modified my script to:

#!/bin/sh LOGFILE="/home/user/mount.log" MOUNTDIRECTORY="/media/mount_point" DEVPATH=$1 BASENAME="$(basename $DEVPATH)" DEVICE="/dev/$BASENAME" if [ -z "$BASENAME" ]; then exit fi echo "" >> $LOGFILE echo "New USB device detected at $DEVICE" >> $LOGFILE if grep '$MOUNTDIRECTORY ' /proc/mounts; then # Already mounted echo "Mount directory already in use" >> $LOGFILE exit fi mount $DEVICE $MOUNTDIRECTORY -o umask=0000,gid=1000,uid=1000 >> $LOGFILE if [ $? -eq 0 ]; then echo "$DEVICE mounted at $MOUNTDIRECTORY" >> $LOGFILE if [ -f $MOUNTDIRECTORY/log.ini ]; then echo "Log.ini found. Ready to log" >> $LOGFILE break elif [ -z "$(ls -A $MOUNTDIRECTORY)" ]; then echo "USB device empty. Creating log.ini" >> $LOGFILE touch $MOUNTDIRECTORY/log.ini break else echo "Log.ini not found. Unmounting" >> $LOGFILE umount $MOUNTDIRECTORY fi else echo "Failed to mount $DEVICE at $MOUNTDIRECTORY" >> $LOGFILE fi echo "" >> $LOGFILE

I still don't understand the cause of my original issue (log.ini file appearing at the mount point rather than one the mounted device). If anyone has an explanation I would be interested.

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