git: c362781c8d6a - main - timeout(1): Document the reaper implementation and behaivor

The branch main has been updated by bapt:

URL: https://cgit.FreeBSD.org/src/commit/?id=c362781c8d6a878ac93f3debc45d401bd5296eee

commit c362781c8d6a878ac93f3debc45d401bd5296eee
Author:     Aaron LI <aly@aaronly.me>
AuthorDate: 2025-04-03 02:54:49 +0000
Commit:     Baptiste Daroussin <bapt@FreeBSD.org>
CommitDate: 2025-04-16 19:45:38 +0000

    timeout(1): Document the reaper implementation and behaivor
    
    If timeout(1) runs with the --foreground option, it becomes the reaper
    of the command and its descendants and will wait for all of them to
    terminate.  This behavior is different from the old FreeBSD version and
    GNU version.
    
    For example, if there is a descendant running in the background, like:
    $ timeout -s INT 2 sh -c 'sleep 4 & sleep 5'
    when timeout(1) sends the SIGINT to all descendants, the child 'sh'
    process and the foreground 'sleep 5' process will immediately terminate,
    but the background 'sleep 4' will be reparented to the timeout(1)
    itself.  Because a background process ignores SIGINT and SIGQUIT,
    the whole command completes until the background 'sleep 4' finishes.
    
    In comparison, the old FreeBSD version and GNU version will just
    terminate itself, letting the background 'sleep 4' process be reparented
    to an upper reaper like init.
    
    The POSIX.1-2024 standard doesn't specify the required behavior in such
    cases, so I decided to keep the current implementation.  Nonetheless,
    the updated timeout(1) has changed a lot in order to conform to the
    standard.
    
    Obtained-from: DragonFly BSD
---
 bin/timeout/timeout.1 | 37 +++++++++++++++++++++++++++++++++----
 1 file changed, 33 insertions(+), 4 deletions(-)

diff --git a/bin/timeout/timeout.1 b/bin/timeout/timeout.1
index 43a484dac76f..6486ccf99a36 100644
--- a/bin/timeout/timeout.1
+++ b/bin/timeout/timeout.1
@@ -1,6 +1,7 @@
 .\" SPDX-License-Identifier: BSD-2-Clause
 .\"
 .\" Copyright (c) 2014 Baptiste Daroussin <bapt@FreeBSD.org>
+.\" Copyright (c) 2025 Aaron LI <aly@aaronly.me>
 .\" All rights reserved.
 .\"
 .\" Redistribution and use in source and binary forms, with or without
@@ -101,6 +102,9 @@ The options are as follows:
 Only time out the
 .Ar command
 itself, but do not propagate signals to its descendants.
+See the
+.Sx IMPLEMENTATION NOTES
+section for more details.
 .It Fl k Ar time , Fl -kill-after Ar time
 Send a
 .Dv SIGKILL
@@ -145,6 +149,30 @@ hours
 .It Cm d
 days
 .El
+.Sh IMPLEMENTATION NOTES
+If the
+.Fl -foreground
+option is not specified,
+.Nm
+runs as the reaper (see also
+.Xr procctl 2 )
+of the
+.Ar command
+and its descendants, and will wait for all the descendants to terminate.
+This behavior might cause surprises if there are descendants running
+in the background, because they will ignore
+.Dv SIGINT
+and
+.Dv SIGQUIT
+signals.
+For example, the following command that sends a
+.Dv SIGTERM
+signal will complete in 2 seconds:
+.Dl $ timeout -s TERM 2 sh -c 'sleep 4 & sleep 5'
+However, this command that sends a
+.Dv SIGINT
+signal will complete in 4 seconds:
+.Dl $ timeout -s INT 2 sh -c 'sleep 4 & sleep 5'
 .Sh EXIT STATUS
 If the time limit was reached and the
 .Fl -preserve-status
@@ -247,9 +275,9 @@ The
 command first appeared in
 .Fx 10.3 .
 .Pp
-The
+The initial
 .Fx
-work is compatible with GNU
+work was compatible with GNU
 .Nm
 by
 .An Padraig Brady ,
@@ -258,6 +286,7 @@ The
 .Nm
 utility first appeared in GNU Coreutils 7.0.
 .Sh AUTHORS
-.An Baptiste Daroussin Aq Mt bapt@FreeBSD.org
-and
+.An Baptiste Daroussin Aq Mt bapt@FreeBSD.org ,
 .An Vsevolod Stakhov Aq Mt vsevolod@FreeBSD.org
+and
+.An Aaron LI Aq Mt aly@aaronly.me