Unattended, unintended system shutdown - why?

[David Fletcher]

I have a home server which until just before Christmas was running
32-bit Ubuntu Server 10.04, 24/7, for over four years, with zero
problems. Because 10.04 is almost at the end of LTS, I upgraded to
14.04, fresh install on a fresh hard drive. Until now that's been
running perfectly, 24/7, too. I went away for a one week ski break on
22nd Feb, during which I remotely updated and, because there was a new
kernel, rebooted the server. No problem.

Just establishing that I have a reliable system.

Then, today, I walked into town for couple of hours, came back, switched
on my laptop to check my mail and... nothing. Failed to connect. WTF?
ssh - nothing. ping - nothing. went upstairs to check and it was powered
off. Pressed the button and it powered up, and is working again. Why? I
have absolutely no idea. Yes it's running on a UPS so this should never,
ever happen.

Any idea why it did this, please?

syslog entries from the time this happened follow:-

Mar  7 11:42:40 ServerIII postfix/qmgr[1185]: BBD424FE0177:
from=<ebay at ebay.co.uk>, size=132672, nrcpt=1 (queue active)
Mar  7 11:42:40 ServerIII postfix/local[9879]: BBD424FE0177:
to=<Address at removed>, orig_to=<Address at removed>, relay=local, delay=1.1,
delays=1/0.02/0/0.06, dsn=2.0.0, status=sent (delivered to maildir)
Mar  7 11:42:40 ServerIII postfix/qmgr[1185]: BBD424FE0177: removed
Mar  7 11:42:40 ServerIII postfix/smtpd[9874]: disconnect from
mxslcpool07.ebay.com[66.135.215.73]
Mar  7 11:44:01 ServerIII CRON[9881]: (jf) CMD (getmail --quiet
--rcfile=/home/jf/.getmail4rc-hotmail)
Mar  7 11:46:01 ServerIII postfix/anvil[9876]: statistics: max
connection rate 1/60s for (smtp:66.135.215.73) at Mar  7 11:42:38
Mar  7 11:46:01 ServerIII postfix/anvil[9876]: statistics: max
connection count 1 for (smtp:66.135.215.73) at Mar  7 11:42:38
Mar  7 11:46:01 ServerIII postfix/anvil[9876]: statistics: max cache
size 1 at Mar  7 11:42:38
Mar  7 11:49:01 ServerIII CRON[9886]: (dave) CMD (getmail --quiet
--rcfile=/home/dave/.getmail4rc-yahoo)
Mar  7 11:54:01 ServerIII CRON[9889]: (jf) CMD (getmail --quiet
--rcfile=/home/jf/.getmail4rc-hotmail)
Mar  7 11:55:59 ServerIII dovecot: imap-login: Login: user=<jf>,
method=PLAIN, rip=86.26.201.179, lip=192.168.2.2, mpid=9897, TLS,
session=<6tj8e7EQhwBWGsmz>
Mar  7 11:55:59 ServerIII dovecot: imap-login: Login: user=<jf>,
method=PLAIN, rip=86.26.201.179, lip=192.168.2.2, mpid=9898, TLS,
session=<t978e7EQmwBWGsmz>
Mar  7 11:55:59 ServerIII dovecot: imap(jf): Connection closed in=54
out=951
Mar  7 11:56:28 ServerIII dovecot: imap(jf): Connection closed in=23
out=1042
Mar  7 11:59:01 ServerIII CRON[9900]: (dave) CMD (getmail --quiet
--rcfile=/home/dave/.getmail4rc-yahoo)
Mar  7 12:01:05 ServerIII dbus[327]: [system] Activating service
name='org.freedesktop.systemd1' (using servicehelper)
Mar  7 12:01:05 ServerIII dbus[327]: [system] Successfully activated
service 'org.freedesktop.systemd1'
Mar  7 06:39:59 ServerIII rsyslogd: [origin software="rsyslogd"
swVersion="7.4.4" x-pid="402" x-info="http://www.rsyslog.com"] rsyslogd
was HUPed
Mar  7 12:01:05 ServerIII rsyslogd: [origin software="rsyslogd"
swVersion="7.4.4" x-pid="402" x-info="http://www.rsyslog.com"] exiting
on signal 15.


Arrived back home, fired up the server again....


Mar  7 12:22:21 ServerIII rsyslogd: [origin software="rsyslogd"
swVersion="7.4.4" x-pid="398" x-info="http://www.rsyslog.com"] start
Mar  7 12:22:21 ServerIII rsyslogd: rsyslogd's groupid changed to 104
Mar  7 12:22:21 ServerIII rsyslogd: rsyslogd's userid changed to 101
Mar  7 12:22:21 ServerIII kernel: [    0.000000] Initializing cgroup
subsys cpuset
Mar  7 12:22:21 ServerIII kernel: [    0.000000] Initializing cgroup
subsys cpu
Mar  7 12:22:21 ServerIII kernel: [    0.000000] Initializing cgroup
subsys cpuacct
Mar  7 12:22:21 ServerIII kernel: [    0.000000] Linux version
3.13.0-46-generic (buildd at orlo) (gcc version 4.8.2 (Ubuntu
4.8.2-19ubuntu1) ) #77-Ubuntu SMP Mon Mar 2 18:26:13 UTC 2015 (Ubuntu
3.13.0-46.77-generic 3.13.11-ckt15)
Mar  7 12:22:21 ServerIII kernel: [    0.000000] KERNEL supported cpus:
Mar  7 12:22:21 ServerIII kernel: [    0.000000]   Intel GenuineIntel
Mar  7 12:22:21 ServerIII kernel: [    0.000000]   AMD AuthenticAMD
Mar  7 12:22:21 ServerIII kernel: [    0.000000]   NSC Geode by NSC
Mar  7 12:22:21 ServerIII kernel: [    0.000000]   Cyrix CyrixInstead
Mar  7 12:22:21 ServerIII kernel: [    0.000000]   Centaur CentaurHauls
Mar  7 12:22:21 ServerIII kernel: [    0.000000]   Transmeta
GenuineTMx86
Mar  7 12:22:21 ServerIII kernel: [    0.000000]   Transmeta
TransmetaCPU
Mar  7 12:22:21 ServerIII kernel: [    0.000000]   UMC UMC UMC UMC
Mar  7 12:22:21 ServerIII kernel: [    0.000000] Disabled fast string
operations
Mar  7 12:22:21 ServerIII kernel: [    0.000000] e820: BIOS-provided
physical RAM map:
Mar  7 12:22:21 ServerIII kernel: [    0.000000] BIOS-e820: [mem
0x0000000000000000-0x000000000009ebff] usable
Mar  7 12:22:21 ServerIII kernel: [    0.000000] BIOS-e820: [mem
0x000000000009ec00-0x000000000009ffff] reserved
Mar  7 12:22:21 ServerIII kernel: [    0.000000] BIOS-e820: [mem
0x00000000000e0000-0x00000000000fffff] reserved
Mar  7 12:22:21 ServerIII kernel: [    0.000000] BIOS-e820: [mem
0x0000000000100000-0x000000007f4b0fff] usable
Mar  7 12:22:21 ServerIII kernel: [    0.000000] BIOS-e820: [mem
0x000000007f4b1000-0x000000007f4dbfff] ACPI NVS
Mar  7 12:22:21 ServerIII kernel: [    0.000000] BIOS-e820: [mem
0x000000007f4dc000-0x000000007f5d6fff] reserved
Mar  7 12:22:21 ServerIII kernel: [    0.000000] BIOS-e820: [mem
0x000000007f5d7000-0x000000007f5d8fff] ACPI data