Sometimes you can find your rig with the following errors and alike. This is mainly related to flash drive failure. Generally I would replace it after this. But you can try to write system image again.
Sure you can try to recover it and so on but this this requires some linux admin skills and you should not waste time on this, just write image again or throw with flash to the garbage.
Here is another example of a corrupted filesystem. Though it's still running there are some errors on it obviously. And maybe filesystem check failed. For this reason it's mounted in readonly mode, it can even start and run but without logs, lot's of error messages and limited functionality.
If you are at console you will see these errors. But you can notice that configs are not applying, miners do not switch, etc.
Here is how to test if the filesystem is readonly, try to create some file.
echo "test" > /tmp/test.txt
You'll get the following reply with error