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/dev/sda1 is the name of the Linux device corresponding to your EFI system partition, and
/boot/efi is the location where the EFI partition is expected to be mounted.
The ACPI error messages are probably not fatal and most likely unrelated. The Linux kernel is successfully starting, but something is going wrong in the boot process. And since you have destroyed & recreated some partitions, the most likely reason is that the contents of the
/etc/fstab file no longer match the actual partitioning of your disk.
To do anything in this state, you'll first need to enter the root password. If you haven't set a specific root password, it might be the same as the password of the first user account created when installing the system. There will be no asterisks or any visible confirmation of your keystrokes until you press Enter. If you can successfully enter the root password, you will be in the command prompt with root privileges and can start checking and fixing things.
/etc/fstab file specifies the disk devices that should be automatically mounted as part of the boot procedure, and the mount point locations and mount options for them. Unless explicitly specified otherwise, the system will assume all the mounts specified are absolutely necessary and will stop the boot process and fall back into text-based emergency mode if even a single specified mount fails.
/etc/fstab, you can specify disk devices either by device name, like
/dev/sda1, or by filesystem UUID, like
UUID=<some hexadecimal numbers>. The UUID is a number generated at the time the filesystem is created ("formatted"), and is essentially random. By default, modern Ubuntu uses the latter method to specify that the EFI system partition needs to be mounted to
/boot/efi. The resulting line in
/etc/fstab should look somewhat like this:
UUID="XXXX-XXXX" /boot/efi vfat umask=0077,shortname=winnt,flush,tz=UTC,codepage=437,iocharset=iso8859-1 0 2
This allows the system to mount the correct partition even if you make changes to your hardware configuration so that the disks are no longer detected in the same order as before.
Now, since you have deleted and recreated your EFI system partition, its UUID has been changed. But the instructions you followed did not seem to include any advice for updating it. You could use the
/sbin/blkid /dev/sda1 command to find out the new UUID. The response should be something like this:
/dev/sda1: LABEL="EFISYS" UUID="1BC6-5A0E" TYPE="vfat" PARTLABEL="EFISYS" PARTUUID="4fb8aadb-9507-44b5-8cab-a052a0091e2b"
The important thing is the
UUID="1BC6-5A0E" part: it tells you the UUID you need for updating your
/etc/fstab file. (The
PARTUUID is not used in
/etc/fstab, but if you ever edit your firmware boot settings using the
efibootmgr command, be aware that the UUIDs used with it are specifically PARTUUIDs.)
Most likely, once you enter the root password and reach the emergency command prompt, you will need only a few commands.
To find out the new UUID:
To edit the
nano editor fails to save the modified file, you might need to run this command and then try and edit the file again:
mount -o remount,rw /
/etc/fstab file has been successfully edited, you just need to use the
exit command to exit the emergency command prompt and resume the boot process.