Will try to answer the ones I can:

Assuming the answer by Jokerdino was already checked: http://askubuntu.com/a/141607/7035

Nvidia / Ati issues

This happens when a driver has a problem installing correctly (Most cases). For this do the following:

1. Boot PC leaving SHIFT pressed to make the GRUB Menu show.

2. Select Recovery Mode which will continue booting correctly until the Recovery Menu appeares.

3. Select from the recovery menu failsafeX.

4. In some cases failsafeX will load fine (You lucky dog), for others (Me) it will give an error along the lines of "The system is running in low-graphics mode" and will stay there forever. When this happens, press CTRL+ALT+F1 to go to the terminal. Type in your Username and Password.

5. Reinstall the drivers depending on your case:

   NVIDIA

   sudo apt-get install nvidia-current - More stable/tested version sudo apt-get install nvidia-current-updates - More up-to-date version

   For other cases see this answer for details and follow the links there to help you along the way.

   ATI

   The simple way is to sudo apt-get install fglrx. If this does not work keep reading.

   Go to http://support.amd.com/us/gpudownload/Pages/index.aspx, download the one you need, put it in some folder (rename it to "ati.run" to simplify name). Go to the folder where you downloaded the file and type chmod +x ati.run to give it Executable Permission. Now just simply ./sh ati.run and follow the onscreen steps.

   After rebooting all problems should be solved. If you test ‘Additional Drivers‘ with a problem like this it will finish downloading the package but then it will give an error. It also gives the same error if you use ‘Software Center‘ and ‘Synaptic‘. The only way was to go to the failsafeX option and do the workaround about changing to the tty1 terminal and doing it via command line.

   I also need to add that I do not recommend downloading the Drivers from the Nvidia site since they:

   • Might create additional problems with Ubuntu
   • Are not updated automatically
   • Are not tested thoroughly in Ubuntu

   Always use the nvidia-current package or the nvidia-current-updates one. This are tested and approved already for the Ubuntu version you are using and will give less errors and incompatibility bugs.

Intel

For Intel it is recommended to do the following after doing all the steps mentioned above but before installing anything (When you are in the Terminal). You can choose from the Xorg-Edgers which is an Unstable PPA or the X-Swat which is more stable:

Warning: This PPA is very unstable for some things. So do it with that in mind.
sudo add-apt-repository ppa:xorg-edgers/ppa -y

or X-Swat:
sudo add-apt-repository ppa:ubuntu-x-swat/x-updates -y

After that sudo apt-get update and you should receive several updates. X-Swat currently does not have Intel drivers in the latest versions of Ubuntu.

UPDATE: Added this extensive answer to solve many of the problems that might end with the error mentioned here: Which driver should I install when using an Nvidia, Ati or Intel video card

Like always please test and give feedback so I can enhance my answer since others will be also reading it. The better it is, the more people it will help.

I solved this problem by reinstalling ubuntu-desktop.

When the message that "your system is running in low-graphics mode" appears, press Ctrl+Alt+F1, then login with your credentials.

And then, run the following commands:

• sudo apt-get install --reinstall ubuntu-desktop
• sudo reboot

The greeter is invalid

This is a bug in LightDM and a bug report has already been filed.

The reason why you end up with this failsafe X is because the pantheon-greeter you installed along with the elementary desktop is now not available and LightDM is not able to identify an alternative greeter.

As a workaround, you can edit the LightDM conf file and correct the error.

Run the following command in a terminal:

sudo nano /etc/lightdm/lightdm.conf

and change the line

greeter-session=pantheon-greeter

to

greeter-session=unity-greeter

and save it.

After changing the file, reboot and you will now be greeted with Unity greeter.

When this happens there is often an error message indicating why it failed to start X.

Look in your /var/log/Xorg.0.log.old or /var/log/Xorg.0.log. The error (if there is one) will be at the tail end of the file. Another good place to look is the log files in /var/log/gdm/* (or /var/log/lightdm/* in oneiric).

Did you happen to manually install fglrx prior to noticing the problem? If it was not uninstalled properly it can cause weird random issues. Directions for purging fglrx are available at here.

Is your video card an AGP model? If so, a common issue with ati agp cards is having an incorrect AGPMode. Sometimes you can adjust this setting in your BIOS (which perhaps windows screwed with?) There is also a setting in /etc/X11/xorg.conf for adjusting it in X.

You have too many files on your computer, and have exhausted disk space

Try moving personal files off the computer onto a USB drive.

To check whether this is the issue:

1. Press Ctrl + Alt + F1
2. Type df -h
3. If you see that there is no space available on the root (/) then you need to free some space.

To free space you can:

1. sudo apt-get autoclean
2. Look for large directories with sudo du -sc /*/* |sort -g and delete unwanted content,

3. Clean your home directory using a combination of

   cd ~   
   du -sc * |sort -g
   rm myLargeFile
   

When this is done, restart: shutdown -r now

Only for ATI graphics cards

When the message that "your system is running in low-graphics mode" appears:
Press Ctrl+Alt+F1 to see the terminal one. Then login with your credentials, and then run the following commands:

sudo apt-get install fglrx    
sudo reboot

The same can be done from the recovery mode (after enabling networking), if your Ubuntu completly refuses to enter anything but recovery mode.

Let‘s assume, arrogantly, that it is a problem with your X display manager.

Enter the terminal (you can use a virtual console if you cannot use a graphical terminal window), the one you said that you have access to, and enter the following:

sudo apt-get install gdm

. . . and choose gdm.

Then type:

sudo service gdm restart

(Or ... start instead of restart.)

According to https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1070150 this is a way to workaround a bug with lightdm.

Before typing that, you may need to first stop the other display manager that is running. This is usually LightDM:

sudo service lightdm stop

If you have trouble getting GDM to start, and this is an installed system rather than a live environment, then you can just reboot and it will start automatically because you configured it as the default display manager. (You should be able to shut down and restart normally. Otherwise, one way to reboot if the GUI is not working properly is to press Ctrl+Alt+Delete while on a virtual console.)

• If you have a problem with the restricted (closed source) driver , then try to remove it.

Open a terminal and give this command

gksudo software-properties-gtk 

Goto Additional drivers and remove the dirver. You have to mark the Using X.Org X server -- Nouveau.

Then Reboot.

• If you have not access at all to the Desktop Environment then use the Recovery Mode.

To remove the Nvidia current driver in Ubuntu 12.10

Select the Network and your root partition will mounted as Read-Write.

Select the Root 

And then give these commands with order

apt-get remove --purge nvidia-current 
rm /etc/X11/xorg.conf 
apt-get install ubuntu-desktop
reboot

The last command will reboot your system and hopefully you will login normally in next reboot with the Open Source nouveau driver.

• If you have problem with the open source driver (nouveau) , in the same manner (from recovery mode) try to install the restricted (Nvidia) driver with these commands

When you reach the Root selection and after select root

To install nvidia-current driver.

 apt-get install linux-source 
 apt-get install linux-headers-$(uname -r)
 apt-get install nvidia-current 
 nvidia-xconfig 
 reboot

According to this answer : Ubuntu 12.10 Desktop does not show when I installed nvidia drivers! may need to install or reinstall the linux-headers to get the restricted Nvidia drivers work properly.

Follow these commands:

sudo apt-get update
sudo apt-get -d install --reinstall gdm
sudo apt-get remove --purge gdm

(I ran this command above, but was told by the system to use # sudo apt-get autoremove instead, after the #sudo apt-get remove --purge gdm command.)

sudo apt-get install gdm

select GDM when prompted

sudo reboot

That fixed it for me :)

It took very long to start after the reboot, 10+ mins. But I got in eventually.

I have recently received a similar issue with myPangolin Performance laptop. The folks at System 76 told me to do the following:

Click Okay and then select the option to get a terminal. (alternatively you can press ctr+alt+f1 to bring up another tty)

sudo chown lightdm:lightdm -R /var/lib/lightdm
sudo chown avahi-autoipd:avahi-autoipd -R /var/lib/avahi-autoipd
sudo chown colord:colord -R /var/lib/colord

reboot

These commands did the trick for me.

This problem destroyed my morning. It turns out that if your root filesystem runs out of space then Ubuntu will boot into low graphics mode and it‘s hard to figure out why since the xorg log shows nothing wrong. To find out from the command line if you‘re low on space type

df -h

Sample output from my machine:

Filesystem      Size  Used Avail Use% Mounted on
/dev/sda6        18G   10G  6.6G  61% /
udev            3.9G  4.0K  3.9G   1% /dev
tmpfs           3.9G  108K  3.9G   1% /tmp
tmpfs           1.6G  1.2M  1.6G   1% /run
none            5.0M     0  5.0M   0% /run/lock
none            3.9G  1.3M  3.9G   1% /run/shm
none            100M   16K  100M   1% /run/user
/dev/sda4       317G   33G  285G  11% /media/data
/dev/sda1       197M   16M  182M   8% /boot/efi

If your / mount has a high Use% (90%+) then this could be your problem. In my case,~/.xsession.errors had grown to fill most of my partition and caused me to fall into low-graphics mode. Found my answer for that in this Ubuntuforums thread:

rm ~/.xsession-errors
mkdir ~/.xsession-errors

Well, I had the same problem and solved it.

1. Start ubuntu with recovery mode from grub then choose filesystem check followed by enable networking.

2. Choose root option to get to terminal. Now uninstall the old drivers

   sh /usr/share/ati/fglrx-uninstall

3. Then reinstall the drivers following the methods for precise from this websitehttps://help.ubuntu.com/community/BinaryDriverHowto/ATI.

4. After that everything works out just fine, I suggest you do

   apt-get update && apt-get upgrade && apt-get autoremove

   -everytime you complete a step. Good luck.

I had the same problem with an Acer Aspire 3810tg. I solved it by doing the following:

• Do a normal boot
• Press Ctrl-Alt-F1 on the "Your system is running in low-graphics mode" screen
• Download the correct driver from http://support.amd.com/us/gpudownload/Pages/index.aspx, in my case (ATI Mobility Radeon HD 4330): wget http://www2.ati.com/drivers/linux/amd-driver-installer-12-4-x86.x86_64.run which should also cover your case (Mobility Radeon HD 4xxx Series)
• chmod 755 amd-driver-installer-12-4-x86.x86_64.run to make the file executable
• sudo ./amd-driver-installer-12-4-x86.x86_64.run and follow the standard steps
• You might need to run: sudo aticonfig --initial, but that was not necessary for me.

In my case the driver installation finished with an error, but it still worked. I hope this helps.

It is not related to nvidia drivers. Because by default Ubuntu uses non-nvidia drivers even though you might have nvidia GPUs. I have an nvidia GPU too.

My Ubuntu used to boot fine until something happened which caused the same issue. After reading posts, reading logs and little bit trial and error, turns out the problem is related to lightdm GUI server.

I dont know solution to the problem but there is a quick work around in 3 steps. This will save you from reinstalling Ubuntu.

Step1: When the error shows up, hit Ctrl+Alt+F1. This will open the commandline interface. Login as root.

Step2: Remove a particular X11 config file. This file is not really required.

rm /etc/X11/xorg.conf.failsafe

Somehow the existence of the above X11 configuration file causes the OS to throw that error.

Step3: Restart lightdm GUI server.

service lightdm restart

This will restart the lightdm GUI server and voila your desktop is back!

Try delete your /etc/X11/xorg.conf and restart.

Before restart, run

sudo apt-get install xserver-xorg-video-ati xserver-xorg-video-radeon

I had a similar problem.

When I was booting my PC, i was getting the following message: “Ubuntu is running in low-graphics mode”

When I used startx on the command prompt however, everything was fine and i could start the xserver.

Now I found out that for some strange reason GDM has been uninstalled (it took me hours to realize that), i did fix the problem by reinstalling gdm with:

apt-get install gdm

now everything‘s running. Hope this helps you.

Install gdm.

During the installation of gdm you will be asked to select either gdm or lightdm as the default login display manager. Select gdm.

By the way, the fact that you have this problem on 2 different computers is a sign that there may be an irregular voltage to your computer power supply. To test for this possibility take one computer to a different address and try booting it there.

Wich ubuntu version are you running? Did you installed graphics drivers before the problem or is it a post clean-os-install issue? Giving some more info would be helpful for us to help you.

If you messed with the graphic drivers before the problem came up, get to the login screen, press Ctrl+Alt+F1, login, then:

• sudo apt-get purge nvidia-*
• sudo apt-get autoremove
• sudo apt-get linux-source linux-headers-generic
• sudo apt-get install nvidia-current
• sudo nvidia-xconfig
• sudo shutdown -r now

Of course, if you have an ATI videocard you have to change the nvidia-* and nvidia-current for your ATI drivers package.

Try to boot from grub using a different parameter or even booting an older kernel from the list.

https://help.ubuntu.com/community/BootOptions

See the section on kernel options. Something like: xforcevesa

Good luck! :)

Follow these commands:

sudo apt-get update
sudo apt-get -d install --reinstall gdm
sudo apt-get remove --purge gdm
sudo apt-get install gdm
sudo apt-get remove --purge xserver-xgl compiz compiz-plugins compiz-core compiz-manager csm cgwd cgwd-themes
sudo apt-get install --reinstall compiz compiz-core compiz-fusion-plugins-extra compiz-fusion-plugins-main compiz-gnome compiz-plugins libcompizconfig0
sudo dpkg-reconfigure -phigh xserver-xorg

choose the driver ‘ati‘ and when you get to monitor resolution choose the resolution you want to run and any resolution ABOVE that resolution should be removed. Once that is done issue the following:*

sudo reboot

You will most likely get errors on specific packages. Repeat the command removing the problem package until it works.

There will be a time where you will be without the desktop, so have another internet connected device nearby to reference this from or to Google with in case of emergency.

This worked for me, hope this helps.

*If you are never prompted, just skip this.

I had a special case of this problem, where I somehow caused the removal of some packages. I only noticed the actual problem after some time spent looking at the problem.

So:

1. Log into the text mode console
2. Enter the command: sudo apt-get install ubuntu-desktop

This will ensure all the needed packages are installed. Without some of those, symptoms like those described here may occur.

You said that you were stuck in low graphics mode and now you say that you can only get a command prompt. What happens when you type: startx

If you are stuck in a command prompt all is not lost. You can still reconfigure xserver with: sudo dpkg --reconfigure --phigh xserver-xorg

I had the issue when I upgraded from 11.10 on my Acer Aspire One AO-722. I also had the propriety ATi/AMD driver installed from 11.10, which carried over to the 12.04 installation. I followed this guide to remove the proprietary drivers and use the Open Source drivers.http://wiki.cchtml.com/index.php/Ubuntu_Oneiric_Installation_Guide#Removing_Catalyst.2FfglrxEverything seems to be working now.

You need to install the kernel headers manually then reinstall nvidia for some reason then the nvidia drivers will work

Your Memory may be bad.

If you experience Low graphics mode intermittently like I was.

1. Run a memory check to check for memory errors.

2. Buy New memory(Make sure it is the right type for your computer)

3. Run the memory test again, to make sure all is good.

The Low Graphics Mode error should now be gone.

1. Press CTRL+ALT+F1 to open a terminal
2. log in
3. look at the end of your /var/log/Xorg.0.log

4. if the message error is Cannot run in framebuffer mode. Please specify busIDs. then run the following commands:

   sudo apt-get install --reinstall lightdm
   sudo reboot

I‘m running Ubuntu 12.04 on a Toshiba Portege R100. I got this error after the first bootup after install. After downloading and updating the graphics driver (Trident Cyberblade), what worked for me was creating a driver-specific .conf file as described in this Arch-Linux wiki:https://wiki.archlinux.org/index.php/Trident.

Phenomenon: I first saw Booting without full network configuration message that never ended. After Action-1 below, I faced The system is running in low-graphics mode issue.

Action-1: Force to shutdown the machine (by keeping power button pressed as normal). Choose recovery boot.

Effective solution: Remove & install xserver-xorg, inspired by this thread.

Edit) after creating xorg.conf and had it read in xserver, I faced the same issue again. This time, in addition to re-install xserver-xorg, I had to create /etc/X11/xorg.conf file (I did so by copying the backup file I already made).

I fixed this problem by creating a new xorg.conf file (copying the text from xorg.conf.failsafe).

Details: http://askubuntu.com/a/296217/55223

Go to System, Administration and click on Hardware drivers (in Maverick it is called Additional Drivers). It will search for and allow you to install the proper graphics driver which should allow you to run in higher res.

In Linux there are two ways to do most things, by the GUI or by the terminal. This is easier for most people used to a graphical user interface. The second GUI way to do it would be to go to Software Center or Synaptic and install the packages in the previous post. Search for them in the search bar. I don‘t think that Ubuntu has used xorg.conf for awhile, so it would not help to look for it.