Solve the problem that/etc/fstab cannot be saved

There is a disk partition mounted to two directories, and umount-a is directly executed to detach two mounts. after the/etc/fstab configuration is not cleared, vi is enabled and/etc/fstab is enabled, restore to the original format, but the prompt "-- INSERT -- w10: Warning: Changingareadonlyfile" is displayed when the file is saved.

There is a disk partition mounted to two directories, and umount-a is directly executed to detach two mounts. the configuration in/etc/fstab is not cleared.

Vi, after opening/etc/fstab, restores it to the original format, but the prompt is displayed when it is saved.
-- INSERT -- w10: Warning: Changing a readonly file
Prompt when saving after modification
"Fstab" E212: Can't open file for writing
: W! It's useless.

It seems that mount is readonly.
Therefore
Root # mount-o remount, rw/

Try vim/etc/fstab to save it.