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random.4: Minor tweaks to Nikos Mavrogiannopoulos's patch 

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Michael Kerrisk 2016-11-10 12:38:58 +01:00
parent 67b7fcba2b
commit f64f220c5e
1 changed files with 19 additions and 14 deletions
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man4/random.4
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@ -36,23 +36,26 @@ number of bits of noise in the entropy pool.
From this entropy pool random numbers are created.
.LP
Linux 3.17 and later provides the simpler and safer (see below)
.BR getrandom(2)
.BR getrandom (2)
interface which requires no special files.
.LP
When read, the \fI/dev/urandom\fP device return random bytes using a pseudorandom
number generator seeded from the entropy pool. That operation is
non-blocking. When used during early boot time, this device may return
When read, the
.I /dev/urandom
device returns random bytes using a pseudorandom
number generator seeded from the entropy pool.
That operation is non-blocking.
When used during early boot time, this device may return
data prior to the entropy pool being initialized.
If this is of concern in your application, use
.BR getrandom(2)
.BR getrandom (2)
or \fI/dev/random\fP instead.
.LP
The \fI/dev/random\fP device is a legacy interface which dates back to
a time where the cryptographic primitives used in the implementation
of \fI/dev/urandom\fP were not widely trusted. It will return random bytes
only within the estimated number of bits of fresh noise in the entropy
pool, blocking if necessary.
of \fI/dev/urandom\fP were not widely trusted.
It will return random bytes only within the estimated number of
bits of fresh noise in the entropy pool, blocking if necessary.
\fI/dev/random\fP is suitable for applications that need very
high quality randomness, and can afford indeterminate delays.
When the entropy pool is empty, reads from \fI/dev/random\fP will block
@ -113,9 +116,10 @@ interface is considered a legacy interface, and
.IR /dev/urandom ,
is preferred and sufficient in all use cases, with the exception of
applications which require randomness during early boot time; for
these applications, the system call
.BR getrandom(2)
must be used instead, because will block until the entropy pool is initialized.
these applications,
.BR getrandom (2)
must be used instead,
because it will block until the entropy pool is initialized.
If a seed file is saved across reboots as recommended below (all major
Linux distributions have done this since 2000 at least), the output is
@ -323,9 +327,10 @@ which gets added to the entropy pool.
.BR RNDZAPENTCNT ", " RNDCLEARPOOL
Zero the entropy count of all pools and add some system data (such as
wall clock) to the pools.
.SH KNOWN ISSUES
When used during early boot, \fI/dev/urandom\fP may return data prior to the entropy pool being initialized.
.SH BUGS
When used during early boot,
.I /dev/urandom
may return data prior to the entropy pool being initialized.
.SH FILES
/dev/random
.br