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owhttpd - Man Page

Tiny webserver for 1-wire control


owhttpd [ -c config ] -d serialport | -u | -s [host:]port -p tcp-port



1-wire is a wiring protocol and series of devices designed and manufactured by Dallas Semiconductor, Inc. The bus is a low-power low-speed low-connector scheme where the data line can also provide power.

Each device is uniquely and unalterably numbered during manufacture. There are a wide variety of devices, including memory, sensors (humidity, temperature, voltage, contact, current), switches, timers and data loggers. More complex devices (like thermocouple sensors) can be built with these basic devices. There are also 1-wire devices that have encryption included.

The 1-wire scheme uses a single bus master and multiple slaves on the same wire. The bus master initiates all communication. The slaves can be  individually discovered and addressed using their unique Id.

Bus masters come in a variety of configurations including serial, parallel, i2c, network or USB adapters.

OWFS design

OWFS is a suite of programs that designed to make the 1-wire bus and its devices easily accessible. The underlying principle is to create a virtual filesystem, with the unique Id being the directory, and the individual properties of the device are represented as simple files that can be read and written.

Details of the individual slave or master design are hidden behind a consistent interface. The goal is to  provide an easy set of tools for a software designer to create monitoring or control applications. There  are some performance enhancements in the implementation, including data caching, parallel access to bus  masters, and aggregation of device communication. Still the fundamental goal has been ease of use, flexibility and correctness rather than speed.


owhttpd (1) is a small webserver that shows the Dallas/Maxim 1-Wire bus attached to a serial port. The main view shows the devices found, You can then navigate to individual devices, and view/alter their properties.

owhttpd (1) uses the same naming convention as owfs (1) , where the URL corresponds to the filename.

The web server is a modified version of chttpd by Greg Olszewski. It serves no files from the disk, only virtual files from the 1-wire bus. Security should therefore be good. Only the 1-wire bus is at risk.

Specific Options

-p portnum

Sets the tcp port the web server runs on. Access with the URL http://servernameoripaddress:portnum

If no port is specified, an ephemeral port is selected by the operating system. Use zeroconf (Bonjour) to discover the assigned port.

Device Options (1-wire Bus Master)

These options specify the device (bus master) connecting the computer to the 1-wire bus. The 1-wire slaves are connected to the 1-wire bus, and the bus master connects to a port on the computer and controls the 1-wire bus. The bus master is either an actual physical device, the kernel w1 module, or an owserver (1).

At least one device option is required. There is no default. More than one device can be listed, and all will be used. (A logical union unless you explore the /bus.n/ directories.)

Linux and BSD enforce a security policy restricting access to hardware ports. You must have sufficient rights to access the given port or access will silently fail.

* Serial devices

port specifies a serial port, e.g. /dev/ttyS0 or an USB port accessed as serial port, e.g. /dev/ttyUSB0

If OWFS was built with libftdi support, you may be able to use the ftdi: prefix in any of the options as port to address a FTDI-based USB device.
For details, see the Ftdi Addressing section.

-d port | --device=port (DS2480B)

DS2480B-based bus master (like the DS9097U or an adapter of the LINK family in emulation mode). If the adapter doesn't respond, a passive type (DS9907E or diode/resistor) circuit will be assumed.

--serial_flextime | --serial_regulartime (DS2480B)

Changes details of bus timing (see DS2480B datasheet). Some devices, like the Swart LCD cannot work with flextime.

--baud=1200|9600|19200|38400|57600|115200 (DS2480B,LINK,HA5)

Sets the initial serial port communication speed for all bus masters. Not all serial devices support all speeds. You can change the individual bus master speed for a device of the LINK family and DS2880B in the interface/settings directory. The HA5 speed is set in hardware, so the command line baud rate should match that rate.
Usually the default settings (9600 for a device of the LINK family and DS2480B ) and 115200 for the HA5 are sane and shouldn't be changed.

--straight_polarity  | --reverse_polarity (DS2480B)

Reverse polarity of the DS2480B output transistors? Not needed for the DS9097U, but required for some other designs.

--link=port (LINK)

iButtonLink LINK adapter (all versions) in non-emulation mode. Uses an ascii protocol over serial.
This supports the simplified ftdi:<serial number> addressing scheme.

--ha7e=port (HA7E)

Embedded Data Systems HA7E adapter ( and HA7S ) in native ascii mode.

--ha5=port | --ha5=port:a | --ha5=port:acg (HA5)

Embedded Data Systems HA5 mutidrop adapter in native ascii mode. Up to 26 adapters can share the same port, each with an assigned letter. If no letter specified, the program will scan for the first response (which may be slow).

--checksum | --no_checksum (HA5)

Turn on (default) or off the checksum feature of the HA5 communication.

--passive=port | --ha2=port | --ha3=port | --ha4b=port (Passive)

Passive 1-wire adapters. Powered off the serial port and using passive electrical components (resitors and diodes).

--8bit | --6bit (Passive)

Synthesize the 1-wire waveforme using a 6-bit (default) serial word, or 8-bit word. Not all UART devices support 6 bit operation.


Timeout (in seconds) for all serial communications. 5 second default. Can be altered dynamically under /settings/timeout/serial

* USB devices

The only supported true USB bus masters are based on the DS2490 chip. The most common is the DS9490R which has an included 1-wire Id slave with family code 81.

There are also bus masters based on the serial chip with a USB to serial conversion built in. These are supported by the serial bus master protocol.


DS2490 based bus master (like the DS9490R).


Use the second USB bus master. (The order isn't predicatble, however, since the operating system does not consistently order USB devices).


Use all the USB devices.

--usb_flextime | --usb_regulartime

Changes the details of 1-wire waveform timing for certain network configurations.


Willy Robion's alternative USB timing.


Timeout for USB communications. This has a 5 second default and can be changed dynamically under /settings/timeout/usb

* I2C devices

I2C is  2 wire protocol used for chip-to-chip communication. The bus masters: DS2482-100, DS2482-101 and DS2482-800 can specify (via pin voltages) a subset of addresses on the i2c bus. Those choices are





0x1C,0x1D,0x1E,0x1F (DS2482-800 only)

port for i2c masters have the form /dev/i2c-0, /dev/i2c-1, ...

-d port | --device=port

This simple form only permits a specific port and the first available i2c_address

--i2c=port | --i2c=port:i2c_address | --i2c=port:ALL

Specific i2c port and the i2c_address is either the first, specific, or all or them. The i2c_address is 0,1,2,...

--i2c | --i2c=: | --i2c=ALL:ALL

Search the available i2c buses for either the first, the first, or every i2c adapter.

The DS2482-800 masters 8 1-wire buses and so will generate 8 /bus.n entries.

* Network devices

These bus masters communicate via the tcp/ip network protocol and so can be located anywhere on the network. The network_address is of the form tcp_address:port

E.g. or localhost:3000


LinkHubE network LINK adapter by iButtonLink

--ha7net=network_address | --ha7net

HA7Net network 1-wire adapter with specified tcp address or discovered by udp multicast. By Embedded Data Systems
--timeout_ha7=60 specific timeout for HA7Net communications (60 second default).


Etherweather adapter

-s network_address | --server=network_address

Location of an owserver (1) program that talks to the 1-wire bus. The default port is 4304.


Timeout for network bus master communications. This has a 1 second default and can be changed dynamically under /settings/timeout/network

* Simulated devices

Used for testing and development. No actual hardware is needed. Useful for separating the hardware development from the rest of the software design.


is a list of comma-separated 1-wire devices in the following formats. Note that a valid CRC8 code is created automatically.


Hexadecimal family codes (the DS18S20, DS2405 and DS1921 in this example).


A more complete hexadecimal unique address. Useful when an actual hardware device should be simulated.


The 1-wire device name. (Full Id cannot be speciifed in this format).


Random address and random values for each read. The device Id is also random (unless specified).

--temperature_low=12 --temperature_high=44

Specify the temperature limits for the fake adapter simulation. These should be in the same temperature scale that is specified in the command line. It is possible to change the limits dynamically for each adapter under /bus.x/interface/settings/simulated/[temperature_low|temperature_high]


Predictable address and predictable values for each read. (See the website for the algorhythm).

* w1 kernel module

This a linux-specific option for using the operating system's access to bus masters. Root access is required and the implementation was still in progress as of owfs v2.7p12 and linux 2.6.30.

Bus masters are recognized and added dynamically. Details of the physical bus master are not accessible, bu they include USB, i2c and a number of GPIO designs on embedded boards.

Access is restrict to superuser due to the netlink broadcast protocol employed by w1. Multitasking must be configured (threads) on the compilation.


Use the linux kernel w1 virtual bus master.


Timeout for w1 netlink communications. This has a 10 second default and can be changed dynamically under /settings/timeout/w1

Ftdi Addressing

FTDI is a brand of USB-to-serial chips which are very common. If your serial device is connected via a USB serial dongle based on a FTDI chip, or if your  adapter uses a built-in FTDI USB chip (for example, the LinkUSB), you can use this FTDI addressing.

The main benefit with this mode of access is that we can decrease the communication delay, yielding twice as fast 1-Wire communication in many cases.

The following values for port can be used to identify a specific FTDI port in several of the serial devices options.
Note that this requires that OWFS is built with libftdi support, which might not be the case in standard repositories.


path of bus and device-node (e.g. "003/001") within usb device tree (usually at /proc/bus/usb/ or /dev/bus/usb/)


first device with given vendor and product id, ids can be decimal, octal (preceded by "0") or hex (preceded by "0x")


as above with index being the number of the device (starting with 0) if there are more than one

ftdi:s:<vendor>:<product>:<serial number>

the device with given vendor id, product id and serial number string

The above formats are parsed fully by libftdi (minus the ftdi: prefix).

Simplified device serial-only support

An additional format is supported, for certain bus types. This only specifies the USB serial number.

ftdi:<serial number>

Identifies a FTDI device by serial number only. Currently, this is only valid for the VID/PID found on the LinkUSB (i.e. --link). Note that those VID/PID's are the default for any FT232R device, and in no way exclusive to LinkUSB.


In order to run owserver (1) without root privileges - as you should, you must have sufficient permissions to the raw USB node your adapter is connected to e.g. "003/001" (usually at /proc/bus/usb/ or /dev/bus/usb/).

An easy way to achieve this would be using chown (1):

sudo chown :<your user> /dev/bus/usb/003/001

changes the group of the raw USB node "003/001" from default "root" to "<your user>"

You can also write a udev (1) rule for your adapter:

SUBSYSTEM=="usb", DRIVER=="usb", ATTR{idVendor}=="0403", ATTR{idProduct}=="6001", ATTR{serial}=="AK0048A0", GROUP="owsrv"

saved as a file e.g. "10-FTDI-LinkUSB.rules" in "/etc/udev/rules.d/", this rule will automate the process of changing the group to "owsrv" of the raw USB node the LinkUSB adapter with S/N:AK0048A0 is connected to.

Serial USB node

Communication in FTDI mode accesses the RAW USB node and NOT the serial USB node your OS might have created automatically e.g. /dev/ttyUSB0.
As a side effect, if existing, the serial USB node e.g. /dev/ttyUSB0 is removed on successful starting of owserver (1). After it's termination un- and re-plugging the adapter, or un- and reloading of the module ftdi_sio will recreate the serial USB node.

Examples FTDI addressing

owserver -d ftdi:s:0x0403:0x6001:A800bXHr

starts owserver with a LinkUSB (VID:0x0403,PID:0x6001,S/N:A800bXHr) as bus master in DS2480B-based emulation mode with direct FTDI access

owserver --link=ftdi:A800bXHr

starts owserver with a LinkUSB (S/N:A800bXHr) as bus master identified by serial number only in native mode with direct FTDI access

Temperature Scale Options

-C --Celsius

-F --Fahrenheit

-K --Kelvin

-R --Rankine

Temperature scale used for data output. Celsius is the default.

Can also be changed within the program at /settings/units/temperature_scale

Pressure Scale Options

--mbar (default)






Pressure scale used for data output. Millibar is the default.

Can also be changed within the program at /settings/units/pressure_scale

Format Options

Choose the representation of the 1-wire unique identifiers. OWFS uses these identifiers as unique directory names.

Although several display formats are selectable, all must be in family-id-crc8 form, unlike some other programs and the labelling on iButtons, which are crc8-id-family form.

-f --format=“f[.]i[[.]c]”

Display format for the 1-wire devices. Each device has a 8byte address, consisting of:


family code, 1 byte


Id number, 6 bytes


CRC checksum, 1 byte

Possible formats are f.i (default, 01.A1B2C3D4E5F6), fi fic f.ic f.i.c and fi.c

All formats are accepted as input, but the output will be in the specified format.

The address elements can be retrieved from a device entry in owfs by the family, id and crc8 properties, and as a whole with address. The reversed id and address can be retrieved as r_id and r_address.

Job Control Options

-r --readonly

-w --write

Do we allow writing to the 1-wire bus (writing memory, setting switches, limits, PIOs)? The write option is available for symmetry, it's the default.

-P --pid-file filename

Places the PID -- process Id of owfs into the specified filename. Useful for startup scripts control.

--background | --foreground

Whether the program releases the console and runs in the background after evaluating command line options. background is the default.



default mixed destination: stderr foreground / syslog background


syslog only


stderr only


/dev/null (quiet mode).



default errors only




all high level calls


data summary for each call


details level


debugging chaff

--error_level=9 produces a lot of output

Configuration File

-c file | --configuration file

Name of an owfs (5) configuration file with more command line parameters

Help Options

See also this man page and the web site http://www.owfs.org

-h --help=[device|cache|program|job|temperature]

Shows basic summary of options.


1-wire bus master options


cache and communication size and timing


mountpoint or TCP server settings


control and debugging options


Unique Id display format and temperature scale

-V --version

Version of this program and related libraries.

Time Options

Timeouts for the bus masters were previously listed in Device options. Timeouts for the cache affect the time that data stays in memory. Default values are shown.


Seconds until a volatile property expires in the cache. Volatile properties are those (like temperature) that change on their own.

Can be changed dynamically at /settings/timeout/volatile


Seconds until a stable property expires in the cache. Stable properties are those that shouldn't change unless explicitly changed. Memory contents for example.

Can be changed dynamically at /settings/timeout/stable


Seconds until a directory listing expires in the cache. Directory lists are the 1-wire devices found on the bus.

Can be changed dynamically at /settings/timeout/directory


Seconds until the presence and bus location of a 1-wire device expires in the cache.

Can be changed dynamically at /settings/timeout/presence

There are also timeouts for specific program responses:


Seconds until the expected response from the owserver (1) is deemed tardy.

Can be changed dynamically at /settings/timeout/server


Seconds that an ftp session is kept alive.

Can be changed dynamically at /settings/timeout/ftp


owhttpd -p 3001 -d /dev/ttyS0

Web server runs on tcp port 3001, serial adapter at ttyS0

owhttpd -p 3001 -s littlehost:4304 --error_level=3

Web server on port 3001, from owserver process on host "littlehost", extensive error messages.

owhttpd -p 3001 -u -u2 -r

Read-only web server on port 3001, using two usb adapters.



See Also


owfs (1) owhttpd (1) owftpd (1) owserver (1) owdir (1) owread (1) owwrite (1) owpresent (1) owtap (1)

Configuration and testing

owfs (5) owtap (1) owmon (1)

Language bindings

owtcl (3) owperl (3) owcapi (3)


DS1427 (3) DS1904(3) DS1994 (3) DS2404 (3) DS2404S (3) DS2415 (3) DS2417 (3)


DS2401 (3) DS2411 (3) DS1990A (3)


DS1982 (3) DS1985 (3) DS1986 (3) DS1991 (3) DS1992 (3) DS1993 (3) DS1995 (3) DS1996 (3) DS2430A (3) DS2431 (3) DS2433 (3) DS2502 (3) DS2506 (3) DS28E04 (3) DS28EC20 (3)


DS2405 (3) DS2406 (3) DS2408 (3) DS2409 (3) DS2413 (3) DS28EA00 (3)


DS1822 (3) DS1825 (3) DS1820 (3) DS18B20 (3) DS18S20 (3) DS1920 (3) DS1921 (3) DS1821 (3) DS28EA00 (3) DS28E04 (3)


DS1922 (3)


DS2450 (3)


DS2890 (3)

Multifunction (current, voltage, temperature)

DS2436 (3) DS2437 (3) DS2438 (3) DS2751 (3) DS2755 (3) DS2756 (3) DS2760 (3) DS2770 (3) DS2780 (3) DS2781 (3) DS2788 (3) DS2784 (3)


DS2423 (3)

LCD Screen

LCD (3) DS2408 (3)


DS1977 (3)


DS2406 (3) -- TAI8570


Paul Alfille (paul.alfille@gmail.com)

Referenced By

DS1821(3), DS1822(3), DS1825(3), DS18B20(3), DS18S20(3), DS1921(3), DS1963L(3), DS1963S(3), DS1977(3), DS1991(3), DS1992(3), DS1993(3), DS1995(3), DS1996(3), DS2401(3), DS2404(3), DS2405(3), DS2406(3), DS2408(3), DS2409(3), DS2413(3), DS2415(3), DS2423(3), DS2430A(3), DS2431(3), DS2433(3), DS2436(3), DS2437(3), DS2438(3), DS2450(3), DS2502(3), DS2505(3), DS2506(3), DS2720(3), DS2740(3), DS2751(3), DS2755(3), DS2760(3), DS2770(3), DS2780(3), DS2781(3), DS2890(3), DS28E04(3), DS28EA00(3), DS28EC20(3), EDS(3), EEEF(3), IBLSS(3), InfernoEmbedded(3), LCD(3), mAM001(3), mCM001(3), mDI001(3), mRS001(3), owcapi(1), owfs(1), owfs(5), owftpd(1), owmon(1), ownet(1), owperl(3), owserver(1), owshell(1), owtap(1), owtcl(n).

2004 OWFS Manpage One-Wire File System