From 649781df84faee5e02356c6c47883d958495098e Mon Sep 17 00:00:00 2001
From: Andrew Lytvynov <awly@tailscale.com>
Date: Mon, 27 Apr 2026 09:25:46 -0700
Subject: [PATCH] util/pidowner: remove unused package (#19521)

Added in 2020, this appears to be unused.

Updates #cleanup

Signed-off-by: Andrew Lytvynov <awly@tailscale.com>
---
 util/pidowner/pidowner.go         | 24 ---------------
 util/pidowner/pidowner_linux.go   | 36 ----------------------
 util/pidowner/pidowner_noimpl.go  |  8 -----
 util/pidowner/pidowner_test.go    | 50 -------------------------------
 util/pidowner/pidowner_windows.go | 35 ----------------------
 5 files changed, 153 deletions(-)
 delete mode 100644 util/pidowner/pidowner.go
 delete mode 100644 util/pidowner/pidowner_linux.go
 delete mode 100644 util/pidowner/pidowner_noimpl.go
 delete mode 100644 util/pidowner/pidowner_test.go
 delete mode 100644 util/pidowner/pidowner_windows.go

diff --git a/util/pidowner/pidowner.go b/util/pidowner/pidowner.go
deleted file mode 100644
index cec92ba36..000000000
--- a/util/pidowner/pidowner.go
+++ /dev/null
@@ -1,24 +0,0 @@
-// Copyright (c) Tailscale Inc & contributors
-// SPDX-License-Identifier: BSD-3-Clause
-
-// Package pidowner handles lookups from process ID to its owning user.
-package pidowner
-
-import (
-	"errors"
-	"runtime"
-)
-
-var ErrNotImplemented = errors.New("not implemented for GOOS=" + runtime.GOOS)
-
-var ErrProcessNotFound = errors.New("process not found")
-
-// OwnerOfPID returns the user ID that owns the given process ID.
-//
-// The returned user ID is suitable to passing to os/user.LookupId.
-//
-// The returned error will be ErrNotImplemented for operating systems where
-// this isn't supported.
-func OwnerOfPID(pid int) (userID string, err error) {
-	return ownerOfPID(pid)
-}
diff --git a/util/pidowner/pidowner_linux.go b/util/pidowner/pidowner_linux.go
deleted file mode 100644
index f3f5cd97d..000000000
--- a/util/pidowner/pidowner_linux.go
+++ /dev/null
@@ -1,36 +0,0 @@
-// Copyright (c) Tailscale Inc & contributors
-// SPDX-License-Identifier: BSD-3-Clause
-
-package pidowner
-
-import (
-	"fmt"
-	"os"
-	"strings"
-
-	"tailscale.com/util/lineiter"
-)
-
-func ownerOfPID(pid int) (userID string, err error) {
-	file := fmt.Sprintf("/proc/%d/status", pid)
-	for lr := range lineiter.File(file) {
-		line, err := lr.Value()
-		if err != nil {
-			if os.IsNotExist(err) {
-				return "", ErrProcessNotFound
-			}
-			return "", err
-		}
-		if len(line) < 4 || string(line[:4]) != "Uid:" {
-			continue
-		}
-		f := strings.Fields(string(line))
-		if len(f) >= 2 {
-			userID = f[1] // real userid
-		}
-	}
-	if userID == "" {
-		return "", fmt.Errorf("missing Uid line in %s", file)
-	}
-	return userID, nil
-}
diff --git a/util/pidowner/pidowner_noimpl.go b/util/pidowner/pidowner_noimpl.go
deleted file mode 100644
index 4bc665d61..000000000
--- a/util/pidowner/pidowner_noimpl.go
+++ /dev/null
@@ -1,8 +0,0 @@
-// Copyright (c) Tailscale Inc & contributors
-// SPDX-License-Identifier: BSD-3-Clause
-
-//go:build !windows && !linux
-
-package pidowner
-
-func ownerOfPID(pid int) (userID string, err error) { return "", ErrNotImplemented }
diff --git a/util/pidowner/pidowner_test.go b/util/pidowner/pidowner_test.go
deleted file mode 100644
index 2774a8ab0..000000000
--- a/util/pidowner/pidowner_test.go
+++ /dev/null
@@ -1,50 +0,0 @@
-// Copyright (c) Tailscale Inc & contributors
-// SPDX-License-Identifier: BSD-3-Clause
-
-package pidowner
-
-import (
-	"math/rand"
-	"os"
-	"os/user"
-	"testing"
-)
-
-func TestOwnerOfPID(t *testing.T) {
-	id, err := OwnerOfPID(os.Getpid())
-	if err == ErrNotImplemented {
-		t.Skip(err)
-	}
-	if err != nil {
-		t.Fatal(err)
-	}
-	t.Logf("id=%q", id)
-
-	u, err := user.LookupId(id)
-	if err != nil {
-		t.Fatalf("LookupId: %v", err)
-	}
-	t.Logf("Got: %+v", u)
-}
-
-// validate that OS implementation returns ErrProcessNotFound.
-func TestNotFoundError(t *testing.T) {
-	// Try a bunch of times to stumble upon a pid that doesn't exist...
-	const tries = 50
-	for range tries {
-		_, err := OwnerOfPID(rand.Intn(1e9))
-		if err == ErrNotImplemented {
-			t.Skip(err)
-		}
-		if err == nil {
-			// We got unlucky and this pid existed. Try again.
-			continue
-		}
-		if err == ErrProcessNotFound {
-			// Pass.
-			return
-		}
-		t.Fatalf("Error is not ErrProcessNotFound: %T %v", err, err)
-	}
-	t.Errorf("after %d tries, couldn't find a process that didn't exist", tries)
-}
diff --git a/util/pidowner/pidowner_windows.go b/util/pidowner/pidowner_windows.go
deleted file mode 100644
index 8edd7698d..000000000
--- a/util/pidowner/pidowner_windows.go
+++ /dev/null
@@ -1,35 +0,0 @@
-// Copyright (c) Tailscale Inc & contributors
-// SPDX-License-Identifier: BSD-3-Clause
-
-package pidowner
-
-import (
-	"fmt"
-	"syscall"
-
-	"golang.org/x/sys/windows"
-)
-
-func ownerOfPID(pid int) (userID string, err error) {
-	procHnd, err := windows.OpenProcess(windows.PROCESS_QUERY_INFORMATION, false, uint32(pid))
-	if err == syscall.Errno(0x57) { // invalid parameter, for PIDs that don't exist
-		return "", ErrProcessNotFound
-	}
-	if err != nil {
-		return "", fmt.Errorf("OpenProcess: %T %#v", err, err)
-	}
-	defer windows.CloseHandle(procHnd)
-
-	var tok windows.Token
-	if err := windows.OpenProcessToken(procHnd, windows.TOKEN_QUERY, &tok); err != nil {
-		return "", fmt.Errorf("OpenProcessToken: %w", err)
-	}
-
-	tokUser, err := tok.GetTokenUser()
-	if err != nil {
-		return "", fmt.Errorf("GetTokenUser: %w", err)
-	}
-
-	sid := tokUser.User.Sid
-	return sid.String(), nil
-}