On a laptop with Ubuntu 20.04 without battery after having a power outage I had the following error when booting:

blk_update_request: I/O error, dev sda, secto 1871712792 op 0x0: (READ) flags 0x0 phys_seg 1 prio class 0
Buffer I/O error on dev sda5, logical block 233832515, async page read
ata1: EH complete
Error reading block 233832515 (Input/output error) while getting next inode from scan.

        (i.e., without -a or -p options)
fsck exited with status code 4
Failure: File system check of the root filesystem failed
The root filesystem on /dev/sda5 requires a manual fsck

BusyBox v1.30.1 (Ubuntu 1:1.30.1-4ubuntu6.3) built-in shell (ash)
Enter 'help' for a list of built-in commands.

I executed the following command and accepted all its 'y' which had as default in each message:

fsck /dev/sda5

And when he finished he gave the message:

I tried to restart with 'init 6' and with 'shutdown -r now' but the commands were not available. I restarted the computer by turning off the laptop button and fixed the problem booted without Ubuntu 20.04 problems.