Configure USB redirection

USB devices are shared between Citrix Receiver and the Linux VDA desktop. When 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 the Linux VDA and Citrix Receiver are encapsulated in the Citrix ICA protocol package.

VHCI service:

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.

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. Sometimes, however, the redirected device is not usable for an active Linux VDA session. USB devices rely on drivers to function properly and some devices require special drivers. If drivers are not provided, the redirected USB devices are inaccessible to the active Linux VDA session. To ensure USB device connectivity, install the drivers and configure the system properly.

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.

Supported USB devices

The following devices have been verified to support this version of the Linux VDA. Other devices might be freely used, with unexpected results:

Note:

The Linux VDA supports only USB 2.0 protocols.

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, configure the following policy and rules:

• 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:

1. Select Allowed.
2. 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:

1. Click New to add a redirection rule, or click Edit to review an existing rule.
2. After creating (or editing) a rule, click OK.

For more information about configuring generic USB redirection, see Citrix Generic USB Redirection Configuration Guide.

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 following table:

Important:

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 can use the USB redirection feature only if you build your own VHCI kernel modules.

Verify whether your kernel is consistent with the modules built by Citrix

On the command line, run the following command to verify whether the kernel is consistent:

insmod /opt/Citrix/VDA/lib64/usb-vhci-hcd.ko
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If the command runs successfully, the kernel module has loaded successfully and the version is consistent with the one installed by Citrix.

If the command runs 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 6.9/RHEL 6.6:

   yum install kernel-devel
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   SUSE 12.2:

   zypper install kernel-devel
   
   zypper install kernel-source
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   SUSE 11.4:

   zypper install kernel-source
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   Ubuntu 16.04:

   apt-get install linux-headers
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   Tip:

   If the installation is successful, there is a kernel folder resembling:

   /usr/src/kernels/3.10.0-327.10.1.el7.x86_64

4. In the /usr/src/kernels/3.10.0-327.10.1.el7.x86_64 folder, verify that the Module.symvers file is present. If this file is not in the folder, build the kernel to get this file (for example, 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 vhci-hcd-1.15/Makefile file, 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
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6. In the folder vhci-hcd-1.15/, run make to build the VHCI kernel.

   Note:

   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 back on to the session again. Check whether USB redirection is functioning.

Troubleshoot USB redirection issues

Use the information in this section to troubleshoot various issues that you might encounter when using the Linux VDA.

Unable to unmount the redirected USB disk

For the access control of all USB disks redirected from Citrix Receiver, the Linux VDA manages all these devices under administrative privilege to ensure that only the owner can access the redirected device. As a result, the user cannot unmount the device without the administrative privilege.

File lost when you stop redirecting a USB disk

If you redirect a USB disk to a session and try to modify it (for example, create some files on the disk), then stop redirecting it immediately using the toolbar of Citrix Receiver, 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 written to the disk itself. If you stop redirecting using the toolbar of Citrix Receiver, there is no time remaining for the data being flushed to the disk, which results in lost data. To resolve this issue, use the sync command in a terminal to flush data to the disk before stopping USB redirection.

No devices in the toolbar of Citrix Receiver

Sometimes, you might not be able to see devices listed in the toolbar of Citrix Receiver, which indicates that no USB redirection is taking place. If you encounter the issue, verify the following:

• The policy is configured to allow USB redirection
• The Kernel module is compatible with your kernel

Note:

The Devices tab is not available in Citrix Receiver for Linux.

Failed redirection when USB devices can be seen in the toolbar of Citrix Receiver, but are labeled policy restricted

This issue occurs due to the device’s policy configuration. In such cases:

• Configure the Linux VDA policy to enable redirection

• Check whether any additional policy restrictions are configured in the registry of Citrix Receiver. A device might be blocked by the registry setting of Citrix Receiver. Check DeviceRules in the registry path to ensure that the device is not denied access by this setting:

  HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Citrix\ICA Client\GenericUSB

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

Usually, only supported USB devices can be redirected. Sometimes, however, other kinds of devices might be redirected to 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.

Note:

In 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.