我的 Ubuntu 机器（带有 XFCE 桌面）应该始终处于打开状态，因为我将其用作备份服务器。这是一台旧的 HP 台式机。周末我无法通过 SSH（OpenSSH）访问它。当我今天（星期一）有机会访问它时，它已关闭。我想知道它为什么会关闭，并希望得到一些帮助。请告诉我我是否应该添加更多信息。系统日志显示它运行的最后一天的内容如下：
Jul 23 03:21:44 int160 NetworkManager[711]: <info> [1469236904.0406] dhcp4 (enp63s0): state changed bound -> bound
Jul 23 03:21:44 int160 dbus[664]: [system] Activating via systemd: service name='org.freedesktop.nm_dispatcher' unit='dbus-org.freedesktop.nm-dispatcher.service'
Jul 23 03:21:44 int160 dhclient[821]: bound to 130.237.205.245 -- renewal in 17465 seconds.
Jul 23 03:21:44 int160 systemd[1]: Starting Network Manager Script Dispatcher Service...
Jul 23 03:21:44 int160 dbus[664]: [system] Successfully activated service 'org.freedesktop.nm_dispatcher'
Jul 23 03:21:44 int160 nm-dispatcher: req:1 'dhcp4-change' [enp63s0]: new request (1 scripts)
Jul 23 03:21:44 int160 nm-dispatcher: req:1 'dhcp4-change' [enp63s0]: start running ordered scripts...
Jul 23 03:21:44 int160 systemd[1]: Started Network Manager Script Dispatcher Service.
Jul 23 03:25:01 int160 CRON[9873]: (root) CMD (command -v debian-sa1 > /dev/null && debian-sa1 1 1)
Jul 23 03:35:01 int160 CRON[9999]: (root) CMD (command -v debian-sa1 > /dev/null && debian-sa1 1 1)
Jul 23 03:45:01 int160 CRON[10137]: (root) CMD (command -v debian-sa1 > /dev/null && debian-sa1 1 1)
Jul 23 03:55:01 int160 CRON[10252]: (root) CMD (command -v debian-sa1 > /dev/null && debian-sa1 1 1)
Jul 23 04:05:01 int160 CRON[10350]: (root) CMD (command -v debian-sa1 > /dev/null && debian-sa1 1 1)
Jul 23 04:15:01 int160 CRON[10434]: (root) CMD (command -v debian-sa1 > /dev/null && debian-sa1 1 1)
Jul 23 04:17:01 int160 CRON[10463]: (root) CMD ( cd / && run-parts --report /etc/cron.hourly)
Jul 23 04:25:01 int160 CRON[10545]: (root) CMD (command -v debian-sa1 > /dev/null && debian-sa1 1 1)
Jul 23 04:35:01 int160 CRON[10604]: (root) CMD (command -v debian-sa1 > /dev/null && debian-sa1 1 1)
Jul 23 04:45:01 int160 CRON[10661]: (root) CMD (command -v debian-sa1 > /dev/null && debian-sa1 1 1)
Jul 23 04:49:03 int160 systemd[1]: Starting Automatically refresh installed snaps...
Jul 23 04:49:03 int160 /usr/lib/snapd/snapd[704]: daemon.go:181: DEBUG: uid=0;@ GET /v2/find?q=&select=refresh 259.215029ms 200
Jul 23 04:49:03 int160 /usr/lib/snapd/snapd[704]: daemon.go:181: DEBUG: uid=0;@ GET /v2/snaps 81.209µs 200
Jul 23 04:49:03 int160 snap[10684]: No snaps are installed yet. Try 'snap install hello-world'.
Jul 23 04:49:03 int160 systemd[1]: Started Automatically refresh installed snaps.
Jul 23 04:49:03 int160 systemd[1]: snapd.refresh.timer: Adding 2h 15min 16.921260s random time.
Jul 23 04:49:03 int160 systemd[1]: snapd.refresh.timer: Adding 3h 58min 57.466385s random time.
Jul 23 04:55:01 int160 CRON[10723]: (root) CMD (command -v debian-sa1 > /dev/null && debian-sa1 1 1)