Environment variables¶

None of the USBIP_* variables is required, and none changes the USB behaviour of a device - they turn on diagnostics, or tell the C wrappers where to connect.

Variable	Read by	Default	Effect
`USBIP_PCAPNG`	the Python library and both C libraries	unset - off	write every transfer to a PCAPNG capture file
`USBIP_DEBUG`	the device core (Python and C)	unset - off	log every control request (with the verdict) and every data transfer (Python prints to stdout, C to stderr)
`USBIP_HOST`	the C `libusb-1.0` / `libusbK` wrappers only	`127.0.0.1`	which USB/IP server to connect to
`USBIP_PORT`	the C `libusb-1.0` / `libusbK` wrappers only	`3240`	its TCP port

Linux / macOSWindows

USBIP_PCAPNG=traffic.pcapng python3 examples/doc/boot_keyboard.py   # capture
USBIP_DEBUG=1 python3 examples/doc/boot_keyboard.py                 # log requests

set USBIP_PCAPNG=traffic.pcapng
python examples\doc\boot_keyboard.py

USBIP_PCAPNG=1 (or on/yes/true/auto) auto-names the file after the program, in the current directory; %p in the value expands to the process id. Details in Capturing traffic.

These pages write their examples for a POSIX shell. Only the syntax differs:

	Linux / macOS (`sh`)	Windows `cmd`	PowerShell
for one command only	`USBIP_DEBUG=1 prog`	not supported	not supported
for the rest of the session	`export USBIP_DEBUG=1`	`set USBIP_DEBUG=1`	`$env:USBIP_DEBUG = "1"`
unset it again	`unset USBIP_DEBUG`	`set USBIP_DEBUG=`	`Remove-Item Env:USBIP_DEBUG`

One set per line

In cmd, set USBIP_PORT=4000 && prog makes the space before && part of the value, and the connection then fails with nothing obviously wrong in the command.

Substituting the libusb-1.0 / libusbK wrapper for the system library is the one step that is not an environment variable on Windows:

	Linux	macOS	Windows
load the wrapper, not the system libusb	`LD_PRELOAD=/path/to/libusb-1.0.so.0`	`DYLD_LIBRARY_PATH` (SIP blocks `DYLD_INSERT_LIBRARIES`)	copy `libusb-1.0.dll` into the program's own directory, which Windows searches first
find your own shared library at run time	`LD_LIBRARY_PATH`	`DYLD_LIBRARY_PATH`	beside the `.exe`, or on `PATH`

pyusb needs neither: it takes the backend path as an argument.

USBIP_HOST / USBIP_PORT are not read by the Python host

A Python program picks its server in code - usbip.host.open(..., transport=usbip.USBIP(host, port)). The variables exist because a stock libusb or libusbK binary loading a C wrapper has no place to pass one; they matter to Python only when you point pyusb at that wrapper (see pyusb). The wrappers read them once, inside libusb_init() - set them before it runs.