signer name "%s" must start with lowercase alphanumeric char

Error message

signer name "%s" must start with lowercase alphanumeric characters and can include "-" or "_" after the first character

What it means

Error "signer name "%s" must start with lowercase alphanumeric characters and can include "-" or "_" after the first character" thrown in docker/cli.

Source

Thrown at cmd/docker-trust/trust/signer_add.go:53

		RunE: func(cmd *cobra.Command, args []string) error {
			options.signer = args[0]
			options.repos = args[1:]
			return addSigner(cmd.Context(), dockerCLI, options)
		},
		DisableFlagsInUseLine: true,
	}
	flags := cmd.Flags()
	options.keys = opts.NewListOpts(nil)
	flags.Var(&options.keys, "key", "Path to the signer's public key file")
	return cmd
}

var validSignerName = lazyregexp.New(`^[a-z0-9][a-z0-9\_\-]*$`).MatchString

func addSigner(ctx context.Context, dockerCLI command.Cli, options signerAddOptions) error {
	signerName := options.signer
	if !validSignerName(signerName) {
		return fmt.Errorf("signer name \"%s\" must start with lowercase alphanumeric characters and can include \"-\" or \"_\" after the first character", signerName)
	}
	if signerName == "releases" {
		return errors.New("releases is a reserved keyword, use a different signer name")
	}

	if options.keys.Len() == 0 {
		return errors.New("path to a public key must be provided using the `--key` flag")
	}
	signerPubKeys, err := ingestPublicKeys(options.keys.GetSlice())
	if err != nil {
		return err
	}
	var errRepos []string
	for _, repoName := range options.repos {
		_, _ = fmt.Fprintf(dockerCLI.Out(), "Adding signer \"%s\" to %s...\n", signerName, repoName)
		if err := addSignerToRepo(ctx, dockerCLI, signerName, repoName, signerPubKeys); err != nil {
			_, _ = fmt.Fprintln(dockerCLI.Err(), err.Error()+"\n")
			errRepos = append(errRepos, repoName)

View on GitHub (pinned to e9452d6e78)

When it happens

Trigger: Thrown at cmd/docker-trust/trust/signer_add.go:53 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of docker/cli@e9452d6e78 (2026-08-01). Data as JSON: /data/errors/bffe5dbaef8304fa.json. Report an issue: GitHub.