ubuntu won't shutdown or freezes at splash screen

Try pressing escape when it is frozen to see the shutdown commands behind the splash screen. Or remove "quiet splash" from this line in etc/default/grub GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"

you can do this by editing the etc/default/grub file

sudo gedit etc/default/grub - make the edit so it looks like this GRUB_CMDLINE_LINUX_DEFAULT=""

If you had other parameters between the "" you can leave them in the line then update grub with

sudo update-grub

On start up and shut down you should see the boot sequences commands now. If you see Reached target shutdown and that is where it hangs forever this may be related to bug #1464917:

If you feel this is related to this bug please go to the link above and add your name to the "This affects me " link at the top of the bug description

Update:

There has been a development as a work around to this bug. It seems to be related to the swap file usage/management. Adam (from the bug link above) points out that if you turn your swap off, wait for it to process, before you shutdown the hang never happens. When you are ready to shutdown your machine, open a terminal window and type;

sudo swapoff -a

Wait for the command to process and give your prompt back then you should be able to perform normal shutdown. This is working for many including me.

end update

After the shutdown or reboot has hanged with this message Reached target Shutdown

Try Sysrq

Hold down the Alt and SysRq (Print Screen) keys.
While holding those down, type the following keys in order, several seconds apart: REISUB
Computer should reboot.

You can also try the following after it hangs.

see if you can login tty1 and reboot

Press Ctrl+Alt+F1 or Ctrl+Alt+F2 or Ctrl+Alt+F3 ...
Write your username (lowercase, the name of the user folder in /home) and hit Enter
Write your password (nothing will appear) and hit Enter

If your password and username are correct, you are now logged in.

If that fails try Ctrl+Alt+Del a couple times at that point in the tty1 screen

You might see a message that states the machine is going to reboot and then it should do just that after a minute or so.

Its better than a hard boot - until its fixed

In the bug notes it is reported that you can upgrade to Vivid-Proposed and it fixes the issue but some still see this after that upgrade. It might be worth a shot.

Btw the same bug affects me.

I also faced startup and shutdown hanging with my Dell Inspiron 640m and Ubuntu 14.04. Different people may have different reasons of this problem but thought to share one approach what I did.

Startup was clueless, but Shutdown shows that it could not kill all the process and so mount / failed, and was busy. System hung.

So First changed the grub and removed quite splash from GRUB_CMDLINE_LINUX_DEFAULT. At least it booted this time. But it didn't solve the shutdown problem

Next, As stopping the processes was problem during shutdown, tried finding if any process got uninterruptible sleep. ie "D" in top.

$ top -bn1 | awk 'NR > 7 && $8 ~ /D/ { print $0 }'

It showed modprobe and its parent pci_devices were hung. modprobe hung with parameter --ignore-install b44. I tried loading Broadcom b43 wireless driver which hanged too. dmesgs/kern.log has shown b43 related errors.

- Dec 20 00:28:40 Chandra kernel: [   10.080226] wl: module license 'MIXED/Proprietary' taints kernel.
- Dec 20 00:28:40 Chandra kernel: [   10.080233] Disabling lock debugging due to kernel taint
- Dec 20 00:28:40 Chandra kernel: [   10.090618] wl: module verification failed: signature and/or  required key missing - tainting kernel
- Dec 20 00:28:40 Chandra kernel: [   10.702357] b43-phy0: Broadcom 4311 WLAN found (core revision 10)
- Dec 20 00:28:40 Chandra kernel: [   10.736180] b43-phy0: Found PHY: Analog 4, Type 2 (G), Revision 8
- Dec 20 00:28:40 Chandra kernel: [   10.736200] b43-phy0: Found Radio: Manuf 0x17F, ID 0x2050, Revision 2, Version 0
- Dec 20 00:28:40 Chandra kernel: [   10.748421] Broadcom 43xx driver loaded [ Features: PNL ]
- Dec 20 00:28:40 Chandra kernel: [   10.951143] b43 ssb0:0: Direct firmware load for b43/ucode5.fw failed with error -2

I didn't try blacklisting b43, b44, wl or related modules to confirm that if the problem was solved (you may try), but upgraded linux-firmware and rebooted. Amazingly, no modprobe hanging at all during startup and modprobe add/remove b44/b43 showed no problem, though wifi didn't work. Shutdown was fine too. So added the quite splash back in grub back and things were on its feet.
At last, solving wifi was easy as mentioned in some other thread to purge bcmwl-kernel-source and install firmware-b43-installer, and reboot.