I'm using LVM on a system I set up a few years ago. At the time I left some unpartitioned space on the drive so I could create LVM snapshots.
I've now forgotten how much space I set aside.
How can I see how much is free?
Run the /usr/sbin/vgs command. It will list all the LVM volume groups, the total size of each one and the amount of free space.
In addition to sagi's correct answer, as a more general way to help yourself with this, you can just type
You can then type help to see all the lvm commands, this is a good way to help keep all these commands straight.