git: 5119386711a8 - stable/13 - sync.8: Document that the "sync dance" is not a thing

The branch stable/13 has been updated by 0mp:

URL: https://cgit.FreeBSD.org/src/commit/?id=5119386711a88f86dfb3ec3eb609d0d2c6a4f050

commit 5119386711a88f86dfb3ec3eb609d0d2c6a4f050
Author:     Mateusz Piotrowski <0mp@FreeBSD.org>
AuthorDate: 2024-04-23 14:12:45 +0000
Commit:     Mateusz Piotrowski <0mp@FreeBSD.org>
CommitDate: 2024-04-28 18:29:36 +0000

    sync.8: Document that the "sync dance" is not a thing
    
    People still believe that it is essential to run sync(8) a couple of
    times before a reboot/halt. Document that this has not been necessary
    for a long time now.
    
    Reviewed by:    imp, bcr, Pau Amma <pauamma@gundo.com>
    MFC after:      3 days
    Differential Revision:  https://reviews.freebsd.org/D33233
    
    (cherry picked from commit 177ba183076bd6fe6b29b1d657b954cca256506b)
---
 bin/sync/sync.8 | 30 +++++++++++++++++++++++++++++-
 1 file changed, 29 insertions(+), 1 deletion(-)

diff --git a/bin/sync/sync.8 b/bin/sync/sync.8
index 732d813880e2..222e9edf59f9 100644
--- a/bin/sync/sync.8
+++ b/bin/sync/sync.8
@@ -28,7 +28,7 @@
 .\"
 .\"	@(#)sync.8	8.1 (Berkeley) 5/31/93
 .\"
-.Dd May 31, 1993
+.Dd April 25, 2024
 .Dt SYNC 8
 .Os
 .Sh NAME
@@ -71,3 +71,31 @@ A
 .Nm
 utility appeared in
 .At v4 .
+.Pp
+On systems older than
+.Bx 4.0 ,
+commands like
+.Xr reboot 8
+and
+.Xr halt 8
+were unavailable.
+The shutdown procedure involved running
+.Nm ,
+waiting for the lights to stop,
+and turning off the machine.
+.Pp
+Issuing three separate
+.Nm
+commands (one line each) was a placebo that would generally suffice in
+.At v7
+machines that were otherwise quiesced systems.
+It replaced the one-per-line
+.Nm
+as a substitute for waiting.
+.Pp
+.Bx 4.0
+introduced
+.Xr reboot 2
+and
+.Xr sync 2
+which rendered this trick obsolete.