To use the udisks2 utility commands, type

udisksctl

And you see the options:

$ udisksctl
Usage:
  udisksctl COMMAND

Commands:
  help            Shows this information
  info            Shows information about an object
  dump            Shows information about all objects
  status          Shows high-level status
  monitor         Monitor changes to objects
  mount           Mount a filesystem
  unmount         Unmount a filesystem
  unlock          Unlock an encrypted device
  lock            Lock an encrypted device
  loop-setup      Set-up a loop device
  loop-delete     Delete a loop device
  power-off       Safely power off a drive
  smart-simulate  Set SMART data for a drive

Use "udisksctl COMMAND --help" to get help on each command.

Example

You wanted to unmount a flash drive with udisksctl you will need to get the name of the mounted partition. You can find out with:

lsblk

example output:

NAME         MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sda            8:0    1 15.2G  0 disk 
└─sda1         8:1    1 15.2G  0 part /media/zanna/4C45-110F

so I can unmount this device:

udisksctl unmount -b /dev/sda1

This is reversible with udisksctl mount -b /dev/sda1

In Trusty udisks2 is installed by default and used by nautilus.

The binary is in

/usr/bin/udisksctl

found via dpkg -L udisks2 | grep bin/

from man udisksctl

NAME
       udisksctl - The udisks command line tool

SYNOPSIS
       udisksctl status

       udisksctl info {--object-path OBJECT | --block-device DEVICE}

       udisksctl mount {--object-path OBJECT | --block-device DEVICE} [--filesystem-type TYPE] [--options OPTIONS...] [--no-user-interaction]

       udisksctl unmount {--object-path OBJECT | --block-device DEVICE} [--force] [--no-user-interaction]

       udisksctl unlock {--object-path OBJECT | --block-device DEVICE} [--no-user-interaction]

       udisksctl lock {--object-path OBJECT | --block-device DEVICE} [--no-user-interaction]

       udisksctl loop-setup --file PATH [--read-only] [--offset OFFSET] [--size SIZE] [--no-user-interaction]

       udisksctl loop-delete {--object-path OBJECT | --block-device DEVICE} [--no-user-interaction]

       udisksctl power-off {--object-path OBJECT | --block-device DEVICE} [--no-user-interaction]

       udisksctl smart-simulate --file PATH {--object-path OBJECT | --block-device DEVICE} [--no-user-interaction]

       udisksctl monitor

       udisksctl dump

       udisksctl help

Here is a short test

% sudo apt-get remove udisks2
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following packages will be REMOVED:
  arronax arronax-nautilus brasero deja-dup-backend-gvfs gnome-disk-utility
  gnome-shell-extensions gnome-sushi gvfs gvfs-backends gvfs-backends-goa
  gvfs-daemons gvfs-fuse nautilus nautilus-sendto nautilus-share software-center
  ubuntu-gnome-desktop udisks2 usb-creator-common usb-creator-gtk
0 upgraded, 0 newly installed, 20 to remove and 0 not upgraded.
After this operation, 20,9 MB disk space will be freed.
Do you want to continue? [Y/n]

% sudo apt-get remove udisks
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following packages will be REMOVED:
  udisks
0 upgraded, 0 newly installed, 1 to remove and 0 not upgraded.
After this operation, 1.043 kB disk space will be freed.
Do you want to continue? [Y/n]