I read similar posts, but could not find an applicable answer, so here is my situation. Xubuntu sometimes boots OK, but sometimes it is stuck in a loop. Here is what I observed:
After grub default boot: XUbuntu blue screen with rotating arc segment may or may not appear, but if it appears and if the arc segment rotates continuously then boot always ends up in a loop. The loop is showing fsck results then it goes away, hard disk activity, maybe screen activity, then fsck result again. Typical loop time is around a minute or more.
I tried several remedies (pulling plug on computer, on monitor, etc.) none seems to work consistently. Boot loop appears completely random. I could not find clue in dmsg or in some logs.
Recovery boot always OK, and it boots into VGA graphics only.
I have nvidia graphics card and it uses the nouveau driver.
Any suggestions?
EDIT April 25, 2017:
While in the loop Ctr=Alt+Fn1 and command sudo /etc/init.d/lightdm stop and sudo journalctl -xe gave me, excerpted:
Apr 25 11:02:12 andrasubuntu NetworkManager[1263]: <info> [1493132532.7582] device (enp0s4): Activation: successful, device activated.
Apr 25 11:02:12 andrasubuntu whoopsie[704]: [11:02:12] The default IPv4 route is: /org/freedesktop/NetworkManager/ActiveConnection/0
Apr 25 11:02:12 andrasubuntu whoopsie[704]: [11:02:12] Not a paid data plan: /org/freedesktop/NetworkManager/ActiveConnection/0
Apr 25 11:02:12 andrasubuntu whoopsie[704]: [11:02:12] Found usable connection: /org/freedesktop/NetworkManager/ActiveConnection/0
Apr 25 11:02:12 andrasubuntu whoopsie[704]: [11:02:12] online
Apr 25 11:02:13 andrasubuntu sudo[1513]: janos : TTY=tty1 ; PWD=/home/janos ; USER=root ; COMMAND=/etc/init.d/lightdm start
Apr 25 11:02:13 andrasubuntu sudo[1513]: pam_unix(sudo:session): session opened for user root by janos(uid=0)
Apr 25 11:02:13 andrasubuntu systemd[1]: Starting Light Display Manager...
-- Subject: Unit lightdm.service has begun start-up
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
--
-- Unit lightdm.service has begun starting up.
Apr 25 11:02:13 andrasubuntu dbus[707]: [system] Activating systemd to hand-off: service name='org.freedesktop.login1' unit='dbus-org.freedesktop.login1.service'
Apr 25 11:02:25 andrasubuntu dbus[707]: [system] Failed to activate service 'org.freedesktop.systemd1': timed out
Apr 25 11:02:25 andrasubuntu systemd-logind[1462]: Failed to enable subscription: Failed to activate service 'org.freedesktop.systemd1': timed out
Apr 25 11:02:25 andrasubuntu systemd-logind[1462]: Failed to fully start up daemon: Connection timed out
Apr 25 11:02:25 andrasubuntu systemd[1]: systemd-logind.service: Main process exited, code=exited, status=1/FAILURE
Apr 25 11:02:25 andrasubuntu systemd[1]: Failed to start Login Service.
-- Subject: Unit systemd-logind.service has failed
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
--
-- Unit systemd-logind.service has failed.
--
-- The result is failed.
Apr 25 11:02:25 andrasubuntu systemd[1]: systemd-logind.service: Unit entered failed state.
Apr 25 11:02:25 andrasubuntu systemd[1]: systemd-logind.service: Failed with result 'exit-code'.
Apr 25 11:02:25 andrasubuntu systemd[1]: systemd-logind.service: Service has no hold-off time, scheduling restart.
Apr 25 11:02:25 andrasubuntu systemd[1]: Stopped Login Service.
-- Subject: Unit systemd-logind.service has finished shutting down
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
--
-- Unit systemd-logind.service has finished shutting down.
Apr 25 11:02:25 andrasubuntu systemd[1]: Starting Login Service...
-- Subject: Unit systemd-logind.service has begun start-up
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
--
-- Unit systemd-logind.service has begun starting up.
Apr 25 11:02:37 andrasubuntu dbus[707]: [system] Failed to activate service 'org.freedesktop.PolicyKit1': timed out
Apr 25 11:02:37 andrasubuntu NetworkManager[1263]: <error> [1493132557.5202] auth: could not get polkit proxy: Error calling StartServiceByName for org.freedesktop.PolicyKit1: GDBus.Error:org.freedesktop.DBus.Error.TimedOut: Failed to activate service 'org.freedesktop.PolicyKit1': timed out
Apr 25 11:02:37 andrasubuntu dbus[707]: [system] Failed to activate service 'fi.w1.wpa_supplicant1': timed out
Apr 25 11:02:37 andrasubuntu NetworkManager[1263]: <warn> [1493132557.5296] supplicant: failed to acquire wpa_supplicant proxy: Wi-Fi and 802.1x will not be available (Error calling StartServiceByName for fi.w1.wpa_supplicant1: GDBus.Error:org.freedesktop.DBus.Error.TimedOut: Failed to activate service 'fi.w1.wpa_supplicant1': timed out)
Apr 25 11:02:38 andrasubuntu dbus[707]: [system] Failed to activate service 'org.freedesktop.login1': timed out
Apr 25 11:02:38 andrasubuntu lightdm[1531]: ** (lightdm:1531): WARNING **: Failed to get list of logind seats: GDBus.Error:org.freedesktop.DBus.Error.TimedOut: Failed to activate service 'org.freedesktop.login1': timed out
Apr 25 11:02:38 andrasubuntu dbus[707]: [system] Activating systemd to hand-off: service name='org.freedesktop.Accounts' unit='accounts-daemon.service'
Apr 25 11:02:50 andrasubuntu dbus[707]: [system] Failed to activate service 'org.freedesktop.systemd1': timed out
Apr 25 11:02:50 andrasubuntu systemd-logind[1537]: Failed to enable subscription: Failed to activate service 'org.freedesktop.systemd1': timed out
Apr 25 11:02:50 andrasubuntu systemd-logind[1537]: Failed to fully start up daemon: Connection timed out
Apr 25 11:02:50 andrasubuntu systemd[1]: systemd-logind.service: Main process exited, code=exited, status=1/FAILURE
Apr 25 11:02:50 andrasubuntu systemd[1]: Failed to start Login Service.
-- Subject: Unit systemd-logind.service has failed
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
--
-- Unit systemd-logind.service has failed.
--
-- The result is failed.
The loop is clearly visible. It is also evident (to me) that the problem is not nvidia graphics card related. Hope this helps.
It's true that no socket A processors feature SSE2 support. However I don't believe that's the issue. At 10 years of age, it's almost certain that your main board has liquid filled capacitors. These have been known to fail resulting in numerous seemingly unexplainable faults. Sometimes this capacitor failure is actually visible. In fact over the years I've replaced several motherboards that have exhibited similar symptoms and inspection revealed capacitors that had swollen and in some cases cracked at the top and leaking of electrolyte (brown goo) was visible. If you examine the board and see this condition you have very few choices.
The simplest and best choice in your case is to replace the computer with a new one. CPU, RAM, storage device, and interface technology is leaps and bounds ahead of what it was when your system was designed and there are many benefits to these improvements.
If a new machine isn't in the budget, it's possible to find a used or refurbished system at a good price either online, at a local repair shop, or even from someone you know that simply has to have the cutting edge and retires theit old systems purely for performance reasons.
The last and least attractive option (if you have exceptional skills with a soldering iron) is to replace the capacitors on the main board with new caps that have the same characteristics and specifications. The capacitors are very inexpensive, but the job itself is a giant pain fraught with risk.