Udev-based MTP Automounter (uma)

Mounts newly attached MTP devices using go-mtpfs with options for user defined mountpoints.

Designed as a simple and lightweight alternative to desktop based solutions (gvfs/kio) for automounting MTP devices.

Installation

Dependencies

• A Linux system with systemd and udev, any mainstream linux distribution should work.

• go-mtpfs

• libmtp

On Ubuntu go-mtpfs and libmtp can be installed with the command:

sudo apt install go-mtpfs libmtp-common

Install uma

git clone https://github.com/jmoggr/uma.git
cd uma
make
sudo make install

Use

Mounting

1. Plug the MTP enabled USB device in

2. Enable USB file transfer on device

3. Device should appear mounted in /media

Unmounting

1. Unplug the device

MTP expects that the device can be removed at any time and offers no safely remove feature. It is up to the user to ensure that any file transfers to/from the device have completed before removing it, otherwise corrupted partially completed transfers may occur.

Event Hooks

By default event hooks are stored in /opt/uma/hooks, which contains a subdirectory for each event type: - pre-mount - post-mount - post-umount

To install a hook for an event, place an executable file which will run the hook in the appropriate event type folder.

Notes:

• When an event is triggered each executable in the relevant event type subdirectory is run.

• Mounting will be blocked until the pre-mount hooks have exited.

• By default there is a 30s time limit on the aggregate runtime of all hooks for each event. This is configured by the TimeoutStartSec for pre-mount and post-mount hooks and TimeoutStopSec for the post-umount hooks

• If a hook exits with failure, no subsequent hooks will be run. Hook failure does not impact the main mounting/unmounting process.

• Hook executables are `source`ed, so all hooks for an event share the same environment.

• Systemd provides no ExecStopPre parameter, so there is no pre-umount event. However a pre-umount event wouldn’t make sense anyway because the device is simply removed.

configuration

See uma.conf

Troubleshooting

Control Flow

On USB device addition

udev

• Check if the device is marked as having MTP support — /lib/udev/rules.d/69-libmtp.rules

• if it is, start a uma-mount service instance for the device — 80-uma.rules

  systemd — [email protected]

  • Run pre-start script

    script — uma-hookrunner pre-mount

    • run pre-mount hooks — hooks/post-mount/*

  • run main mount manager script

    script — uma-mount

    • find a suitable mountpoint

    • record the device and mountpoint — MOUNTS_FILE

    • start go-mtpfs

    • when go-mtpfs has mounted the MTP device, signal that the service startup is complete

  • Run post-start script

    script — uma-hookrunner post-mount

    • run post-mount hooks — hooks/post-mount/*

On USB device removal

udev

• if the device is MTP — 70-mtp-remove.rules

• if it is, stop the mount service — 80-uma.rules

  systemd

  • run stop script — [email protected]

    script — uma-mount

    • get device mountpoint — MOUNTS_FILE

    • unmount, this causes the go-mtpfs process to exit normally, which causes the service process to exit normally

    • delete mountpoint

    • delete record of device and mountpoint

  • Run post-stop script

    script — uma-hookrunner post-umount

    • run post-umount hooks — hooks/post-umount/*

On system restart

systemd

• run cleanup script — uma-cleanup.service

  script — uma-cleanup

  • Removes remaining entries in MOUNTS_FILE and the corresponding mountpoints.

Debugging