From 1efce5663554619db34d2722be7d6e5a14404065 Mon Sep 17 00:00:00 2001 From: Paul Eggert Date: Wed, 6 Jul 2022 23:42:19 -0500 Subject: [PATCH] dd: doc improvement (Bug#54586) * doc/coreutils.texi (dd invocation): Explain fdatasync and fsync better. --- doc/coreutils.texi | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) diff --git a/doc/coreutils.texi b/doc/coreutils.texi index 7bca37b71..e0c87d1ad 100644 --- a/doc/coreutils.texi +++ b/doc/coreutils.texi @@ -9466,7 +9466,13 @@ Continue after read errors. @cindex synchronized data writes, before finishing Synchronize output data just before finishing, even if there were write errors. -This forces a physical write of output data. +This forces a physical write of output data, +so that even if power is lost the output data will be preserved. +If neither this nor @samp{fsync} are specified, output is treated as +usual with file systems, i.e., output data and metadata may be cached +in primary memory for some time before the operating system physically +writes it, and thus output data and metadata may be lost if power is lost. +@xref{sync invocation}. This conversion is a GNU extension to POSIX. @item fsync @@ -9474,7 +9480,10 @@ This conversion is a GNU extension to POSIX. @cindex synchronized data and metadata writes, before finishing Synchronize output data and metadata just before finishing, even if there were write errors. -This forces a physical write of output data and metadata. +This acts like @samp{fdatasync} except it also preserves output metadata, +such as the last-modified time of the output file; for this reason it +may be a bit slower than @samp{fdatasync} although the performance +difference is typically insignificant for @command{dd}. This conversion is a GNU extension to POSIX. @end table -- 2.36.1