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| author | Pádraig Brady <P@draigBrady.com> | 2016-01-11 22:31:45 +0000 |
|---|---|---|
| committer | Pádraig Brady <P@draigBrady.com> | 2016-01-13 11:16:39 +0000 |
| commit | 6ceb7ef87fdf138f0553f32a95567920cc51ae1a (patch) | |
| tree | 05ebd561ad09e7458eeec20fc5dc02a77098fe12 /doc/coreutils.texi | |
| parent | a0c5313d60703c480014bfd810bf8f1cf9903299 (diff) | |
| download | coreutils-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/coreutils.texi')
| -rw-r--r-- | doc/coreutils.texi | 17 |
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 |