func (c *restoreCommand) Init(args []string) error {
	if err := c.EnvCommandBase.EnsureEnvName(); err != nil {
		return err
	}
	if c.showDescription {
		return cmd.CheckEmpty(args)
	}
	if len(args) == 0 {
		return fmt.Errorf("no backup file specified")
	}
	c.backupFile = args[0]
	return cmd.CheckEmpty(args[1:])
}

func (c *BootstrapCommand) Init(args []string) (err error) {
	if err := c.EnvCommandBase.EnsureEnvName(); err != nil {
		return err
	}
	if len(c.Series) > 0 && !c.UploadTools {
		return fmt.Errorf("--upload-series requires --upload-tools")
	}
	if len(c.seriesOld) > 0 && !c.UploadTools {
		return fmt.Errorf("--series requires --upload-tools")
	}
	if len(c.Series) > 0 && len(c.seriesOld) > 0 {
		return fmt.Errorf("--upload-series and --series can't be used together")
	}
	if len(c.seriesOld) > 0 {
		c.Series = c.seriesOld
	}

	// Parse the placement directive. Bootstrap currently only
	// supports provider-specific placement directives.
	if c.Placement != "" {
		_, err = instance.ParsePlacement(c.Placement)
		if err != instance.ErrPlacementScopeMissing {
			// We only support unscoped placement directives for bootstrap.
			return fmt.Errorf("unsupported bootstrap placement directive %q", c.Placement)
		}
	}
	return cmd.CheckEmpty(args)
}

func (c *UpgradeJujuCommand) Init(args []string) error {
	if err := c.EnvCommandBase.EnsureEnvName(); err != nil {
		return err
	}
	if c.vers != "" {
		vers, err := version.Parse(c.vers)
		if err != nil {
			return err
		}
		if vers.Major != version.Current.Major {
			return fmt.Errorf("cannot upgrade to version incompatible with CLI")
		}
		if c.UploadTools && vers.Build != 0 {
			// TODO(fwereade): when we start taking versions from actual built
			// code, we should disable --version when used with --upload-tools.
			// For now, it's the only way to experiment with version upgrade
			// behaviour live, so the only restriction is that Build cannot
			// be used (because its value needs to be chosen internally so as
			// not to collide with existing tools).
			return fmt.Errorf("cannot specify build number when uploading tools")
		}
		c.Version = vers
	}
	if len(c.Series) > 0 && !c.UploadTools {
		return fmt.Errorf("--series requires --upload-tools")
	}
	return cmd.CheckEmpty(args)
}

func (c *portCommand) Init(args []string) error {
	if args == nil {
		return errors.New("no port specified")
	}
	parts := strings.Split(args[0], "/")
	if len(parts) > 2 {
		return fmt.Errorf("expected %s; got %q", portFormat, args[0])
	}
	port, err := strconv.Atoi(parts[0])
	if err != nil {
		return badPort(parts[0])
	}
	if port < 1 || port > 65535 {
		return badPort(port)
	}
	protocol := "tcp"
	if len(parts) == 2 {
		protocol = strings.ToLower(parts[1])
		if protocol != "tcp" && protocol != "udp" {
			return fmt.Errorf(`protocol must be "tcp" or "udp"; got %q`, protocol)
		}
	}
	c.Port = port
	c.Protocol = protocol
	return cmd.CheckEmpty(args[1:])
}

func (c *SignMetadataCommand) Init(args []string) error {
	if c.dir == "" {
		return fmt.Errorf("directory must be specified")
	}
	if c.keyFile == "" {
		return fmt.Errorf("keyfile must be specified")
	}
	return cmd.CheckEmpty(args)
}

func (c *EnsureAvailabilityCommand) Init(args []string) error {
	if err := c.EnsureEnvName(); err != nil {
		return err
	}
	if c.NumStateServers < 0 || (c.NumStateServers%2 != 1 && c.NumStateServers != 0) {
		return fmt.Errorf("must specify a number of state servers odd and non-negative")
	}
	return cmd.CheckEmpty(args)
}

func (c *UnitGetCommand) Init(args []string) error {
	if args == nil {
		return errors.New("no setting specified")
	}
	if args[0] != "private-address" && args[0] != "public-address" {
		return fmt.Errorf("unknown setting %q", args[0])
	}
	c.Key = args[0]
	return cmd.CheckEmpty(args[1:])
}

func (c *OwnerGetCommand) Init(args []string) error {
	if args == nil {
		return errors.New("no setting specified")
	}
	if args[0] != "tag" {
		return fmt.Errorf("unknown setting %q", args[0])
	}
	c.Key = args[0]
	return cmd.CheckEmpty(args[1:])
}

func (c *UnexposeCommand) Init(args []string) error {
	if err := c.EnsureEnvName(); err != nil {
		return err
	}
	if len(args) == 0 {
		return errors.New("no service name specified")
	}
	c.ServiceName = args[0]
	return cmd.CheckEmpty(args[1:])
}

func (c *PublishCommand) Init(args []string) error {
	if err := c.EnvCommandBase.EnsureEnvName(); err != nil {
		return err
	}
	if len(args) == 0 {
		return nil
	}
	c.URL = args[0]
	return cmd.CheckEmpty(args[1:])
}

func (c *RemoveUserCommand) Init(args []string) error {
	if err := c.EnsureEnvName(); err != nil {
		return err
	}
	if len(args) == 0 {
		return errors.New("no username supplied")
	}
	c.User = args[0]

	return cmd.CheckEmpty(args[1:])
}

func (c *GetCommand) Init(args []string) error {
	if err := c.EnvCommandBase.EnsureEnvName(); err != nil {
		return err
	}
	// TODO(dfc) add --schema-only
	if len(args) == 0 {
		return errors.New("no service name specified")
	}
	c.ServiceName = args[0]
	return cmd.CheckEmpty(args[1:])
}

func (c *ConfigGetCommand) Init(args []string) error {
	if args == nil {
		return nil
	}
	c.Key = args[0]
	if c.Key != "" && c.All {
		return fmt.Errorf("cannot use argument --all together with key %q", c.Key)
	}

	return cmd.CheckEmpty(args[1:])
}

func (c *GetConstraintsCommand) Init(args []string) error {
	if err := c.EnvCommandBase.EnsureEnvName(); err != nil {
		return err
	}
	if len(args) > 0 {
		if !names.IsService(args[0]) {
			return fmt.Errorf("invalid service name %q", args[0])
		}
		c.ServiceName, args = args[0], args[1:]
	}
	return cmd.CheckEmpty(args)
}

func (c *RelationIdsCommand) Init(args []string) error {
	if r, found := c.ctx.HookRelation(); found {
		c.Name = r.Name()
	}
	if len(args) > 0 {
		c.Name = args[0]
		args = args[1:]
	} else if c.Name == "" {
		return fmt.Errorf("no relation name specified")
	}
	return cmd.CheckEmpty(args)
}

func (c *DestroyServiceCommand) Init(args []string) error {
	if err := c.EnsureEnvName(); err != nil {
		return err
	}
	if len(args) == 0 {
		return fmt.Errorf("no service specified")
	}
	if !names.IsService(args[0]) {
		return fmt.Errorf("invalid service name %q", args[0])
	}
	c.ServiceName, args = args[0], args[1:]
	return cmd.CheckEmpty(args)
}

func (c *DebugLogCommand) Init(args []string) error {
	if err := c.EnsureEnvName(); err != nil {
		return err
	}
	if c.level != "" {
		level, ok := loggo.ParseLevel(c.level)
		if !ok || level < loggo.TRACE || level > loggo.ERROR {
			return fmt.Errorf("level value %q is not one of %q, %q, %q, %q, %q",
				c.level, loggo.TRACE, loggo.DEBUG, loggo.INFO, loggo.WARNING, loggo.ERROR)
		}
		c.params.Level = level
	}
	return cmd.CheckEmpty(args)
}

func (c *AddUnitCommand) Init(args []string) error {
	if err := c.EnvCommandBase.EnsureEnvName(); err != nil {
		return err
	}
	switch len(args) {
	case 1:
		c.ServiceName = args[0]
	case 0:
		return errors.New("no service specified")
	}
	if err := cmd.CheckEmpty(args[1:]); err != nil {
		return err
	}
	return c.UnitCommandBase.Init(args)
}

func (c *ResolvedCommand) Init(args []string) error {
	if err := c.EnvCommandBase.EnsureEnvName(); err != nil {
		return err
	}
	if len(args) > 0 {
		c.UnitName = args[0]
		if !names.IsUnit(c.UnitName) {
			return fmt.Errorf("invalid unit name %q", c.UnitName)
		}
		args = args[1:]
	} else {
		return fmt.Errorf("no unit specified")
	}
	return cmd.CheckEmpty(args)
}

func (c *RunCommand) Init(args []string) error {
	if err := c.EnvCommandBase.EnsureEnvName(); err != nil {
		return err
	}
	if len(args) == 0 {
		return errors.New("no commands specified")
	}
	c.commands, args = args[0], args[1:]

	if c.all {
		if len(c.machines) != 0 {
			return fmt.Errorf("You cannot specify --all and individual machines")
		}
		if len(c.services) != 0 {
			return fmt.Errorf("You cannot specify --all and individual services")
		}
		if len(c.units) != 0 {
			return fmt.Errorf("You cannot specify --all and individual units")
		}
	} else {
		if len(c.machines) == 0 && len(c.services) == 0 && len(c.units) == 0 {
			return fmt.Errorf("You must specify a target, either through --all, --machine, --service or --unit")
		}
	}

	var nameErrors []string
	for _, machineId := range c.machines {
		if !names.IsMachine(machineId) {
			nameErrors = append(nameErrors, fmt.Sprintf("  %q is not a valid machine id", machineId))
		}
	}
	for _, service := range c.services {
		if !names.IsService(service) {
			nameErrors = append(nameErrors, fmt.Sprintf("  %q is not a valid service name", service))
		}
	}
	for _, unit := range c.units {
		if !names.IsUnit(unit) {
			nameErrors = append(nameErrors, fmt.Sprintf("  %q is not a valid unit name", unit))
		}
	}
	if len(nameErrors) > 0 {
		return fmt.Errorf("The following run targets are not valid:\n%s",
			strings.Join(nameErrors, "\n"))
	}

	return cmd.CheckEmpty(args)
}