1.fdisk -l to check whether the hard disk exists
2. Create a new folder mkdir /disk to mount the hard disk (if you want to mount to an existing directory, do not create a new one)
3. Mount the hard disk: mount /dev/sdc /disk
4. The mount is successful without reporting an error
5. I want to copy the folder on the server to the hard disk and use cp to copy: cp -r /etc /disk
6. But at this moment an error was reported: cp:cannot create directory '/disk/sdc':Read-only file system
7. I found a way on the Internet, saying that it can be changed to read-write mode when mounting: mount -o remount,rw /dev/sdc /disk
8. But an error was reported when running this command: mount :you must specify the filesystem type (meaning you need to specify the type of filesystem)
9. Later, after consulting my colleagues, the hard disk that was originally mounted is the ntfs file system. It is mounted in the linux folder and it is in read-only mode.
10. Later, format the hard disk as ext file system: mkfs.ext3 /dev/sdc (operate with caution, back up important files first)
11. Then specify the file system type to mount: mount -t ext3 /dev/sdc /disk
So the problem is solved.