When /tmp is read only, we can fix that without rebooting the server using the steps below :
umount /tmp
umount -l /tmp (umount -l forces an umount, even if it’s busy)
df -h
fsck -yf /dev/sda2 (y = answer yes to everything)
fsck -yf /dev/sda2 (run it a second time to double check)
df -h
mount /dev/sda2 /tmp
touch /tmp/hello