If you've found this post and are rushing to upgrade a previously installed version of geth on Linux before the hard fork on October 16th here are a quick set of instructions.
The instructions assume you've built your geth from source. If that is the case the following should be helpful.
Make sure to stop your current geth instance. I used the following command:
$ kill -INT $(pgrep geth)
Find where you cloned the go-ethereum repo. It will be a directory called "go-ethereum".
Enter the following commands:
$ cd go-ethereum $ git fetch $ git pull $ make geth
Once in the directory the "git fetch" command fetches the new branches from the git repository. The "git pull" command updates your "master branch". The "make geth" builds your new version.
I've just upgraded a geth instance running on an EC2 box using the above instructions and had no issues.
Run "geth version" to verify that you have the latest version.
$ ./build/bin/geth version Geth Version: 1.7.3-unstable Git Commit: e9295163aa25479e817efee4aac23eaeb7554bba Architecture: amd64 Protocol Versions: [63 62] Network Id: 1 Go Version: go1.7.5 Operating System: linux GOPATH= GOROOT=/usr/lib/golang