What causes "could not read auxiliary vector: %v" in go-delve/delve?

Ensure the target process is still alive when attaching (use ps -p immediately before dlv attach).

could not read auxiliary vector: %v

Error message

could not read auxiliary vector: %v

What it means

nativeProcess.EntryPoint reads /proc/<pid>/auxv via os.ReadFile to locate the dynamic loader's entry point, which is required to debug PIE (position-independent) executables. If the auxv file cannot be read (e.g. the process has exited and /proc/<pid> is gone, or permission is denied), the error is wrapped and returned. Without auxv, Delve cannot compute the entry point and cannot properly initialize the debug session for PIE binaries.

Source

Thrown at pkg/proc/native/proc_linux.go:939

		return nil
	}
	// For some reason the process will sometimes enter stopped state after a
	// detach, this doesn't happen immediately either.
	// We have to wait a bit here, then check if the main thread is stopped and
	// SIGCONT it if it is.
	time.Sleep(50 * time.Millisecond)
	if s := status(dbp.pid, dbp.os.comm); s == 'T' {
		_ = sys.Kill(dbp.pid, sys.SIGCONT)
	}
	return nil
}

// EntryPoint will return the process entry point address, useful for
// debugging PIEs.
func (dbp *nativeProcess) EntryPoint() (uint64, error) {
	auxvbuf, err := os.ReadFile(fmt.Sprintf("/proc/%d/auxv", dbp.pid))
	if err != nil {
		return 0, fmt.Errorf("could not read auxiliary vector: %v", err)
	}

	return linutil.EntryPointFromAuxv(auxvbuf, dbp.bi.Arch.PtrSize()), nil
}

func (dbp *nativeProcess) SetUProbe(fnName string, goidOffset int64, args []ebpf.UProbeArgMap) error {
	// Lazily load and initialize the BPF program upon request to set a uprobe.
	if dbp.os.ebpf == nil {
		var err error
		dbp.os.ebpf, err = ebpf.LoadEBPFTracingProgram(dbp.bi.Images[0].Path)
		if err != nil {
			return err
		}
	}

	// We only allow up to 12 args for a BPF probe.
	// 6 inputs + 6 outputs.
	// Return early if we have more.

View on GitHub (pinned to a23773e6c3)

Solutions

Ensure the target process is still alive when attaching (use ps -p <pid> immediately before dlv attach).
Fix permissions: run dlv as the same user as the target or with sufficient capabilities (CAP_SYS_PTRACE in containers).
Lower /proc/sys/kernel/yama/ptrace_scope (e.g. echo 0 | sudo tee /proc/sys/kernel/yama/ptrace_scope) if it blocks access.
If using containers, launch with docker run --cap-add=SYS_PTRACE --security-opt seccomp=unconfined.

Example fix

// before: attach races with process exit
cmd.Start()
dlv.Attach(pid) // process may already be gone
// after: wait for readiness before attaching
cmd.Start()
for !portReady("127.0.0.1:4040") { time.Sleep(50 * time.Millisecond) }
dlv.Attach(pid)

Defensive patterns

Strategy: validation

Validate before calling

// verify auxv readability before starting a PIE debug session
if _, err := os.ReadFile(fmt.Sprintf("/proc/%d/auxv", pid)); err != nil {
    return fmt.Errorf("cannot access auxv for pid %d: %w", pid, err)
}
// also verify process is alive
if _, err := os.Stat(fmt.Sprintf("/proc/%d", pid)); err != nil {
    return fmt.Errorf("process %d not running", pid)
}

Try / catch

_, err := debugger.Attach(pid)
if err != nil && strings.Contains(err.Error(), "could not read auxiliary vector") {
    // check whether the process died or permissions are insufficient
    if _, statErr := os.Stat(fmt.Sprintf("/proc/%d/auxv", pid)); statErr != nil {
        // process gone: restart it and re-attach
    } else {
        // permission problem: elevate capabilities or fix ptrace_scope
    }
}

Prevention

Confirm the target process is alive before dlv attach
Run dlv as the same user as the target, or add CAP_SYS_PTRACE in containers
Avoid hidepid /proc mounts or run as root when they are required
Set kernel.yama.ptrace_scope appropriately on hardened systems

When it happens

Trigger: Calling EntryPoint (internally during launch/attach initialization of a PIE binary) when /proc/<pid>/auxv cannot be opened: process already terminated, insufficient permissions, or the pid no longer exists.

Common situations: Attaching to a process that exits during startup; running dlv inside a container without CAP_SYS_PTRACE targeting a different user's process; hidepid mount option on /proc restricting visibility of other users' processes; kernel hardening (ptrace_scope=2/3).

Related errors

AI-assisted analysis of go-delve/delve@a23773e6c3 (2026-08-31). Data as JSON: /api/errors/435b2f301963a1bd. Report an issue: GitHub.