 ~/ shifterimg --help
Usage:
 shifterimg [options] <mode> <type:tag>

    Mode: images, lookup, or pull

Options:
 --user/-u <list>    List of users allowed to access a private image
 --group/-g <list>   List of groups allowed to access a private image
 --verbose/-v        Verbose output
 --help/-h           Display this help

Note: the --user and --group options are only relevant  for image pulls