I've had this happen again overnight. This time there is no BUG reported in syslog; the system just 'hangs'. 

I cannot login via screen saver, connecting via ssh gives a 'No route to host' error. There is nothing in any of the logs that indicates any problem

---------------- syslog --------------------------
May 19 01:04:38 LeosLinux stunnel: LOG5[2589:140114948318976]: Connection closed: 5250 bytes sent to SSL, 27294994 bytes sent to socket
May 19 01:04:38 LeosLinux stunnel: LOG5[2589:140114948388608]: Connection closed: 5120 bytes sent to SSL, 27982780 bytes sent to socket
May 19 01:09:01 LeosLinux CRON[10962]: (root) CMD (  [ -x /usr/lib/php5/maxlifetime ] && [ -d /var/lib/php5 ] && find /var/lib/php5/ -depth -mindepth 1 -maxdepth 1 -type f -cmin +$(/usr/lib/php5/maxlifetime) -delete)
May 19 01:17:01 LeosLinux CRON[11019]: (root) CMD (   cd / && run-parts --report /etc/cron.hourly)
May 19 01:39:01 LeosLinux CRON[11074]: (root) CMD (  [ -x /usr/lib/php5/maxlifetime ] && [ -d /var/lib/php5 ] && find /var/lib/php5/ -depth -mindepth 1 -maxdepth 1 -type f -cmin +$(/usr/lib/php5/maxlifetime) -delete)
May 19 02:09:01 LeosLinux CRON[11148]: (root) CMD (  [ -x /usr/lib/php5/maxlifetime ] && [ -d /var/lib/php5 ] && find /var/lib/php5/ -depth -mindepth 1 -maxdepth 1 -type f -cmin +$(/usr/lib/php5/maxlifetime) -delete)
May 19 02:17:01 LeosLinux CRON[11172]: (root) CMD (   cd / && run-parts --report /etc/cron.hourly)
May 19 02:39:01 LeosLinux CRON[11227]: (root) CMD (  [ -x /usr/lib/php5/maxlifetime ] && [ -d /var/lib/php5 ] && find /var/lib/php5/ -depth -mindepth 1 -maxdepth 1 -type f -cmin +$(/usr/lib/php5/maxlifetime) -delete)
May 19 03:00:01 LeosLinux CRON[11281]: (amandabackup) CMD (/usr/sbin//amdump MyConfig)
May 19 03:09:02 LeosLinux CRON[11367]: (root) CMD (  [ -x /usr/lib/php5/maxlifetime ] && [ -d /var/lib/php5 ] && find /var/lib/php5/ -depth -mindepth 1 -maxdepth 1 -type f -cmin +$(/usr/lib/php5/maxlifetime) -delete)
May 19 03:17:01 LeosLinux CRON[11476]: (root) CMD (   cd / && run-parts --report /etc/cron.hourly)
May 19 03:39:02 LeosLinux CRON[11537]: (root) CMD (  [ -x /usr/lib/php5/maxlifetime ] && [ -d /var/lib/php5 ] && find /var/lib/php5/ -depth -mindepth 1 -maxdepth 1 -type f -cmin +$(/usr/lib/php5/maxlifetime) -delete)
May 19 04:09:02 LeosLinux CRON[11606]: (root) CMD (  [ -x /usr/lib/php5/maxlifetime ] && [ -d /var/lib/php5 ] && find /var/lib/php5/ -depth -mindepth 1 -maxdepth 1 -type f -cmin +$(/usr/lib/php5/maxlifetime) -delete)
May 19 04:17:02 LeosLinux CRON[11632]: (root) CMD (   cd / && run-parts --report /etc/cron.hourly)
May 19 06:43:38 LeosLinux kernel: imklog 4.2.0, log source = /proc/kmsg started.
--------------------------------------------------------
I was still using the system at 1:05

A cron job (amanda backup) was started at 03:00, but failed saying that /home/llist (my home) was not found

------------------- email from amanda ---------------------
DUMP SUMMARY:
                                       DUMPER STATS                TAPER STATS
HOSTNAME     DISK        L ORIG-GB  OUT-GB  COMP%  MMM:SS   KB/s MMM:SS      KB/s
-------------------------- ------------------------------------- ----------------
LeosLinux.zu /bin        1       0       0     --    0:00   80.5   0:00     100.0
LeosLinux.zu /boot       1       0       0     --    0:00  101.3   0:01      20.0
LeosLinux.zu /etc        1       0       0     --    0:05   82.7   0:00    4500.0
LeosLinux.zu /home/llist   MISSING ----------------------------------------------
LeosLinux.zu /usr        1       0       0     --    2:16  145.8   0:00  198300.0
LeosLinux.zu /var        1       0       0     --    0:29 4659.8   0:00 1351300.0
----------------------------------------------------------------------------------------------------

I'd appreciate if anybody could suggest what to look at or has any explanation how the system can just hang without any evidence to the cause in any of the logs