The space required is the space that the packages will take up after the complete installation. This is not the space required during installation which will be bigger. For example:
- pkg-1 is installed and takes up 100M (compressed rpm of 50M)
- pkg-2 is an update, and takes up 400M (compressed rpm of 200M)
This means that at the highest point the system will need (theoretical approximation, this also depends whether files remain the same or not, pessimistic scenario here):
- 100M for pkg-1
- 400M for pkg-2 once installed (a brief moment the files of both will be present on the system)
- 200M because probably
yum
still has the compressed pkg-2.rpm untill the installation completely finishes
- maybe some extra log files or other, but that can probably be neglected with respect to 100M.
So in this scenario I think yum
will tell you that the update will need 300M
more space (from 100M to 400M), but at the peak moment 600M will be used.