Ubuntu – How much space does Ubuntu take up after it’s already installed

You can use two commands: df and du.

df - report file system disk space usage

Usage works like such:

df -h

Which should output something like this:

Filesystem            Size  Used Avail Use% Mounted on
/dev/vzfs              20G  3.5G   16G  18% /

The -h flag provides human readable output (which makes reading of the output - easier).

du - estimate file space usage

A second tool is with du which is a slower approach but will give you a better break down of a per directory. Information on that can be found in How to determine where the biggest files/directories on my system are stored?

Yes, the "Install Ubuntu alongside Windows 7" option will install Ubuntu in the free, unallocated space, provided that it can be created as a partition (for example, if you already have 4 primary partitions + unpartitioned space, Ubuntu will not be able to install).

The "Install Ubuntu alongside Windows 7" will usually reserve space for a swap partition. This space is usually the size of your RAM. So, for example, if your RAM is 4GB, then picking the "alongside" option will automatically partition your 20GB unpartitioned space to 16GB for the root partition (Ubuntu), and 4GB for swap.