What causes "could not find target %d" in go-delve/delve?

Run 'target list' to see valid target PIDs and pick one from that output.

could not find target

Error message

could not find target %d

What it means

'target switch <pid>' searches the current target group for a live target with the given PID. If no valid target matches, Delve returns 'could not find target %d'. The PID must belong to a currently debugged (followed or attached) process that is still valid.

Solutions

Run 'target list' to see valid target PIDs and pick one from that output.
Verify the child process is still alive; if it exited, re-launch or re-enable follow-exec before the exec occurs.
Check you are not confusing the dlv process PID or a shell PID with the debuggee PID.
If the target should exist but does not, check follow-exec is enabled with a regex matching the child's cmdline.

Example fix

// before (guessed pid)
target switch 99999
// after (use pid from target list)
target list
target switch 4242

Defensive patterns

Strategy: validation

Validate before calling

// query valid targets first via the evaluate command:
out := runEval("target list")
validPids := parsePidsFromList(out) // column 2 of each line
if !validPids[pid] {
    return fmt.Errorf("pid %d not debugged; pick from target list", pid)
}

Prevention

Always source PIDs from 'target list' output
Re-check liveness after child processes exit during follow-exec
Do not confuse dlv's or a shell's PID with the debuggee PID

When it happens

Trigger: Running 'target switch 1234' where 1234 was never debugged, has exited (tgt.Valid() != nil), or belongs to an unrelated process on the system.

Common situations: Trying to switch to a child process that already exited during follow-exec debugging; using the parent shell PID instead of the debuggee PID; stale PID from a previous session; switching while only one target exists and mistyping the PID.

Related errors

AI-assisted analysis of go-delve/delve@a23773e6c3 (2026-08-31). Data as JSON: /api/errors/d643e1aa1d6c14e2. Report an issue: GitHub.

Appendix: source

Thrown at service/dap/command.go:322

			return "", fmt.Errorf("unknown argument %q to 'target follow-exec'", argv[0])
		}
	case "switch": // TODO: This may cause inconsistency between debugger and frontend.
		tgrp, unlock := s.debugger.LockTargetGroup()
		defer unlock()
		pid, err := strconv.Atoi(argv[1])
		if err != nil {
			return "", err
		}
		found := false
		for _, tgt := range tgrp.Targets() {
			if _, err = tgt.Valid(); err == nil && tgt.Pid() == pid {
				found = true
				tgrp.Selected = tgt
				tgt.SwitchThread(pid)
			}
		}
		if !found {
			return "", fmt.Errorf("could not find target %d", pid)
		}
		return fmt.Sprintf("Switched to process %d", pid), err
	default:
		return "", fmt.Errorf("unknown target command")
	}
}

View on GitHub (pinned to a23773e6c3)