USB devices are shared among Citrix Receiver and the Linux VDA desktop. Once a USB device is redirected to the desktop, the user can use the USB device as if it were locally connected.
USB redirection includes three main areas of functionality:
- open source project implementation (VHCI)
- VHCI service
- USB service
Open source VHCI
This portion of the USB redirection feature develops a general USB device sharing system over an IP network. It consists of a Linux kernel driver and some user mode libraries that allow you to communicate with the kernel driver to get all the USB data. In the Linux VDA implementation, Citrix reuses the kernel driver of VHCI. However, all the USB data transfers between Linux VDA and Citrix Receiver are encapsulated in the Citrix ICA protocol package.
The VHCI service is an open source service provided by Citrix to communicate with the VHCI kernel module. This service works as a gateway between VHCI and the Citrix USB service.
The USB service represents a Citrix module that manages all the virtualization and data transfers on the USB device.
How USB redirection works
Typically, if a USB device is redirected successfully to the Linux VDA, one or more device nodes are created in the system /dev path. However, in some cases the redirected device cannot be used by an active Linux VDA session. USB devices rely on drivers to function properly (and some devices require special drivers), and in some cases drivers are not provided, which results in some redirected USB devices being inaccessible to an active Linux VDA session. When situations like these occur, the drivers must be installed and the system must be configured properly to ensure USB device connectivity.
The Linux VDA supports a list of USB devices that are successfully redirected to and from the client. In addition, the device is properly mounted, especially the USB disk, allowing the user to access the disk without any additional configuration.
Configure USB redirection
A Citrix policy controls whether USB device redirection is enabled or disabled. In addition, the type of device can also be specified using a Delivery Controller policy. When configuring USB redirection for the Linux VDA, the following policy and rules must be configured:
- Client USB device redirection policy
- Client USB device redirection rules
Enable USB redirection policy
In Citrix Studio, enable (or disable) USB device redirection to and from the client (for workstation hosts only).
In the Edit Setting dialog:
- Select Allowed.
- Click OK.
Set USB redirection rules
After enabling the USB redirection policy, set redirection rules using Citrix Studio by specifying which devices are allowed (or denied) on the Linux VDA.
In the Client USB device redirection rules dialog:
- Click New to add a redirection rule, or click Edit to review an existing rule.
- After creating (or modifying) a rule, click OK.
For more information about configuring generic USB redirection, see Citrix Generic USB Redirection Configuration Guide.
Troubleshoot USB redirection issues
Use the information in this section to troubleshoot various issues that you might encounter when using the Linux VDA.
No devices on the Receiver toolbar
In some cases, you might not be able to see devices listed on the Citrix Receiver toolbar, which indicates that no USB redirection is taking place. If this occurs, verify the following:
- the policy is configured to allow USB redirection
- the Kernel module is compatible with your kernel
USB devices can be seen in the Receiver toolbar, but are labeled policy restricted, which results in failed redirection
This issue occurs because of the device's policy configuration. In such cases:
- configure the Linux VDA policy to enable redirection
- Verify whether any additional policy restrictions are configured in the Receiver registry; a device might be blocked by the Receiver registry setting. Check DeviceRules in the registry path to ensure that the device is not denied access by this setting:
For more information, see How to Configure Automatic Redirection of USB Devices on the Citrix Support site.
A USB device is redirected successfully, but I cannot use it in my session
In most cases, only USB devices in the supported devices list can be redirected. However, in some cases other kinds of devices might be redirected into an active Linux VDA session. In these situations, for every redirected device, a node owned by the user is created in the system /dev path. However, it is the drivers and the configuration that determine whether the user can use the device successfully. If you find a device owned (plugged in) but inaccessible, add the device to an unrestricted policy.
In the case of USB drives, the Linux VDA configures and mounts the disk. The user (and only the owner who installed it) can access the disk without any additional configuration. This might not be the case for devices that are not in the supported device list.
Build the VHCI kernel module
USB redirection depends on the VHCI kernel modules (usb-vhci-hcd.ko and usb-vhci-iocif.ko). These modules are part of the Linux VDA distribution (as part of the RPM package). They are compiled based on the official Linux distribution kernels and are noted in the table below:
|Supported Linux distribution
|| Kernel version
If the kernel of your machine is not compatible with the driver built by Citrix for the Linux VDA, the USB service might fail to start. In this case you cannot use the USB redirection feature unless you build your own VHCI kernel modules.
Verify whether your kernel is consistent with the modules built by Citrix
On the command line, execute the following command to verify whether the kernel is consistent:
If the command executes successfully, the kernel module has loaded successfully and the version is consistent with the one installed by Citrix.
If the command executes with errors, the kernel is inconsistent with the Citrix module and must be rebuilt.
Rebuild the VHCI kernel module
If your kernel module is inconsistent with the Citrix version, do the following:
1. Download the LVDA source code from the Citrix download site. Select the file contained in the section "Linux Virtual Delivery Agent (sources)."
2. Restore files from the citrix-linux-vda-sources.zip file; you can get VHCI source files in linux-vda-souces/vhci-hcd-1.15.tar.bz2; you can restore VHCI files using tar xvf vhci-hcd-1.15.tar.bz2.
3. Build the kernel module based on the header files and the Module.symvers file. Use the following steps to install the kernel header files and create Module.symvers based on the appropriate Linux distribution:
RHEL 7.3/RHEL 7.2
zypper install kernel-devel
zypper install kernel-source
zypper install kernel-source
apt-get install linux-headers
If the installation is successful, there will be a kernel folder resembling:
4. In the folder (/usr/src/kernels/3.10.0-327.10.1.el7.x86_64), verify that the file Module.symvers is present. If this file is not in the folder, you must build the kernel to get this file (e.g., make oldconfig; make prepare;make modules;make) or copy it from /usr/src/kernels/3.10.0-327.10.1.el7.x86_64-obj/x86_64/defaults/module.*
5. In the file vhci-hcd-1.15/Makefile, change the Makefile of VCHI and set KDIR to the kernel directory:
#KDIR = $(BUILD_PREFIX)/lib/modules/$(KVERSION)/build
KDIR = /usr/src/kernels/3.10.0-327.10.1.el7.x86_64
6. In the folder vhci-hcd-1.15/, run make to build the VHCI kernel.
If the build was successful, usb-vhci-hcd.ko and usb-vhci-iocifc.ko are created in the vhci-hcd-1.15/ folder.
7. Replace the kernel module with the newly built one: cp -f usb-vhci-*.ko /opt/Citrix/VDA/lib64/
8. Restart the USB service: service ctxusbsd restart
9. Log off and log on to the the session again. Check to see if USB redirection is functioning.
The following devices have been verified to work with this version of the Linux VDA. Other devices might be freely used, with unexpected results:
|USB mass storage device
|Netac Technology Co., Ltd
|Kingston Datatraveler 101 II
|Kingston Datatraveler GT101 G2
|SanDisk SDCZ80 flash drive
|SanDisk Cruzer 16GB
|USB 3D mouse
|3DConnexion SpaceMouse Pro
|Epson Perfection V330 photo
Unable to unmount the redirected USB disk. For the access control of all USB disks redirected from Citrix Receiver, the Linux VDA manages all of these devices under administrative privilege to ensure that only the owner can access the redirected device. As a result, the user is not permitted to unmount the device without the administrative privilege.
File lost when you stop redirecting a USB disk. If you redirect a USB disk into a session and try to modify it (for example, create some files on the disk), then stop redirecting it immediately using the Receiver toolbar, the file you modified (or created) can be lost.
This issue occurs because when you write data to a file system, the system mounts the memory cache in the file system, the data is not actually written to the disk itself. If you stop redirecting using the Receiver toolbar, there is no time remaining for the data being flushed into the disk, which results in lost data.
To resolve this issue, whenever you write data into the disk, use the sync command in a terminal to flush data into the disk, then stop USB redirection.