linux-kernel - [PATCH] clone.2: Mention that CLONE

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Date:   Wed, 20 Nov 2019 11:45:04 +0100
From:   Christian Brauner <christian@...uner.io>
To:     mtk.manpages@...il.com
Cc:     adrian@...as.de, akpm@...ux-foundation.org, arnd@...db.de,
        avagin@...il.com, christian.brauner@...ntu.com,
        dhowells@...hat.com, fweimer@...hat.com, jannh@...gle.com,
        keescook@...omium.org, linux-api@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-man@...r.kernel.org,
        mingo@...e.hu, oleg@...hat.com, xemul@...tuozzo.com
Subject: [PATCH] clone.2: Mention that CLONE_PARENT is off-limits for inits

From: Christian Brauner <christian.brauner@...ntu.com>

The CLONE_PARENT flag cannot but used by init processes. Let's mention
this in the manpages to prevent suprises.

Signed-off-by: Christian Brauner <christian.brauner@...ntu.com>
---
 man2/clone.2 | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/man2/clone.2 b/man2/clone.2
index f0f29d6f1..aa98ab79b 100644
--- a/man2/clone.2
+++ b/man2/clone.2
@@ -646,6 +646,13 @@ if
 .B CLONE_PARENT
 is set, then the parent of the calling process, rather than the
 calling process itself, will be signaled.
+.IP
+The kernel will not allow global init and init processes in pid
+namespaces to use the
+.B CLONE_PARENT
+flag. This is done to prevent the creation of multi-rooted process
+trees. It also avoids unreapable zombies in the initial pid
+namespace.
 .TP
 .BR CLONE_PARENT_SETTID " (since Linux 2.5.49)"
 Store the child thread ID at the location pointed to by
-- 
2.24.0