usage of mount -o remount rw /

please take a look to this question and its answer how to uninstal a program when graphical mode can not load Now I quoted from answer:

Remount the system partition with R/W permission: mount -o remount rw /

Ok.I just know about a bit about mount. Here are my questions:

  1. what is this command and duty?
  2. why we need them ? ( In general or that case, any idea helpful)

mount - mount a filesystem

-o, --options

Options are specified with a -o flag followed by a comma separated string of options.

remount

Attempt to remount an already-mounted filesystem. This is commonly used to change the mount flags for a filesystem, especially to make a readonly filesystem writeable. It does not change device or mount point.

The remount functionality follows the standard way how the mount command works with options from fstab. It means the mount command doesn't read fstab (or mtab) only when a device and dir are fully specified.ManPage


Take a look to RecoveryMode

8.1 The root partition is mounted read-only. To mount it read/write, enter the command

mount -o remount,rw /