Re: Unit of /proc/sys/kernel/random/poolsize
From: Michael Kerrisk (man-pages) <hidden>
Date: 2015-12-17 07:51:57
Subsystem:
the rest · Maintainer:
Linus Torvalds
Possibly related (same subject, not in this thread)
- 2015-12-20 · Re: Unit of /proc/sys/kernel/random/poolsize · Michael Kerrisk (man-pages) <hidden>
- 2015-12-17 · Re: Unit of /proc/sys/kernel/random/poolsize · walter harms <hidden>
- 2011-10-22 · Unit of /proc/sys/kernel/random/poolsize · Tom Gundersen <hidden>
Hello Tom, On 10/22/2011 02:13 PM, Tom Gundersen wrote:
Hi, This might not be so much a bug report, as a request for clarification. In random(4) it is explained that /proc/sys/kernel/random/poolsize contains the value in bits or bytes in >=2.6 and 2.4 respectively. However, the example in the preceding paragraph assumes a 2.4 kernel is being used, and treats the value as if it were in bytes. I ran across this as I maintain the initscripts for Arch Linux, where we have been (mistakenly) following the example even though we use a 3.0 kernel. Maybe it would be worthwhile to change the example into the 2.6 interface, or at least include a word of caution? I realise that using a value which is too large, probably does no harm at all, but not being cryptography expert, I'd rather not take the chance.
Long after the fact... I applied the patch below. Okay? Thanks for the report. Cheers, Michael PS I am going to be in Oslo a couple of times in coming months. Perhaps we could meet up for a beer or so.
diff --git a/man4/random.4 b/man4/random.4
index 2519981..4a32aac 100644
--- a/man4/random.4
+++ b/man4/random.4@@ -171,7 +171,7 @@ This reduces the actual amount of noise in the entropy pool below the estimate. In order to counteract this effect, it helps to carry entropy pool information across shut-downs and start-ups. -To do this, add the following lines to an appropriate script +To do this, add the lines to an appropriate script which is run during the Linux system start-up sequence: .nf
@@ -186,7 +186,8 @@ which is run during the Linux system start-up sequence: fi chmod 600 $random_seed poolfile=/proc/sys/kernel/random/poolsize - [ \-r $poolfile ] && bytes=\`cat $poolfile\` || bytes=512 + [ \-r $poolfile ] && bits=\`cat $poolfile\` || bits=4096 + bytes=$(expr $bits / 8) dd if=/dev/urandom of=$random_seed count=1 bs=$bytes .fi
@@ -201,9 +202,14 @@ run during the Linux system shutdown: touch $random_seed chmod 600 $random_seed poolfile=/proc/sys/kernel/random/poolsize - [ \-r $poolfile ] && bytes=\`cat $poolfile\` || bytes=512 + [ \-r $poolfile ] && bits=\`cat $poolfile\` || bits=4096 + bytes=$(expr $bits / 8) dd if=/dev/urandom of=$random_seed count=1 bs=$bytes .fi + +In the above examples, we assume Linux 2.6.0 or later, where +.IR /proc/sys/kernel/random/poolsize +returns the size of the entropy pool in bits (see below). .SS /proc Interface The files in the directory .I /proc/sys/kernel/random
--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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