RHEL 6 Virtualization - 19.3. Transport modes

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19.3. Transport modes

For remote management, libvirt supports the following transport modes:

Transport Layer Security (TLS)

Transport Layer Security TLS 1.0 (SSL 3.1) authenticated and encrypted TCP/IP socket, usually listening on a public port number. To use this you will need to generate client and server certificates. The standard port is 16514.

UNIX sockets

Unix domain sockets are only accessible on the local machine. Sockets are not encrypted, and use UNIX permissions or SELinux for authentication. The standard socket names are /var/run/libvirt/libvirt-sock and /var/run/libvirt/libvirt-sock-ro (for read-only connections).

SSH

Transported over a Secure Shell protocol (SSH) connection. Requires Netcat (the nc package) installed. The libvirt daemon (libvirtd) must be running on the remote machine. Port 22 must be open for SSH access. You should use some sort of ssh key management (for example, the ssh-agent utility) or you will be prompted for a password.

ext

The ext parameter is used for any external program which can make a connection to the remote machine by means outside the scope of libvirt. This parameter is unsupported.

tcp

Unencrypted TCP/IP socket. Not recommended for production use, this is normally disabled, but an administrator can enable it for testing or use over a trusted network. The default port is 16509.

The default transport, if no other is specified, is tls.

Remote URIs

A Uniform Resource Identifier (URI) is used by virsh and libvirt to connect to a remote host. URIs can also be used with the --connect parameter for the virsh command to execute single commands or migrations on remote hosts.

libvirt URIs take the general form (content in square brackets, "[]", represents optional functions):

driver[+transport]://[username@][hostname][:port]/[path][?extraparameters]

The transport method or the hostname must be provided to target an external location.

Examples of remote management parameters

Connect to a remote KVM host named server7, using SSH transport and the SSH username ccurran.
```
qemu+ssh://[email protected]/
```
Connect to a remote KVM hypervisor on the host named server7 using TLS.
```
qemu://server7/
```
Connect to a remote KVM hypervisor on host server7 using TLS. The no_verify=1 instructs libvirt not to verify the server's certificate.
```
qemu://server7/?no_verify=1
```

Testing examples

Connect to the local KVM hypervisor with a non-standard UNIX socket. The full path to the Unix socket is supplied explicitly in this case.
```
qemu+unix:///system?socket=/opt/libvirt/run/libvirt/libvirt-sock
```
Connect to the libvirt daemon with an unencrypted TCP/IP connection to the server with the IP address 10.1.1.10 on port 5000. This uses the test driver with default settings.
```
test+tcp://10.1.1.10:5000/default
```

Extra URI parameters

Extra parameters can be appended to remote URIs. The table below Table 19.1, “Extra URI parameters” covers the recognized parameters. All other parameters are ignored. Note that parameter values must be URI-escaped (that is, a question mark (?) is appended before the parameter and special characters are converted into the URI format).

Table 19.1. Extra URI parameters

Name	Transport mode	Description	Example usage
name	all modes	The name passed to the remote virConnectOpen function. The name is normally formed by removing transport, hostname, port number, username and extra parameters from the remote URI, but in certain very complex cases it may be better to supply the name explicitly.	name=qemu:///system
command	ssh and ext	The external command. For ext transport this is required. For ssh the default is ssh. The PATH is searched for the command.	command=/opt/openssh/bin/ssh
socket	unix and ssh	The path to the UNIX domain socket, which overrides the default. For ssh transport, this is passed to the remote netcat command (see netcat).	socket=/opt/libvirt/run/libvirt/libvirt-sock
netcat	ssh	The `netcat` command can be used to connect to remote systems. The default netcat parameter uses the `nc` command. For SSH transport, libvirt constructs an SSH command using the form below: `command` -p `port` [-l `username`] `hostname` `netcat` -U socket The `port`, `username` and `hostname` parameters can be specified as part of the remote URI. The `command`, `netcat` and `socket` come from other extra parameters.	netcat=/opt/netcat/bin/nc
no_verify	tls	If set to a non-zero value, this disables client checks of the server's certificate. Note that to disable server checks of the client's certificate or IP address you must change the libvirtd configuration.	no_verify=1
no_tty	ssh	If set to a non-zero value, this stops ssh from asking for a password if it cannot log in to the remote machine automatically (for using ssh-agent or similar). Use this when you do not have access to a terminal - for example in graphical programs which use libvirt.	no_tty=1