sdb2 was mounted so I unmounted it

ubuntu@ubuntu:~$ sudo mount /dev/sda1 /mnt/boot/efi
mount: /mnt/boot/efi: mount point does not exist.
ubuntu@ubuntu:~$ for i in /dev /dev/pts /proc /sys /run; do sudo mount -B $i /mnt$i; done
ubuntu@ubuntu:~$ sudo cp /etc/resolv.conf /mnt/etc/
cp: '/etc/resolv.conf' and '/mnt/etc/resolv.conf' are the same file
ubuntu@ubuntu:~$ sudo chroot /mnt
root@ubuntu:/# fsck.ext4 -pvf /dev/sdb2
/dev/sdb2 is mounted.
e2fsck: Cannot continue, aborting.


root@ubuntu:/# sudo umount /dev/sdb2
root@ubuntu:/# fsck.ext4 -pvf /dev/sdb2

      181135 inodes used (11.40%, out of 1589248)
          48 non-contiguous files (0.0%)
         125 non-contiguous directories (0.1%)
             # of inodes with ind/dind/tind blocks: 0/0/0
             Extent depth histogram: 156648/9
     1674437 blocks used (26.36%, out of 6351104)
           0 bad blocks
           1 large file

      129833 regular files
       24540 directories
           7 character device files
           0 block device files
           0 fifos
           0 links
       26746 symbolic links (24463 fast symbolic links)
           0 sockets
------------
      181126 files
root@ubuntu:/# apt install --reinstall grub-efi-amd64 linux-generic linux-headers-generic
Reading package lists... Error!
W: Not using locking for read only lock file /var/lib/dpkg/lock
E: Couldn't create temporary file to work with /var/lib/apt/lists/us.archive.ubuntu.com_ubuntu_dists_bionic_InRelease - mkstemp (30: Read-only file system)
E: The package lists or status file could not be parsed or opened.
root@ubuntu:/#