Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S941990AbcLWGUW (ORCPT <rfc822;w@1wt.eu>);
        Fri, 23 Dec 2016 01:20:22 -0500
Received: from mail-ua0-f170.google.com ([209.85.217.170]:35688 "EHLO
        mail-ua0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1751150AbcLWGUU (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Fri, 23 Dec 2016 01:20:20 -0500
MIME-Version: 1.0
From: Keno Fischer <keno@juliacomputing.com>
Date: Fri, 23 Dec 2016 01:19:38 -0500
Message-ID: <CABV8kRxLJo=nXXpP-y2YGaPaodahkckLm=o-QTPU9Njkgjpf7g@mail.gmail.com>
Subject: Why do Zombie process' /proc entries have uid 0?
To: linux-kernel@vger.kernel.org
Content-Type: text/plain; charset=UTF-8
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Content-Length: 821
Lines: 32

This is mostly out of curiosity, but I was surprised by the behavior, so
I was hoping somebody might be able to explain why this behavior was
chosen. In particular, consider any zombie process, e.g.

$ cat /proc/77078/status
Name: test
State: Z (zombie)
Tgid: 77078
Ngid: 0
Pid: 77078
PPid: 77077
TracerPid: 0
Uid: 1000 1000 1000 1000
Gid: 1000 1000 1000 1000
[...]

now, this process has uid 1000, as does the /proc/<pid> directory

$ stat /proc/77078
  File: '/proc/77078'
Access: (0555/dr-xr-xr-x)  Uid: ( 1000/    keno)   Gid: ( 1000/    keno)

but most files in /proc/<pid> are owned by root:

$ stat /proc/77078/status
  File: '/proc/77078/status'
Access: (0444/-r--r--r--)  Uid: (    0/    root)   Gid: (    0/    root)

Why is this? Why don't these files remain owned by the same uid as the
process itself?

Keno