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authorJim Meyering <meyering@redhat.com>2011-01-17 11:32:35 +0100
committerJim Meyering <meyering@redhat.com>2011-01-17 19:16:43 +0100
commit0f9cf6b545aa07d552538735182007ae240d6071 (patch)
treeb398d6e5ac331c68ef02b8a870e2b786c4d95aeb
parentbdaef0686fabc1900c4b3686de17a3ffd9f4d847 (diff)
downloadcoreutils-0f9cf6b545aa07d552538735182007ae240d6071.tar.xz
doc: show how to shred more efficiently
* doc/coreutils.texi (shred invocation): Give an example showing how to invoke shred in single-pass mode, and warn that -n0 --zero may be inadequate.
-rw-r--r--doc/coreutils.texi14
1 files changed, 14 insertions, 0 deletions
diff --git a/doc/coreutils.texi b/doc/coreutils.texi
index 9c3e2ed67..8a1b3b62c 100644
--- a/doc/coreutils.texi
+++ b/doc/coreutils.texi
@@ -8892,6 +8892,20 @@ your hard disk, you could give a command like this:
shred --verbose /dev/sda5
@end example
+On modern disks, a single pass should be adequate,
+and it will take one third the time of the default three-pass approach.
+
+@example
+# 1 pass, write pseudo-random data; 3x faster than the default
+shred --verbose -n1 /dev/sda5
+@end example
+
+To be on the safe side, use at least one pass that overwrites using
+pseudo-random data. I.e., don't be tempted to use @samp{-n0 --zero},
+in case some disk controller optimizes the process of writing blocks
+of all zeros, and thereby does not clear all bytes in a block.
+Some SSDs may do just that.
+
A @var{file} of @samp{-} denotes standard output.
The intended use of this is to shred a removed temporary file.
For example: