save-entropy: Add manual page

Succinct manual page for save-entropy(8).

PR:			223998
Reported by:		AJ Jordan <alex+freebsd@strugee.net>
Reviewed by:		carlavilla@, delphij@, lwhsu@, pauamma_gundo.com
Approved by:		delphi, lwhsu (src)
Differential Revision:	https://reviews.freebsd.org/D41768

(cherry picked from commit 8dc9b10e388da19d63b3dd718a8243e8e969091d)

2 files changed, 98 insertions, 0 deletions

diff --git a/libexec/save-entropy/Makefile b/libexec/save-entropy/Makefile
index 1c7eabf36c7f..0c541606411f 100644
--- a/libexec/save-entropy/Makefile
+++ b/libexec/save-entropy/Makefile
@@ -1,4 +1,5 @@
 
 SCRIPTS=	save-entropy.sh
+MAN=		save-entropy.8
 
 .include <bsd.prog.mk>
diff --git a/libexec/save-entropy/save-entropy.8 b/libexec/save-entropy/save-entropy.8
new file mode 100644
index 000000000000..f7a93c8866fc
--- /dev/null
+++ b/libexec/save-entropy/save-entropy.8
@@ -0,0 +1,97 @@
+.\"
+.\" SPDX-License-Identifier: BSD-2-Clause
+.\"
+.\" Copyright (c) 2023 Fernando Apesteguia <fernando.apesteguia@gmail.com>
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+.\" SUCH DAMAGE.
+.\"
+.Dd September 18, 2023
+.Dt SAVE-ENTROPY 8
+.Os
+.Sh NAME
+.Nm save-entropy
+.Nd Save bits of entropy to feed /dev/random at startup
+.Sh SYNOPSIS
+.Nm save-entropy
+.Sh DESCRIPTION
+The
+.Nm
+command is used to save entropy data from
+.Pa /dev/random
+to files in a specified output location.
+The files saved are used at startup to provide additional entropy for
+.Pa /dev/random .
+The output file will be different in every invocation until the maximum number
+of different files is reached.
+(See
+.Em entropy_save_num
+for details).
+By default this script is invoked via
+.Xr cron 8
+every eleven minutes approximately.
+.Pp
+This command does nothing if executed inside a
+.Xr jail 8 .
+.Pp
+Three variables in
+.Pa /etc/rc.conf
+regulate the behavior of the script:
+.Bl -tag -width Ds
+.It Va entropy_dir
+Specify the directory for saved entropy files.
+Defaults to
+.Pa /var/db/entropy .
+If set to "NO" it disables caching entropy via
+.Xr cron 8 .
+This setting is shared with
+.Pa /etc/rc.d/random .
+.It Va entropy_save_sz
+Size of the entropy cache files.
+Defaults to 4096.
+.It Va entropy_save_num
+Number of entropy cache files to save.
+Defaults to 8.
+.El
+.Sh FILES
+.Bl -tag -width Ds
+.It Pa /etc/rc.conf
+.El
+.Sh EXIT STATUS
+.Ex -std
+Errors will be recorded in the system log.
+.Sh SEE ALSO
+.Xr syslog 3 ,
+.Xr random 4 ,
+.Xr rc.conf 5 ,
+.Xr cron 8
+.Sh HISTORY
+The
+.Nm
+command first appeared in
+.Fx 5.0 .
+.Sh AUTHORS
+The
+.Nm
+command was originally written by
+.An Doug Barton <dougb@FreeBSD.org> .
+This manual page was written by
+.An Fernando Apesteguia <fernape@FreeBSD.org> .