caddyserver/caddy · error

invalid filename for log file: %v

Error message

invalid filename for log file: %v

What it means

Error "invalid filename for log file: %v" thrown in caddyserver/caddy.

Source

Thrown at modules/logging/filewriter.go:166

	// <format> must be a Go time compatible format, see https://pkg.go.dev/time#pkg-constants
	BackupTimeFormat string `json:"backup_time_format,omitempty"`
}

// CaddyModule returns the Caddy module information.
func (FileWriter) CaddyModule() caddy.ModuleInfo {
	return caddy.ModuleInfo{
		ID:  "caddy.logging.writers.file",
		New: func() caddy.Module { return new(FileWriter) },
	}
}

// Provision sets up the module
func (fw *FileWriter) Provision(ctx caddy.Context) error {
	// Replace placeholder in filename
	repl := caddy.NewReplacer()
	filename, err := repl.ReplaceOrErr(fw.Filename, true, true)
	if err != nil {
		return fmt.Errorf("invalid filename for log file: %v", err)
	}

	fw.Filename = filename
	return nil
}

func (fw FileWriter) String() string {
	fpath, err := caddy.FastAbs(fw.Filename)
	if err == nil {
		return fpath
	}
	return fw.Filename
}

// WriterKey returns a unique key representing this fw.
func (fw FileWriter) WriterKey() string {
	return "file:" + fw.Filename
}

View on GitHub (pinned to 50e54ee279)

Solutions

1. Provide a valid, writable file path for the log file; the wrapped error explains why the name is invalid.

When it happens

Trigger: Thrown at modules/logging/filewriter.go:166 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of caddyserver/caddy@50e54ee279 (2026-08-15). Data as JSON: /api/errors/7570d332cd4efada. Report an issue: GitHub.