mjhjmtu

I'm trying to understand what is going on with rng-tools and systemd on a Beaglebone Black dev-board that's leading to entropy depletion in /dev/random. I have about 8 dev-boards in a similar configuration and only the Beaglebone has the problem.

The Beaglebone runs a Debian derivative and has a hardware rng. The OMAP rng sustains reads from /dev/hwrand. However, after draining /dev/random the device never recovers. For example, it takes 646 seconds to read 10 bytes from /dev/random.

When I look at systemd I don't see a service enabled for the rng:

$ systemctl list-unit-files | grep -i -E 'rng|rand'
rng-tools.service generated
systemd-random-seed.service static
urandom.service static

I try to enable it, and no error is returned:

# systemctl enable rng-tools.service
rng-tools.service is not a native service, redirecting to systemd-sysv-install.
Executing: /lib/systemd/systemd-sysv-install enable rng-tools

But the service fails to enable:

$ systemctl list-unit-files | grep -i -E 'rng|rand'
rng-tools.service generated
systemd-random-seed.service static
urandom.service static

And:

$ systemctl status rng-tools
● rng-tools.service
 Loaded: loaded (/etc/init.d/rng-tools; generated; vendor preset: enabled)
 Active: failed (Result: exit-code) since Sun 2018-10-14 02:36:05 EDT; 17h ago
 Docs: man:systemd-sysv-generator(8)

There is a script in rng-tools called /etc/init.d/rng-tools that looks like a service file, but it is not a systemd service file. I don't see where it is enabled or where it feeds /dev/random. Debian may have a related bug report at Issue 776597, rng-tools: No systemd .service file. I don't believe the 776597 script is the same script shown below.

How do I fix this issue or troubleshoot it further?

Here are a couple of similar Q&A's. I have not been able to scrape useful information out of them. Part of the issue is the complexity systemd has introduced. I'm not quite following what is supposed to happen, and the finer points of the objects below /etc/systemd/system like multi-user.target.wants.

• Generated systemd unit does not start on boot


• Can start custom systemd service, can't enable it


• Unable to enable systemctl service

The rng-tools package:

$ apt-file list rng-tools
rng-tools: /etc/default/rng-tools
rng-tools: /etc/init.d/rng-tools
rng-tools: /etc/logcheck/ignore.d.server/rng-tools
rng-tools: /etc/logcheck/violations.ignore.d/rng-tools
rng-tools: /usr/bin/rngtest
rng-tools: /usr/sbin/rngd
rng-tools: /usr/share/doc/rng-tools/README.gz
rng-tools: /usr/share/doc/rng-tools/TODO.Debian
rng-tools: /usr/share/doc/rng-tools/changelog.Debian.gz
rng-tools: /usr/share/doc/rng-tools/changelog.gz
rng-tools: /usr/share/doc/rng-tools/copyright
rng-tools: /usr/share/lintian/overrides/rng-tools
rng-tools: /usr/share/man/man1/rngtest.1.gz
rng-tools: /usr/share/man/man8/rngd.8.gz

The script /etc/init.d/rng-tools.

$ cat /etc/init.d/rng-tools
#! /bin/sh
#
# rng-tools initscript for the rng-tools package
# Copr. 2003 by Henrique de Moraes Holschuh <hmh@debian.org>
# Copr. 2002 by Viral Shah <viral@debian.org>
#
### BEGIN INIT INFO
# Provides: rng-tools
# Required-Start: $remote_fs $syslog
# Required-Stop: $remote_fs $syslog
# Default-Start: 2 3 4 5
# Default-Stop: 0 1 6
### END INIT INFO
#
#
# $Id: rng-tools.init,v 1.6.2.10 2008-06-10 19:51:37 hmh Exp $

PATH=/sbin:/bin:/usr/sbin:/usr/bin
DAEMON=/usr/sbin/rngd
NAME=rngd
DESC="Hardware RNG entropy gatherer daemon"
PIDFILE=/var/run/rngd.pid

DEVICELIST="hwrng hw_random hwrandom intel_rng i810_rng"

HRNGDEVICE=/dev/hwrng
RNGDOPTIONS=
[ -r /etc/default/rng-tools ] && . /etc/default/rng-tools

test -f $DAEMON || exit 0

set -e

finddevice () 
 [ -c "$HRNGDEVICE" ] && return 0
 for i in $DEVICELIST ; do
 if [ -c "/dev/$i" ] ; then
 HRNGDEVICE="/dev/$i"
 return 0
 fi
 if [ -c "/dev/misc/$i" ] ; then
 HRNGDEVICE="/dev/misc/$i"
 return 0
 fi
 done

 echo "(Hardware RNG device inode not found)"
 echo "$0: Cannot find a hardware RNG device to use." >&2
 exit 1


START="--start --quiet --pidfile $PIDFILE --startas $DAEMON --name $NAME"
case "$1" in
 start)
 echo -n "Starting $DESC: "
 finddevice
 START="$START -- -r $HRNGDEVICE $RNGDOPTIONS"
 if start-stop-daemon $START >/dev/null 2>&1 ; then
 echo "$NAME."
 else
 if start-stop-daemon --test $START >/dev/null 2>&1; then
 echo "(failed)."
 exit 1
 else
 echo "$DAEMON already running."
 exit 0
 fi
 fi
 ;;
 stop)
 echo -n "Stopping $DESC: "
 if start-stop-daemon --stop --quiet --pidfile $PIDFILE 
 --startas $DAEMON --retry 10 --name $NAME 
 >/dev/null 2>&1 ; then
 echo "$NAME."
 else
 if start-stop-daemon --test $START >/dev/null 2>&1; then
 echo "(not running)."
 exit 0
 else
 echo "(failed)."
 exit 1
 fi
 fi
 ;;
 restart|force-reload)
 $0 stop
 exec $0 start
 ;;
 *)
 echo "Usage: $0 restart" 1>&2
 exit 1
 ;;
esac

exit 0

Dmesg's related to the rng:

$ dmesg | grep -i -E 'rand|rng'
[ 4.560639] random: systemd-udevd urandom read with 11 bits of entropy available
[ 11.086922] systemd[1]: Starting Load/Save Random Seed...
[ 15.022431] using random self ethernet address
[ 15.022465] using random host ethernet address
[ 15.027177] using random self ethernet address
[ 15.027195] using random host ethernet address
[ 21.308396] omap_rng 48310000.rng: OMAP Random Number Generator ver. 20
[ 34.690558] random: nonblocking pool is initialized

And systemd dump for rng-tools:

-> Unit rng-tools.service:
 Description: rng-tools.service
 Instance: n/a
 Unit Load State: loaded
 Unit Active State: failed
 State Change Timestamp: Sun 2018-10-14 02:36:05 EDT
 Inactive Exit Timestamp: Sun 2018-10-14 02:36:04 EDT
 Active Enter Timestamp: n/a
 Active Exit Timestamp: n/a
 Inactive Enter Timestamp: Sun 2018-10-14 02:36:05 EDT
 GC Check Good: yes
 Need Daemon Reload: no
 Transient: no
 Slice: system.slice
 CGroup: n/a
 CGroup realized: no
 CGroup mask: 0x0
 CGroup members mask: 0x0
 Name: rng-tools.service
 Documentation: man:systemd-sysv-generator(8)
 Fragment Path: /run/systemd/generator.late/rng-tools.service
 Source Path: /etc/init.d/rng-tools
 Condition Timestamp: Sun 2018-10-14 02:36:04 EDT
 Condition Result: yes
 Assert Timestamp: Sun 2018-10-14 02:36:04 EDT
 Assert Result: yes
 Requires: system.slice
 Requires: sysinit.target
 WantedBy: multi-user.target
 WantedBy: graphical.target
 Conflicts: shutdown.target
 Before: shutdown.target
 Before: multi-user.target
 Before: graphical.target
 After: systemd-journald.socket
 After: system.slice
 After: remote-fs.target
 After: sysinit.target
 After: systemd-journald-dev-log.socket
 After: basic.target
 References: remote-fs.target
 References: graphical.target
 References: sysinit.target
 References: system.slice
 References: multi-user.target
 References: systemd-journald.socket
 References: systemd-journald-dev-log.socket
 References: basic.target
 References: shutdown.target
 ReferencedBy: multi-user.target
 ReferencedBy: graphical.target
 StopWhenUnneeded: no
 RefuseManualStart: no
 RefuseManualStop: no
 DefaultDependencies: yes
 OnFailureJobMode: replace
 IgnoreOnIsolate: no
 Service State: failed
 Result: exit-code
 Reload Result: success
 PermissionsStartOnly: no
 RootDirectoryStartOnly: no
 RemainAfterExit: yes
 GuessMainPID: no
 Type: forking
 Restart: no
 NotifyAccess: none
 NotifyState: unknown
 KillMode: process
 KillSignal: SIGTERM
 SendSIGKILL: yes
 SendSIGHUP: no
 UMask: 0022
 WorkingDirectory: /
 RootDirectory: /
 NonBlocking: no
 PrivateTmp: no
 PrivateNetwork: no
 PrivateDevices: no
 ProtectHome: no
 ProtectSystem: no
 IgnoreSIGPIPE: no
 RuntimeDirectoryMode: 0755
 LimitNOFILE: 4096
 LimitNOFILESoft: 1024
 StandardInput: null
 StandardOutput: journal
 StandardError: inherit
 SyslogFacility: daemon
 SyslogLevel: info
 -> ExecStart:
 Command Line: /etc/init.d/rng-tools start
 -> ExecStop:
 Command Line: /etc/init.d/rng-tools stop