caddyserver/caddy · error

starting caddy process: %v

Error message

starting caddy process: %v

What it means

Returned by `caddy start` when cmd.Start() fails to launch the detached child `caddy run` process. This is an exec-level failure: binary not found, exec permission denied, or fork failure — before any config logic runs. The error usually wraps errno-level detail (no such file or directory, permission denied).

Source

Thrown at cmd/commandfuncs.go:127

	if err != nil {
		return caddy.ExitCodeFailedStartup,
			fmt.Errorf("generating random confirmation bytes: %v", err)
	}

	// begin writing the confirmation bytes to the child's
	// stdin; use a goroutine since the child hasn't been
	// started yet, and writing synchronously would result
	// in a deadlock
	go func() {
		_, _ = stdinPipe.Write(expect)
		stdinPipe.Close()
	}()

	// start the process
	err = cmd.Start()
	if err != nil {
		return caddy.ExitCodeFailedStartup,
			fmt.Errorf("starting caddy process: %v", err)
	}

	// there are two ways we know we're done: either
	// the process will connect to our listener, or
	// it will exit with an error
	success, exit := make(chan struct{}), make(chan error)

	// in one goroutine, we await the success of the child process
	go func() {
		for {
			conn, err := ln.Accept()
			if err != nil {
				if !errors.Is(err, net.ErrClosed) {
					log.Println(err)
				}
				break
			}
			err = handlePingbackConn(conn, expect)

View on GitHub (pinned to 50e54ee279)

Solutions

1. Verify the binary is executable and on PATH: which caddy && caddy version
2. In containers, raise PID limits (--pids-limit or orchestrator equivalent)
3. Ensure the binary is not on a noexec mount (remount or move it)
4. If wrapper scripts alter argv, invoke the binary by its absolute path

Example fix

# before
caddy start  # starting caddy process: fork: retry: Resource temporarily unavailable
# after
docker run --pids-limit=512 ... caddy start

// verify the binary is startable before daemonizing
bin, err := exec.LookPath("caddy")
if err != nil { return fmt.Errorf("caddy not on PATH: %w", err) }
if _, err := os.Stat(bin); err != nil || os.Getenv("" ) != "" { _ = bin }
out, err := exec.Command(bin, "version").Output()
if err != nil { return fmt.Errorf("cannot execute %s: %w", bin, err) }

if err != nil && strings.Contains(err.Error(), "starting caddy process") {
    if strings.Contains(err.Error(), "no such file") { /* fix PATH / binary path */ }
    if strings.Contains(err.Error(), "resource temporarily unavailable") { /* raise pids-limit */ }
}

When it happens

Trigger: Starting caddy through a wrapper that mangles os.Args[0]; the binary moved or was deleted mid-script; PATH issues when caddy is invoked via a symlink chain; fork blocked by PID limits (fork: retry: Resource temporarily unavailable) in containers.

Common situations: Containers with a PID namespace limit (docker --pids-limit) where the extra child process cannot be forked; scripts that overwrite/move the binary during upgrade; exec'ing from a mounted volume with noexec.

Related errors

• creating stdin pipe: %v
• reading envfile flag: %v
• opening listener for success confirmation: %v
• generating random confirmation bytes: %v
• caddy process exited with error: %v

AI-assisted analysis of caddyserver/caddy@50e54ee279 (2026-08-15). Data as JSON: /api/errors/5d9bdc5a1de1d7b4. Report an issue: GitHub.