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When I try to login to my system I am automatically thrown back to the login screen.I tried

ctrl+alt+f1

but I got an error named 'signature error' Please help....

I'm using Ubuntu ver 14.04

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please mention your ubuntu version –  Creator Jun 28 at 8:14

1 Answer 1

Assuming a recent Ubuntu version and trouble with signature on the kernel or initramfs...

Boot, press shift to display the grub boot menu where you should see
Advanced options for Ubuntu ... use the arrow keys and select it, then press enter.

A new menu appears, I hope you have several entries like Ubuntu, with Linux ... NOTE: the ones having a '(recovery mode)' designation are for troubleshooting and requires some basic knowledge.

Try them out one at a time... generally the second kernel variant may well work - as trouble have a tendency to be with the latest change (shown topmost ;-)

Assuming you find one that works, you may remove the troublesome with:

sudo apt-get purge linux-image-x.x.x.x-generic    # remove kernel version x.x.x.x
sudo update-initramfs -u                          # remakes boot ramdisk
sudo update-grub2                                 # re-creates boot menu

... typed at the Terminal prompt $ (Hold CTRL+ALT and hit 'T' to open a Terminal) - the portions AFTER # are comments, not required to type.

To be able to fill in 'x.x.x.x-...' above you can type

sudo apt-get purge linux-image-

... and hit the Tab key (repeat pressing it) to list "matching" items. Fill in at least one more character from the matching items and press Tab again to get more filled in.

Note that you MUST have at least ONE 'linux-image-x.x.x.x' present to be able to get into your OS... and if you leave only one, that one MUST be working unless you wish to do extensive advanced recovery.



In the case when there is just one kernel you need to run the 'Recovery' option.
This will present you a menu with several options.

The first to run is the one having "fsck" stated, it checks the file systems (partitions) you have for consistency, then remounts them in Read/Write mode. Without this you won't be able to change settings.

The thing to try after that is "root prompt", which I hope will allow you to do the "update initramfs" and "update-grub2" commands as shown above.

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All I have is the recovery and one ubuntu and linux –  darkdragon96 Jun 28 at 9:17
    
updated text above... Please tell if that helps. –  Hannu Jun 28 at 9:25
    
Recovery options - covered –  Hannu Jul 9 at 16:49

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