[A recent breaking change upstream in Golang's crypto
library](e4e2799dd7)
has broken SSH connectivity for a few builders:
```
==> qemu: Waiting for SSH to become available...
2017/05/20 16:23:58 ui: ==> qemu: Waiting for SSH to become available...
2017/05/20 16:23:58 packer: 2017/05/20 16:23:58 [INFO] Attempting SSH connection...
2017/05/20 16:23:58 packer: 2017/05/20 16:23:58 reconnecting to TCP connection for SSH
2017/05/20 16:23:58 packer: 2017/05/20 16:23:58 handshaking with SSH
2017/05/20 16:23:58 packer: 2017/05/20 16:23:58 handshake error: ssh: must specify HostKeyCallback
2017/05/20 16:23:58 packer: 2017/05/20 16:23:58 [DEBUG] SSH handshake err: ssh: must specify HostKeyCallback
2017/05/20 16:24:05 packer: 2017/05/20 16:24:05 [INFO] Attempting SSH connection...
2017/05/20 16:24:05 packer: 2017/05/20 16:24:05 reconnecting to TCP connection for SSH
2017/05/20 16:24:05 packer: 2017/05/20 16:24:05 handshaking with SSH
2017/05/20 16:24:05 packer: 2017/05/20 16:24:05 handshake error: ssh: must specify HostKeyCallback
2017/05/20 16:24:05 packer: 2017/05/20 16:24:05 [DEBUG] SSH handshake err: ssh: must specify HostKeyCallback
```
Specifying HostKeyCallback as insecure should make things work again
and would make sense for packer's use case.
If using a builder that has an http server set up for file transfer,
expose the connection info to the shell provisioner through the environment
variable PACKER_HTTP_ADDR.
Closes#2869
Add support for using ctrl, shift and alt as key modifiers. So you can now achieve ctrl+c by using "<leftCtrlOn>c<leftCtrlOff>".
Updated documentation for new key stroke tokens.
When debugging a build (or maintaining an existing packer file), teach `packer build -debug` how to step through individual `boot_command`s in order to triage the packer file.
Prevalidates hardware resources on Linux platforms for Virtualbox and
VMware builders. This is currently only available on Linux, as enabling
for both Darwin and Windows platforms, relies on cgo bindings that would
prevent effective cross-compilation.
Packer will now fail to build and validate templates if the template is
requesting that the VM to be created would allocate more system
resources than the host system has available.
This _however_ doesn't catch parallel builds that overflow the hosts
resources, will probably still need a better error message for VM's
failing to boot in that case.
Example Outputs:
```
$ $GOPATH/bin/packer build -debug ./vmware-iso.json
Debug mode enabled. Builds will not be parallelized.
vmware-iso output will be in this color.
2 error(s) occurred:
* Unavailable Resources: RAM - Requested - 204800000MB - Available 21721MB
* Unavailable Resources: Disk - Requested - 4000000000MB - Available 76701MB
```
```
$ $GOPATH/bin/packer build -debug ./vbox-iso.json
Debug mode enabled. Builds will not be parallelized.
virtualbox-iso output will be in this color.
2 error(s) occurred:
* Unavailable Resources: RAM - Requested - 10240000MB - Available 21721MB
* Unavailable Resources: Disk - Requested - 1000000000MB - Available 76701MB
```
