user_namespaces.7: Document maximum nesting depth for user namespaces

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

diff --git a/man7/user_namespaces.7 b/man7/user_namespaces.7
index 46b4e47a8e0ab5a2b981ea08127b32f6b324b92f..04081e2fc32c97672f46310781bf84d7f902d856 100644 (file)
--- a/man7/user_namespaces.7
+++ b/man7/user_namespaces.7
@@ -63,6 +63,17 @@ with the
 .BR CLONE_NEWUSER
 flag.
 
+The kernel imposes (since version 3.11) a limit of 32 nested levels of
+.\" commit 8742f229b635bf1c1c84a3dfe5e47c814c20b5c8
+user namespaces.
+.\" FIXME Explain the rationale for this limit. (What is the rationale?)
+Calls to
+.BR unshare (2)
+or
+.BR clone (2)
+that would cause this limit to be exceeded fail with the error
+.BR EUSERS .
+
 Each process is a member of exactly one user namespace.
 A process created via
 .BR fork (2)