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developer/services/qrexec-internals.md
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@ -15,21 +15,27 @@ redirect_from:
A [general introduction](/doc/qrexec/) to qrexec is also available.
For the implementation of qrexec2, see [here](/doc/qrexec2/#qubes-rpc-internals).*)
Qrexec framework consists of a number of processes communicating with each other using common IPC protocol (described in detail below).
Components residing in the same domain (`qrexec-client-vm` to `qrexec-agent`, `qrexec-client` to `qrexec-daemon`) use pipes as the underlying transport medium, while components in separate domains (`qrexec-daemon` to `qrexec-agent`, data channel between `qrexec-agent`s) use vchan link.
The qrexec framework consists of a number of processes communicating with each other using common IPC protocol (described in detail below).
Components residing in the same domain (`qrexec-client-vm` to `qrexec-agent`, `qrexec-client` to `qrexec-daemon`) use local sockets as the underlying transport medium.
Components in separate domains (`qrexec-daemon` to `qrexec-agent`, data channel between `qrexec-agent`s) use vchan links.
Because of [vchan limitation](https://github.com/qubesos/qubes-issues/issues/951), it is not possible to establish qrexec connection back to the source domain.
## Dom0 tools implementation
* `/usr/lib/qubes/qrexec-daemon`: One instance is required for every active domain. Responsible for:
### qrexec-daemon
* `/usr/sbin/qrexec-daemon`: One instance is required for every active domain. Responsible for:
* Handling execution and service requests from **dom0** (source: `qrexec-client`).
* Handling service requests from the associated domain (source: `qrexec-client-vm`, then `qrexec-agent`).
* Command line: `qrexec-daemon domain-id domain-name [default user]`
* `domain-id`: Numeric Qubes ID assigned to the associated domain.
* `domain-name`: Associated domain name.
* `default user`: Optional. If passed, `qrexec-daemon` uses this user as default for all execution requests that don't specify one.
* `/usr/lib/qubes/qrexec-policy`: Internal program used to evaluate the RPC policy and deciding whether a RPC call should be allowed.
* `/usr/lib/qubes/qrexec-client`: Used to pass execution and service requests to `qrexec-daemon`. Command line parameters:
### qrexec-policy
* `/usr/bin/qrexec-policy`: Internal program used to evaluate the RPC policy and deciding whether a RPC call should be allowed.
### qrexec-client
* `/usr/bin/qrexec-client`: Used to pass execution and service requests to `qrexec-daemon`. Command line parameters:
* `-d target-domain-name`: Specifies the target for the execution/service request.
* `-l local-program`: Optional. If present, `local-program` is executed and its stdout/stdin are used when sending/receiving data to/from the remote peer.
* `-e`: Optional. If present, stdout/stdin are not connected to the remote peer. Only process creation status code is received.
@ -40,11 +46,12 @@ Because of [vchan limitation](https://github.com/qubesos/qubes-issues/issues/951
## VM tools implementation
* `qrexec-agent`: One instance runs in each active domain. Responsible for:
### `qrexec-agent`: One instance runs in each active domain. Responsible for:
* Handling service requests from `qrexec-client-vm` and passing them to connected `qrexec-daemon` in dom0.
* Executing associated `qrexec-daemon` execution/service requests.
* Command line parameters: none.
* `qrexec-client-vm`: Runs in an active domain. Used to pass service requests to `qrexec-agent`.
### `qrexec-client-vm`: Runs in an active domain. Used to pass service requests to `qrexec-agent`.
* Command line: `qrexec-client-vm target-domain-name service-name local-program [local program arguments]`
* `target-domain-name`: Target domain for the service request. Source is the current domain.
* `service-name`: Requested service name.
@ -52,7 +59,7 @@ Because of [vchan limitation](https://github.com/qubesos/qubes-issues/issues/951
## Qrexec protocol details
Qrexec protocol is message-based.
The qrexec protocol is message-based.
All messages share a common header followed by an optional data packet.
/* uniform for all peers, data type depends on message type */

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developer/services/qrexec.md
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@ -66,6 +66,8 @@ Thus, it is usually more convenient to use `qvm-run`.
There can be an almost arbitrary number of `qrexec-client` processes for a given domain.
The limiting factor is the number of available vchan channels, which depends on the underlying hypervisor, as well the domain's OS.
For more details on the qrexec framework and protocol, see "[Qubes RPC internals](/doc/qrexec-internals)."
## Qubes RPC services
Some common tasks (like copying files between VMs) have an RPC-like structure: a process in one VM (say, the file sender) needs to invoke and send/receive data to some process in other VM (say, the file receiver).