GNU bug report logs - #19995
doc: Adds a bug section to sync.1 page to draw attention to unexpected behavior allowed by POSIX.

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: saulery <at> free.fr
Subject: bug#19995: closed (Re: bug#19995: [patch] sync.1: prevent data
 loss (reposte of my previous merged message))
Date: Thu, 05 Mar 2015 12:24:02 +0000

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Your bug report

#19995: doc: Adds a bug section to sync.1 page to draw attention to unexpected behavior allowed by POSIX.

which was filed against the coreutils package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to 19995 <at> debbugs.gnu.org.

-- 
19995: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=19995
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

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From: Pádraig Brady <P <at> draigBrady.com>
To: Stéphane Aulery <saulery <at> free.fr>,
 19995-done <at> debbugs.gnu.org
Subject: Re: bug#19995: [patch] sync.1: prevent data loss (reposte of my
 previous merged message)
Date: Thu, 05 Mar 2015 12:23:44 +0000

On 05/03/15 11:45, Stéphane Aulery wrote:
> Hello,
> 
> A Debian user reported [1] that sync.1 man page is incomplete unlike sync.2
> There is no mention of the unexpected behavior allowed by POSIX, which can
> cause data loss.
> 
> This patch provides a possible correction.
> 
> [1] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=507085

How about I apply this in your name instead?

diff --git a/man/sync.x b/man/sync.x
index 79fee22..18ee3fc 100644
--- a/man/sync.x
+++ b/man/sync.x
@@ -2,5 +2,8 @@
 sync \- Synchronize cached writes to persistent storage
 [DESCRIPTION]
 .\" Add any additional description here
+[BUGS]
+Persistence guarantees vary per system.
+See the system calls below for more details.
 [SEE ALSO]
 fdatasync(2), fsync(2), sync(2), syncfs(2)

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From: saulery <at> free.fr
To: bug-coreutils <at> gnu.org
Cc: Stéphane Aulery <saulery <at> free.fr>
Subject: doc: Adds a bug section to sync.1 page to draw attention to
 unexpected behavior allowed by POSIX.
Date: Wed,  4 Mar 2015 01:06:01 +0100

From: Stéphane Aulery <saulery <at> free.fr>

Almost identical copy of sync.2.

Debian bug #507085 reported by jidanni <at> jidanni.org

Signed-off-by: Stéphane Aulery <saulery <at> free.fr>
---
 man/sync.x | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/man/sync.x b/man/sync.x
index 79fee22..5b85bba 100644
--- a/man/sync.x
+++ b/man/sync.x
@@ -2,5 +2,10 @@
 sync \- Synchronize cached writes to persistent storage
 [DESCRIPTION]
 .\" Add any additional description here
+[BUGS]
+According to the standard specification (e.g., POSIX.1-2001), sync()
+syscall schedules the writes, but may return before the actual writing is
+done. However, since version 1.3.20 Linux does actually wait. (This still
+does not guarantee data integrity: modern disks have large caches.)
 [SEE ALSO]
 fdatasync(2), fsync(2), sync(2), syncfs(2)
-- 
2.1.4

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