[PATCH 2/2] Manual pages: unshare.1: clarify that --pid=<file> requires --fork

["Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>]

Attempting to create a persistent PID namespace with --pid=<file>
will result in an error if --fork is not also specified. Let's
warn people about that, so they don't get puzzled.

Signed-off-by: Michael Kerrisk (man-pages) <mtk.manpages@gmail.com>
---
 sys-utils/unshare.1 | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/sys-utils/unshare.1 b/sys-utils/unshare.1
index 443aac658..7899db3ad 100644
--- a/sys-utils/unshare.1
+++ b/sys-utils/unshare.1
@@ -114,8 +114,13 @@ Unshare the network namespace.  If \fIfile\fP is specified, then a persistent
 namespace is created by a bind mount.
 .TP
 .BR \-p , " \-\-pid" [ =\fIfile ]
-Unshare the PID namespace.  If \fIfile\fP is specified then persistent
-namespace is created by a bind mount.  See also the \fB\-\-fork\fP and
+Unshare the PID namespace.  If \fIfile\fP is specified, then a persistent
+namespace is created by a bind mount.
+(Creation of a persistent PID namespace will fail if the
+.B \-\-fork
+is not also specified.)
+.IP
+See also the \fB\-\-fork\fP and
 \fB\-\-mount-proc\fP options.
 .TP
 .BR \-u , " \-\-uts" [ =\fIfile ]
-- 
2.26.2