| Original author(s) | Hannu Savolainen |
|---|---|
| Developer(s) | NCR Corporation |
| Stable release | 4.2 build 2019 / March 5, 2019 [1] |
| Operating system | Cross-platform [2] |
| Type | Audio |
| License |
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| Website | www |
The Open Sound System (OSS) is an interface for making and capturing sound in Unix and Unix-like operating systems. It is based on standard Unix devices system calls (i.e. POSIX read, write, ioctl, etc.). The term also sometimes refers to the software in a Unix kernel that provides the OSS interface; it can be thought of as a device driver (or a collection of device drivers) for sound controller hardware. The goal of OSS is to allow the writing of sound-based applications that are agnostic of the underlying sound hardware.
OSS was created by Hannu Savolainen and is distributed under four license options, three of which are free software licences, thus making OSS free software. [3]
The API is designed to use the traditional Unix framework of open(), read(), write(), and ioctl(), via device files. For instance, the default device for sound input and output is /dev/dsp. Examples using the shell:
cat /dev/random > /dev/dsp # plays white noise through the speaker cat /dev/dsp > a.a # reads data from the microphone and copies it to file a.a
OSS implements the /dev/audio interface. Detailed access to individual sound devices is provided via the /dev/oss directory. OSS also has MIDI support in /dev/sequencer, /dev/music (both legacy) and /dev/mini. [4] [5]
On Linux, OSS4 is also able to emulate ALSA, its open-source replacement. [6]
OSS was originally "VoxWare", a Linux kernel sound driver by Hannu Savolainen. Savolainen made the code available under free software licenses, GPL for Linux and BSD for BSD distributions. Between November 1993 (and Linux 1.00) [7] and 1997, OSS was the sole choice of sound system in FreeBSD and Linux. This was changed when Luigi Rizzo wrote a new "pcm" driver for FreeBSD in 1997, and when Jaroslav Kysela started Advanced Linux Sound Architecture in 1998. [8]
In 2002, Savolainen was contracted by the company 4Front Technologies and made the upcoming OSS 4, which includes support for newer sound devices and improvements, proprietary. In response, the Linux community abandoned the OSS/free implementation included in the kernel and development effort switched to the replacement Advanced Linux Sound Architecture (ALSA). FreeBSD by this time had switched to a "newpcm" project started in 1999 and was not affected. [8]
In July 2007, 4Front Technologies released sources for OSS under CDDL-1.0 for OpenSolaris and GPL-2.0-only for Linux. Drivers for some soundcards remained closed-source and were not included in the release. [3] In January 2008, 4Front Technologies released OSS for FreeBSD (and other BSD systems) under the BSD-2-Clause. [9]
OSS4 now exists mostly as a standalone piece of software, not integrated into the kernel source code. The exception is Solaris and OpenSolaris, which use a fork of OSS4 called Boomer. It combines the OSS4 framework (audio and mixer) together with Sun's earlier SADA (/dev/audio) API. [10]
Although Linux distributions such as Ubuntu made OSS4 available as a software package after it was made free software, they have chosen to ignore any bugs filed against these packages. [11]
The OSS API has remained influential despite the obscurity of the original library. NetBSD's documentation describes it as "the preferred API in FreeBSD and Solaris". [12]
FreeBSD contains an independently developed implementation of the OSS API, which includes, among other things, in-kernel resampling, mixing (vchans), equalizer, surround sound, and independent volume control for each application. It also supports bit-perfect mode. [13] It gradually evolved from the "newpcm" replacement written in 1999 and caught up with OSS4 API around 2005. [8]
NetBSD supports a compatibility mode for the OSS API, by providing the soundcard.h header file and the libossaudio library, which internally operate using the native Sun-like audio interface. The replacement was first seen in NetBSD 1.3 of 1998. [12]
Linux had, as aforementioned, switched to Advanced Linux Sound Architecture since 2003 (kernel 2.6). ALSA provides an optional, in-kernel, OSS emulation mode that appears to programs as if it were OSS. [14] ALSA also has a aoss userspace program that works by intercepting systems calls directed to the OSS device files. [15]
OSS/3D is a plugin for music players, which acts as an audio postprocessing engine. Supported players include Winamp, Windows Media Player (9 or later), musicmatch, Sonique, Foobar2000, JetAudio, XMMS. It is ported to Windows and Linux platforms. Unlike the OSS, it is shareware.
4Front OSS3D was later renamed to Joesoft Hear. [16]
OSS both as API and as software has been criticized by some developers, such as Paul Davis (of JACK Audio Connection Kit) and Lennart Poettering (of competing PulseAudio). [17] [18] Most of these criticisms were either specific to the Linux implementation and not to the OSS API itself, or have been addressed in OSS version 4.[ citation needed ]
In computing, a device driver is a computer program that operates or controls a particular type of device that is attached to a computer or automaton. A driver provides a software interface to hardware devices, enabling operating systems and other computer programs to access hardware functions without needing to know precise details about the hardware being used.
Advanced Linux Sound Architecture (ALSA) is a software framework and part of the Linux kernel that provides an application programming interface (API) for sound card device drivers.
JACK Audio Connection Kit is a professional sound server API and pair of daemon implementations to provide real-time, low-latency connections for both audio and MIDI data between applications. JACK was developed by a community of open-source developers led by Paul Davis and has been a key piece of infrastructure and the de facto standard for professional audio software on Linux since its inception in 2002. The server is free software, licensed under GPL-2.0-or-later, while the library is licensed under LGPL-2.1-or-later.
In Unix-like operating systems, /dev/random and /dev/urandom are special files that serve as cryptographically secure pseudorandom number generators (CSPRNGs). They allow access to a CSPRNG that is seeded with entropy from environmental noise, collected from device drivers and other sources. /dev/random typically blocked if there was less entropy available than requested; more recently it usually blocks at startup until sufficient entropy has been gathered, then unblocks permanently. The /dev/urandom device typically was never a blocking device, even if the pseudorandom number generator seed was not fully initialized with entropy since boot. Not all operating systems implement the same methods for /dev/random and /dev/urandom.
A sound server is software that manages the use of and access to audio devices. It commonly runs as a background process.
In computing, ioctl is a system call for device-specific input/output operations and other operations which cannot be expressed by regular file semantics. It takes a parameter specifying a request code; the effect of a call depends completely on the request code. Request codes are often device-specific. For instance, a CD-ROM device driver which can instruct a physical device to eject a disc would provide an ioctl request code to do so. Device-independent request codes are sometimes used to give userspace access to kernel functions which are only used by core system software or still under development.
Netlink is a socket family used for inter-process communication (IPC) between both the kernel and userspace processes, and between different userspace processes, in a way similar to the Unix domain sockets available on certain Unix-like operating systems, including its original incarnation as a Linux kernel interface, as well as in the form of a later implementation on FreeBSD. Similarly to the Unix domain sockets, and unlike INET sockets, Netlink communication cannot traverse host boundaries. However, while the Unix domain sockets use the file system namespace, Netlink sockets are usually addressed by process identifiers (PIDs).
In Unix-like operating systems, a loop device, vnd, or lofi is a pseudo-device that makes a computer file accessible as a block device.
PulseAudio is a network-capable sound server program distributed via the freedesktop.org project. It runs mainly on Linux, including Windows Subsystem for Linux on Microsoft Windows and Termux on Android; various BSD distributions such as FreeBSD, OpenBSD, and macOS; as well as Illumos distributions and the Solaris operating system. It serves as a middleware in between applications and hardware and handles raw PCM audio streams.
Ubuntu Studio is a recognized flavor of the Ubuntu Linux distribution, which is geared to general multimedia production. The original version, based on Ubuntu 7.04, was released on 10 May 2007.
In computing, entropy is the randomness collected by an operating system or application for use in cryptography or other uses that require random data. This randomness is often collected from hardware sources, either pre-existing ones such as mouse movements or specially provided randomness generators. A lack of entropy can have a negative impact on performance and security.
libusb is a library that provides applications with access for controlling data transfer to and from USB devices on Unix and non-Unix systems, without the need for kernel-mode drivers.
ptrace is a system call found in Unix and several Unix-like operating systems. By using ptrace one process can control another, enabling the controller to inspect and manipulate the internal state of its target. ptrace is used by debuggers and other code-analysis tools, mostly as aids to software development.
systemd is a software suite that provides an array of system components for Linux operating systems. The main aim is to unify service configuration and behavior across Linux distributions. Its primary component is a "system and service manager" – an init system used to bootstrap user space and manage user processes. It also provides replacements for various daemons and utilities, including device management, login management, network connection management, and event logging. The name systemd adheres to the Unix convention of naming daemons by appending the letter d. It also plays on the term "System D", which refers to a person's ability to adapt quickly and improvise to solve problems.
Lennart Poettering is a German software engineer working for Microsoft and the original author of PulseAudio, Avahi and systemd.
WildMIDI is a free open-source software synthesizer which converts MIDI note data into an audio signal using GUS sound patches without need for a GUS patch-compatible soundcard. WildMIDI, whose aim is to be as small as possible and easily portable, started in December 2001, can act as a virtual MIDI device, capable of receiving MIDI data from any program and transforming it into audio on-the-fly. It is the standard MIDI renderer for the GStreamer framework.
Entropy-supplying system calls are system calls in Unix-like operating system kernels through which processes can obtain entropic or random data. The first of these was getentropy, introduced to the OpenBSD operating system in release 5.6, as a refactoring of the sysctl(3) KERN_ARND approach used since 1997. Linux offers a very similar system call, getrandom, which was based on getentropy. It was first available in Linux 3.17, released in October 2014. In July 2015, Solaris introduced slightly modified versions of getentropy and getrandom. In August 2015, FreeBSD introduced the read_random system call for obtaining random data from the kernel.
The envsys framework is a kernel-level hardware monitoring sensors framework in NetBSD. As of 4 March 2019, the framework is used by close to 85 device drivers to export various environmental monitoring sensors, as evidenced by references of the sysmon_envsys_register symbol within the sys path of NetBSD; with temperature sensors, ENVSYS_STEMP, being the most likely type to be exported by any given driver. Sensors are registered with the kernel through sysmon_envsys(9) API. Consumption and monitoring of sensors from the userland is performed with the help of envstat utility through proplib(3) through ioctl(2) against the /dev/sysmon pseudo-device file, the powerd power management daemon that responds to kernel events by running scripts from /etc/powerd/scripts/, as well as third-party tools like symon and GKrellM from pkgsrc.
The bio(4) pseudo-device driver and the bioctl(8) utility implement a generic RAID volume management interface in OpenBSD and NetBSD. The idea behind this software is similar to ifconfig, where a single utility from the operating system can be used to control any RAID controller using a generic interface, instead of having to rely on many proprietary and custom RAID management utilities specific for each given hardware RAID manufacturer. Features include monitoring of the health status of the arrays, controlling identification through blinking the LEDs and managing of sound alarms, and specifying hot spare disks. Additionally, the softraid configuration in OpenBSD is delegated to bioctl as well; whereas the initial creation of volumes and configuration of hardware RAID is left to card BIOS as non-essential after the operating system has already been booted. Interfacing between the kernel and userland is performed through the ioctl system call through the /dev/bio pseudo-device.
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