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authorPádraig Brady <P@draigBrady.com>2016-01-11 22:31:45 +0000
committerPádraig Brady <P@draigBrady.com>2016-01-13 11:16:39 +0000
commit6ceb7ef87fdf138f0553f32a95567920cc51ae1a (patch)
tree05ebd561ad09e7458eeec20fc5dc02a77098fe12 /doc
parenta0c5313d60703c480014bfd810bf8f1cf9903299 (diff)
downloadcoreutils-6ceb7ef87fdf138f0553f32a95567920cc51ae1a.tar.xz
doc: suggest dd "sync" flag to maximize "nocache" effectiveness
doc/coreutils.texi (dd invocation): Add oflag=sync to the streaming example. Also reference the "direct" flag. Mention this is only a request to the system. * src/dd.c (usage): Mention the "sync" flag along with "nocache". Also mention that it's only a request to drop the cache. * THANKS.in: Add reporter Francois Rigault.
Diffstat (limited to 'doc')
-rw-r--r--doc/coreutils.texi17
1 files changed, 12 insertions, 5 deletions
diff --git a/doc/coreutils.texi b/doc/coreutils.texi
index eb5159a44..01791be5b 100644
--- a/doc/coreutils.texi
+++ b/doc/coreutils.texi
@@ -8677,12 +8677,18 @@ Use synchronized I/O for both data and metadata.
@item nocache
@opindex nocache
@cindex discarding file cache
-Discard the data cache for a file.
-When count=0 all cache is discarded,
+Request to discard the system data cache for a file.
+When count=0 all cached data for the file is specified,
otherwise the cache is dropped for the processed
-portion of the file. Also when count=0
+portion of the file. Also when count=0,
failure to discard the cache is diagnosed
and reflected in the exit status.
+
+Note data that is not already persisted to storage will not
+be discarded from cache, so note the use of the ``sync'' options
+in the examples below, which are used to maximize the
+effectiveness of the @samp{nocache} flag.
+
Here are some usage examples:
@example
@@ -8695,8 +8701,9 @@ dd of=ofile oflag=nocache conv=notrunc,fdatasync count=0
# Drop cache for part of file
dd if=ifile iflag=nocache skip=10 count=10 of=/dev/null
-# Stream data using just the read-ahead cache
-dd if=ifile of=ofile iflag=nocache oflag=nocache
+# Stream data using just the read-ahead cache.
+# See also the @samp{direct} flag.
+dd if=ifile of=ofile iflag=nocache oflag=nocache,sync
@end example
@item nonblock