unused-for is a deprecated synonym
See
@@ -45,7 +45,7 @@ func NewPruneCommand(dockerCli command.Cli) *cobra.Command {
flags := cmd.Flags()
flags.BoolVarP(&options.force, "force", "f", false, "Do not prompt for confirmation")
flags.BoolVarP(&options.all, "all", "a", false, "Remove all unused images, not just dangling ones")
- flags.Var(&options.filter, "filter", "Provide filter values (e.g. 'unused-for=24h')")
+ flags.Var(&options.filter, "filter", "Provide filter values (e.g. 'until=24h')")
flags.Var(&options.keepStorage, "keep-storage", "Amount of disk space to keep for cache")
return cmd
