Ubuntu 12.04 sleeps spontaneously, where to dig?

Question

linux

Sometimes (the last time was a month or two ago) my Ubuntu spontaneously goes into Sleep Mode. I can’t understand what’s the matter - I’m working, everything is OK, and then the screen goes blank and sleep mode on. I thought maybe I accidentally pressed a key - no, I just clicked the mouse in the browser and again.
Where to look, what to dig? There is something strange in the logs:
Nov 12 15:40:01 oleg CRON[24827]: (smmsp) CMD (test -x /etc/init.d/sendmail && /usr/share/sendmail/sendmail cron-msp)
Nov 12 15:40:01 oleg sm-msp-queue[24842]: My unqualified host name (oleg) unknown; sleeping for retry
Nov 12 15:40:31 oleg NetworkManager[1313]: <info> sleep requested (sleeping: no enabled: yes)
Nov 12 15:40:31 oleg NetworkManager[1313]: <info> sleeping or disabling.. .
Nov 12 15:40:31 oleg NetworkManager[1313]: <info> (eth1): now unmanaged
Nov 12 15:40:31 oleg NetworkManager[1313]: <info> (eth1): device state change: activated -> unmanaged (reason 'sleeping') [100 10 37]
Nov 12 15:40:31 oleg NetworkManager[1313]: <info> (eth1): deactivating device (reason 'sleeping') [37]
Nov 12 15:40:31 oleg NetworkManager[1313]: <info> (eth1): canceled DHCP transaction, DHCP client pid 18939
Nov 12 15:40:31 oleg NetworkManager[1313]: <info> (eth1): removing resolv.conf from /sbin/resolvconf
Nov 12 15:40:31 oleg NetworkManager[1313]: <info> (eth1): cleaning up...
Nov 12 15:40:31 oleg NetworkManager[1313]: <info> (eth1): taking down device.
Nov 12 15:40:31 oleg NetworkManager[1313]:
Nov 12 15:40:31 oleg NetworkManager[1313]: <info> (eth0): device state change: unavailable -> unmanaged (reason 'sleeping') [20 10 37]
Nov 12 15:40:31 oleg NetworkManager[1313 ]: <info> (eth0): cleaning up...
Nov 12 15:40:31 oleg dbus[1280]: [system] Activating service name='org.freedesktop.nm_dispatcher' (using servicehelper)
Nov 12 15:40 :31 oleg NetworkManager[1313]: <info> (eth0): taking down device.
Nov 12 15:40:31 oleg dbus[1280]: [system] Successfully activated service 'org.freedesktop.nm_dispatcher'
Nov 12 15:40:31 oleg NetworkManager[1313]: <info> (eth2): now unmanaged
Nov 12 15:40:31 oleg NetworkManager[1313]: <info> (eth2): device state change: unavailable -> unmanaged (reason 'sleeping'
Nov 12 15:40:31 oleg NetworkManager[1313]: <info> (eth2): cleaning up...
Nov 12 15:40:31 oleg NetworkManager[1313]: <info> (eth2): taking down device.
Nov 12 15:40:31 oleg NetworkManager[1313]: <info> (eth1): carrier now OFF (device state 10)
Nov 12 15:40:32 oleg anacron[24966]: Anacron 2.3 started on 2012-11-12
Nov 12 15:40:32 oleg anacron[24966]: Normal exit (0 jobs run)
Nov 12 15:40:48 oleg kernel: [349982.860120] PM: Syncing filesystems ... done.
Nov 12 15:40:48 oleg kernel: [349983.160306] PM: Preparing system for mem sleep
Nov 12 15:40:48 oleg kernel: [349983.160312] Freezing user space processes ... (elapsed 0.01 seconds) done.
Nov 12 15:40:48 oleg kernel: [349983.174605] Freezing remaining freezable tasks ... (elapsed 0.01 seconds) done.
Nov 12 15:40:48 oleg kernel: [349983.190599] PM: Entering mem sleep

Answer 1

www.mossyadmin.ru/2010/02/my-unqualified-host-name-hostname.html