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| -rw-r--r-- | man4/random.4 | 63 |
1 files changed, 62 insertions, 1 deletions
diff --git a/man4/random.4 b/man4/random.4 index 9a13c89a..e835720d 100644 --- a/man4/random.4 +++ b/man4/random.4 @@ -16,9 +16,13 @@ .\" Add a Usage subsection that recommends most users to use .\" /dev/urandom, and emphasizes parsimonious usage of /dev/random. .\" -.TH RANDOM 4 2010-08-29 "Linux" "Linux Programmer's Manual" +.TH RANDOM 4 2013-02-17 "Linux" "Linux Programmer's Manual" .SH NAME random, urandom \- kernel random number source devices +.SH SYNOPSIS +#include <linux/random.h> +.sp +.BI "int ioctl(" fd ", RND" request ", " param ");" .SH DESCRIPTION The character special files \fI/dev/random\fP and \fI/dev/urandom\fP (present since Linux 1.3.30) @@ -51,6 +55,12 @@ literature, but it is theoretically possible that such an attack may exist. If this is a concern in your application, use \fI/dev/random\fP instead. +.LP +Writing to \fI/dev/random\fP or \fI/dev/urandom\fP will update the +entropy pool with the data written, but this will not result in a +higher entropy count. This means that it will impact the contents +read from both files but it will not make reads from +\fI/dev/random\fP faster. .SS Usage If you are unsure about whether you should use .IR /dev/random @@ -208,6 +218,57 @@ and contain random strings like 6fd5a44b-35f4-4ad4-a9b9-6b9be13e1fe9. The former is generated afresh for each read, the latter was generated once. +.SS ioctl(2) interface +The following +.BR ioctl (2) +requests are defined on file descriptors connected to either \fI/dev/random\fP +or \fI/dev/urandom\fP. All requests performed will interact with the input +entropy pool impacting both \fI/dev/random\fP and \fI/dev/urandom\fP. +The +.B CAP_SYS_ADMIN +capability is required for all requests except +.B RNDGETENTCNT. +.TP +.BR RNDGETENTCNT +Retrieve the entropy count of the input pool, the contents will be the same +as the +.I entropy_avail +file under proc. +The result will be stored in the int pointed to by the argument. +.TP +.BR RNDADDTOENTCNT +Increment or decrement the entropy count of the input pool by the value pointed +to by the argument. +.TP +.BR RNDGETPOOL +Removed in Linux 2.6.9. +.TP +.BR RNDADDENTROPY +Add some additional entropy to the input pool, incrementing the entropy count. +Unlike writing to \fI/dev/random\fP or \fI/dev/urandom\fP which only adds some +data but does not increment the entropy count. The following structure is used: +.IP +.IN +4n +.NF +struct rand_pool_info { + int entropy_count; + int buf_size; + __u32 buf[0]; +}; +.FI +.IN +.IP +Here +.I entropy_count +is the value added to (or subtracted from) from the entropy count. And +.I buf +is the buffer of size +.I buf_size +which gets added to the entropy pool. +.TP +.BR RNDZAPENTCNT ", " RNDCLEARPOOL +Zero the entropy count of all pools and add some system data (such as +wall clock) to the pools. .SH FILES /dev/random .br |