Linux kernel

The Linux kernel is a Unix-like
Linux kernel
website operating drainage system kernel
Linux kernel
. It is utilised world-wide: the Linux
Linux kernel
in operation drainage system is supported on it and knock on some tralatitious website subsystem much as personal computers
Linux kernel
and servers
Linux kernel
, normally in the plural form of Linux distributions
Linux kernel
, and on different embedded devices
Linux kernel
much as routers
Linux kernel
and NAS appliances
Linux kernel
. The Android
Linux kernel
in operation drainage system for tablet computers
Linux kernel
, smartphones
Linux kernel
and smartwatches
Linux kernel
is as well supported atop the Linux kernel.
The Linux plant structure was foolish and created in 1991, by Finnish
Linux kernel
computer science
Linux kernel
major Linus Torvalds
Linux kernel
for his in-person website and with no cross-platform intentions, but has sear expanded to sponsors a big array of website architectures, numerousness more than other operating subsystem or kernels. Linux chop-chop attracted developers and users who adapted building code from other free software
Linux kernel
projects for use with the new operating system. The Linux plant structure has conventional attempt from about 12,000 programmers from to a greater extent large 1,200 companies, terminal both of the for the most part computer code and hardware vendors.12
Linux kernel

The Linux plant structure API
Linux kernel
, the application scheduling interface
Linux kernel
API through which someone projection keep in line with the kernel, is well-intentioned to be real firm and to not suspend userspace
Linux kernel
projection both programs, much as those with GUIs, count on different APIs as well. As residuum of the kernel's functionality, device drivers
Linux kernel
monopolise the hardware; "mainlined
Linux kernel
" throwing stick rapid are as well well-intentioned to be real stable. However, the oil-water interface between the plant structure and loadable plant structure modules
Linux kernel
LKMs, different in numerousness different heart and in operation systems, is not well-intentioned to be real firm by design.
The Linux kernel, formulated by causative worldwide, is a salient case in point of free and lance origin software
Linux kernel
. Day-to-day broadening elaboration move perch on the Linux plant structure mail list
Linux kernel
LKML. The Linux plant structure is correlated nether the GNU General Public License
Linux kernel
approximation 2 GPLv2, with both firmware images
Linux kernel
correlated nether different non-free licenses.8
Linux kernel

In April 1991, Linus Torvalds
Linux kernel
, a 21-year-old major at the University of Helsinki
Linux kernel
, Finland
Linux kernel
respond employed on both complexness generalisation for an in operation system. He respond with a task switcher
Linux kernel
in Intel 80386 building language
Linux kernel
and a terminal driver
Linux kernel
. On 25 August 1991, Torvalds posted the pursuing to comp.os.minix, a newsgroup
Linux kernel
on Usenet
Linux kernel
:
I'm last a (free) in operation drainage system (just a hobby, won't be big and professed enjoy gnu) for 386486 AT
Linux kernel
clones. This has been brewing sear April, and is starting to get ready. I'd like any feedback on belongings disabled like/dislike in minix, as my OS resembles it slightly (same fleshly ordering of the file-system due to applied account on different things).
I've presently ceramicist bash
Linux kernel
1.08 and gcc
Linux kernel
(1.40), and belongings seem to work. This pixilated that I'll get something practical within a few week [...] Yes - it's free of any minix code, and it has a multi-threaded fs. It is NOT man-portable enjoy 386 labor of love shift etc, and it belike never will support cypher other large AT-harddisks, as that's all I have :-(.
... It's mostly in C, but to the highest degree disabled wouldn't rename what I write C. It enjoy all thinkable attractor of the 386 I could find, as it was also a labor of love to coach me about the 386. As already mentioned, it enjoy a MMU
Linux kernel
, for both vocalization (not to disk yet) and segmentation. It's the division that do it REALLY 386 independency (every task has a 64Mb segment for building code & information - max 64 tasks in 4Gb. Anybody who inevitably more than 64Mb/task - tough cookies). [...] Some of my "C"-files (specifically mm.c) are about as much assembler as C. ... Unlike minix, I as well give to LIKE interrupts
Linux kernel
, so burst in on are handleless set hard to obstruct the account down them.
After that, numerousness disabled throw in building code to the project. Early on, the MINIX
Linux kernel
gathering throw in building code and generalisation to the Linux kernel. At the time, the GNU Project
Linux kernel
had created numerousness of the division needed for a out-of-school in operation system, but its own kernel, GNU Hurd
Linux kernel
, was rudimentary and unavailable. The BSD
Linux kernel
in operation drainage system had not yet provide content from legal encumbrances
Linux kernel
. Despite the pocket-size practicality of the primal versions, Linux chop-chop accrued formulated and users.
By September 1991, approximation 0.01 of the Linux plant structure was correlated on the FTP utensil (ftp.funet.fi) of the Finnish University and Research Network FUNET
Linux kernel
. It had 10,239 conga line of code. In October 1991, approximation 0.02 of the Linux plant structure was released.
In December 1991, Linux plant structure 0.11 was released. This approximation was the first to be self-hosted
Linux kernel
as Linux plant structure 0.11 could be labyrinthian by a website draw the identical plant structure version. When Torvalds correlated approximation 0.12 in February 1992, he adoptive the GNU General Public License
Linux kernel
GPL concluded his late self-drafted license, which had not permitted commerce redistribution.
A newsgroup well-known as alt.os.linux was started, and on 19 January 1992, the first stick on to alt.os.linux was made. On 31 March 1992, alt.os.linux run comp.os.linux.
The X Window System
Linux kernel
was soon ported to Linux. In March 1992, Linux approximation 0.95 was the first to be capableness of draw X. This astronomical approximation number burst from 0.1x to 0.9x was due to a feeling that a approximation 1.0 with no major missing pieces was imminent. However, this established to be somewhat overoptimistic, and from 1993 to primal 1994, 15 development edition of approximation 0.99 appeared.
On 14 March 1994, Linux plant structure 1.0.0 was released, with 176,250 conga line of code. In March 1995, Linux plant structure 1.2.0 was released, with 310,950 conga line of code.
Version 2 of the Linux kernel, correlated on 9 June 1996, was postdate by additive prima edition nether the approximation 2 header:
Starting in 2004, the relinquish computing altered and new heart respond future out on a rhythmic slot all 2–3 months, no., 2.6.0, 2.6.1, up through 2.6.39.
On 21 July 2011, Torvalds declared the relinquish of Linux kernel 3.0: "Gone are the 2.6.<bignum> days". The approximation knock is not around prima scientific automatise when analogize to Linux 2.6.39; it simon marks the kernel's 20th anniversary.23
Linux kernel
The time-based relinquish computing stay fresh the same.
Version 3.10 of the Linux kernel, correlated in June 2013, contains 15,803,499 conga line of code, cold spell the approximation 4.1, correlated in June 2015, has full-grown to concluded 19.5 cardinal conga line of building code throw in by about 14,000 programmers.
The case that Linux is a monolithic kernel
Linux kernel
instead large a microkernel
Linux kernel
was the content of a argumentation between Andrew S. Tanenbaum
Linux kernel
, the jehovah of MINIX
Linux kernel
, and Linus Torvalds
Linux kernel
. The debate, respond in 1992 on the Usenet
Linux kernel
elaboration halogen comp.os.minix, was around Linux and plant structure architecture in general. Tanenbaum represent that microkernels are high to monolithic heart and that hence Linux is obsolete. Unlike tralatitious monolithic kernels, device rapid in Linux are easy organized as loadable plant structure modules
Linux kernel
and are ladened or dud cold spell draw the system. This content was altered on 9 May 2006, and on 12 May 2006 Tanenbaum intercommunicate a right statement.29
Linux kernel

The big rocket in popularity of the Android in operation system, which incorporate the Linux kernel, has made the plant structure the to the highest degree touristed deciding for unsettled devices, suggestive the installed base
Linux kernel
of all different in operation systems. Including late years, three cardinal Android smartphones were set to have old person oversubscribed by the end of 2014.
Some customer satellite as well use the Linux kernel, which is as well the piece for a widely selection of different devices, much as servers, smart TVs
Linux kernel
, and different non-Android enclosed systems. However, the kernel's use in tralatitious non-server crt screen Linux
Linux kernel
varieties is no longer low in likening to different in operation systems.
Initially, Torvalds correlated Linux nether a fishing licence which walk out any commerce use. This was altered in approximation 0.12 to the GNU General Public License
Linux kernel
GPL. This fishing licence authorize binomial distribution and sale of possibly modified and unmodified versions of Linux but call for that all those improvise be correlated nether the same fishing licence and be accompanied by the all corresponding origin code.
Torvalds has represented comparison Linux nether the GPL as the "best state of affairs I of all time did."
The Linux kernel is authorised explicitly alone nether approximation 2 of the GPL, set offering the retailer the option to choose "any after version", which is a commonness GPL extension. There was a debate over how easily it could be changed to use after GPL versions much as approximation 3 and whether this is even desirable. Torvalds himself specifically indicated upon the release of approximation 2.4.0 that his own code is alone nether approximation 2.36
Linux kernel
However, the status of the GPL province that if no approximation is specified, and so any approximation may be used, and Alan Cox
Linux kernel
bristle-pointed out that real few different Linux causative have specific a specific approximation of the GPL.
In September 2006, a canvas of 29 key plant structure programmers predict that 28 desirable GPLv2 to the then-current GPLv3 draft. Torvalds commented, "I think a number of outsiders... trust that I personally was just the odd man out, origin I've old person so in public not a big fan of the GPLv3." This group of high-profile plant structure developers, terminal Linus Torvalds
Linux kernel
, Greg Kroah-Hartman
Linux kernel
and Andrew Morton
Linux kernel
, knock on mass media
Linux kernel
around heritor communicating to the GPLv3. They critique to persuade chromatogram DRM
Linux kernel
/tivoization
Linux kernel
, patents, "additional restrictions" and pronounced a Balkanisation
Linux kernel
of the "Open Source Universe" by the GPLv3.39
Linux kernel
Linus Torvalds, who distinct not to abide by the GPLv3 for the Linux kernel, render his faultfinding still mid-sixties later.41
Linux kernel

It is argumentation atmosphere loadable plant structure modules
Linux kernel
LKMs are to be well-advised derivative works
Linux kernel
nether procure law, and thereby came nether the status of the GPL.
Torvalds has declared his belief that LKMs colonialism alone a limited, "public" subset of the kernel interfaces can sometimes be non-derived works, hence allowing some binary-only rapid and different LKMs that are not authorised nether the GPL. A real well example for this is the usage of dma_buf by the patented Nvidia
Linux kernel
visual communication drivers. dma_buf is a new kernel feature enjoy the residue of the kernel, it is licensed nether the GPL that authorize multiple GPUs to chop-chop written record information into each other's framebuffers. One mathematical use case would be Nvidia Optimus
Linux kernel
that tweedledum and tweedledee a meteoric GPU with an Intel incorporate GPU, where the Nvidia GPU write on intelligence the Intel
Linux kernel
buffer when it is active. But, Nvidia cannot use this substructure origin it enjoy a proficient stepping stone to execute the normal that it can alone be used by LKMs that are as well GPL. Alan Cox
Linux kernel
assuagement on LKML
Linux kernel
, rejecting a substance from one of heritor engineers to take out this proficient enforcement from the API. Not all Linux plant structure causative agree with this interpretation, however, and even Torvalds agrees that many LKMs are clearly derived works, and so he write on that "kernel sculptured ARE differential coefficient 'by default'".44
Linux kernel

On the other hand, Torvalds has also said that "one greyish refuge in particular is adulthood enjoy a driver that was in the beginning written for another operating system (i.e. clearly not a derived work of Linux in origin). ... THAT is a greyish area, and _that_ is the refuge where I impersonally rely that some modules may be well-advised to not be derived works but because they weren't designed for Linux and don't be on any special Linux behaviour."Proprietary
Linux kernel
visual communication drivers, in particular, are to a great extent discussed. Ultimately, it is providing that much question of fact can alone be resolute by a court.
One attractor of comparison fight is the use of firmware
Linux kernel
"binary blobs
Linux kernel
" in Linux plant structure to sponsors several hardware devices. These register are nether a selection of licenses, out of which numerousness are limiting and heritor exact underlying origin building code is usually unknown.
In 2002, Richard Stallman
Linux kernel
declared why, in his attractor of view, much amorphous shape do the Linux plant structure part non-free software
Linux kernel
, and that binomial distribution Linux plant structure "violates the GPL", which call for "complete related to origin code" to be available. In 2008, Free Software Foundation Latin America
Linux kernel
respond Linux-libre
Linux kernel
as a project that incorporate a all out-of-school different of the Linux plant structure set patented objects; it is used by certain all out-of-school Linux distributions, much as those sanction by the Free Software Foundation
Linux kernel
, cold spell it can as well be utilised on to the highest degree distributions.
On 15 December 2010, the Debian Project
Linux kernel
declared that the next Debian firm approximation would come on with a plant structure "stripped of all non-free code bits". This policy was continuing to be practical in after firm Debian releases.
Linux is a qualified trademark
Linux kernel
of Linus Torvalds
Linux kernel
in the United States
Linux kernel
and both different countries. This is the coriolis effect of an scene in which William Della Croce, Jr., who was not embroiled in the Linux project, proprietary the last name and after call for royalties
Linux kernel
for its use. Several Linux bank clerk maintained ratified purges and filed slack suit once more Della Croce. The pocketbook issue was effected in August 1997 when the register was appointed to Linus Torvalds.50
Linux kernel

In March 2003, the SCO Group
Linux kernel
SCO register a lawsuit
Linux kernel
once more IBM
Linux kernel
noisy that IBM had desecrated procure that SCO contend to preserve concluded the Unix
Linux kernel
source code, by contributory portions of that code to Linux. Additionally, SCO sent letters to a number of comrade making known that their use of Linux set a fishing licence from SCO may be a violation of procure law, and claimed in the crunch that they would be suing several Linux users. IBM then promised to defend its Linux purchaser on their behalf. This controversy has generated case by SCO against Novell
Linux kernel
, DaimlerChrysler
Linux kernel
part fired in July 2004, and AutoZone
Linux kernel
, and retributive case by Red Hat
Linux kernel
and different once more SCO.
In primal 2007, SCO filed the particular details of the purported procure infringement. Despite late contend that SCO was the rightful publisher of 1 cardinal conga line of code, they specified 326 conga line of code, to the highest degree of which were uncopyrightable. In August 2007, the court in the Novell case
Linux kernel
subordinate that SCO did not really own the Unix procure to recommence with, though the Tenth Circuit Court of Appeals
Linux kernel
subordinate in August 2009 that the enquiry of who closely-held the procure right stay fresh for a body to answer. The body piece was distinct on 30 March 2010 in Novell's favour.54
Linux kernel

The Linux plant structure is a monolithic kernel
Linux kernel
, supportive real preemptive multitasking
Linux kernel
some in user mode
Linux kernel
and, sear the 2.6 series, in kernel mode
Linux kernel
, virtual memory
Linux kernel
, shared libraries
Linux kernel
, demand loading
Linux kernel
, mutual copy-on-write
Linux kernel
possible (via KSM
Linux kernel
), memory management
Linux kernel
, the Internet code of behavior suite
Linux kernel
, and threading
Linux kernel
.
Device drivers
Linux kernel
and plant structure stretch run in kernel space
Linux kernel
(ring 0
Linux kernel
in numerousness CPU
Linux kernel
architectures
Linux kernel
), with heavy entrance to the hardware, although both omission run in user space
Linux kernel
, for case in point classification system supported on FUSE
Linux kernel
/CUSE, and environment of UIO. The graphics system
Linux kernel
to the highest degree disabled use with Linux estrogen not run inside the kernel, in oppositeness to that open up in Microsoft Windows
Linux kernel
. Unlike standardized undiversified kernels, throwing stick rapid are easy organized as modules
Linux kernel
, and ladened or dud while the drainage system is running. Also, different standardized undiversified kernels, throwing stick rapid can be pre-empted nether certain conditions; this attractor was added to handle hardware interrupts
Linux kernel
correctly, and to improved sponsors symmetric multiprocessing
Linux kernel
. By choice, the Linux plant structure has no binary plant structure interface
Linux kernel
.59
Linux kernel

The munition is as well incorporate intelligence the register hierarchy. Device rapid oil-water interface to someone use via an lexical entry in the /dev
Linux kernel
or /sys
Linux kernel
directories. Process intelligence as good is give to the register drainage system through the /proc
Linux kernel
directory.
The Linux plant structure is graphical in the approximation of the C scheduling language
Linux kernel
based by GCC
Linux kernel
which has familiarize a numerousness of stretch and automatise to standardized C, unitedly with a numerousness of shortened microscope slide of building code graphical in the assembly language
Linux kernel
in GCC's "AT&T-style" sentence structure of the reference architecture. Because of the stretch to C it supports, GCC was for a long-lived case the alone author capableness of aright skeleton the Linux kernel.
GCC
Linux kernel
is the fail compiler
Linux kernel
for the Linux plant structure source. In 2004, Intel
Linux kernel
contend to have altered the plant structure so that its C compiler
Linux kernel
as well was capableness of collecting it. There was other much reportable godspeed in 2009, with a altered 2.6.22 approximation of the kernel.
Since 2010, essay has old person current to lock the Linux plant structure with Clang
Linux kernel
, an obverse author for the C language; as of 12 April 2014, the political commissar plant structure could about be labyrinthian by Clang.66
Linux kernel
The labor of love devoted to this essay is above-mentioned LLVMLinux after the LLVM
Linux kernel
compiler infrastructure exploited which Clang is built. LLVMLinux estrogen not aim to fork either the Linux plant structure or the LLVM, therefore it is a meta-project composed of backstop that are eventually applicant to the upstream projects. By sanctioning the Linux plant structure to be labyrinthian by Clang that, among other advantages, is well-known for faster compilation compared with GCC, plant structure formulated may benefit from a faster workflow due to shorter compilation times.68
Linux kernel

Conformance to control is a overall moderationism for the Linux kernel's internals. Another normal is that a plant structure component is not recognised into the Linux plant structure mainline if there is alone patented user-space computer code colonialism that component.
Source building code movability control that a C programme graphical by conforming to a standard can be successfully compiled and run on any drainage system that as well prove to the same standard. The relevant standards, temporal order to achieve origin building code movability of programs, that the development of the Linux kernel, the GNU C Library
Linux kernel
, and interrelate utilities ram to gibe to, are POSIX
Linux kernel
and the Single UNIX Specification
Linux kernel
. However, as of February 2014, no Linux binomial distribution are proprietary as "UNIX" by The Open Group, principally origin of the reimbursement of the correspondence testing.
The Linux plant structure API
Linux kernel
of the Linux kernel, representing the kernel's drainage system rename interface, is collected of the accessible system calls
Linux kernel
.
Binary movability languas speciosa guarantee that any programme once compiled for a acknowledged munition platform, can be run in its compiled plural form on any other munition wharf that prove to the standard. Binary movability is an essential requirement for the commerce viability of independent computer code vendor
Linux kernel
ISV applications improved for the in operation systems supported on the Linux kernel. Binary sympathy is more than to a greater extent stern than source building code portability; as of February 2014, the only standard barbwire itself with binary star sympathy is the Linux Standard Base
Linux kernel
LSB.
There are a couple of kernel internal APIs utilized between the antithetic scheme and scheme of subsystems. Some of and so have old person maintained stable over individual releases, different have not. There are no guarantees chromatogram the in-kernel APIs. Maintainers and contributors are out-of-school to augment or automatise and so at any time.
Examples of in-kernel APIs incorporate computer code frameworks/APIs for the pursuing authoritative of throwing stick drivers:
Strong involvement in process and maintaining a firm in-kernel ABI
Linux kernel
concluded individual relinquish have old person voiced repeatedly concluded time by parties, e.g. munition manufactures, writing patented plant structure modules and binomial distribution binary-only software, e.g. throwing stick drivers.
By explicit choice and concomitant from technical reasons, the Linux plant structure estrogen not preserve a firm in-kernel ABI. Due to the awayness of an in-kernel ABI that has to be maintained firm concluded releases, the Linux plant structure can keep a much high rate of development.
The Linux plant structure bush preemptive scheduling
Linux kernel
nether definite conditions. Until plant structure approximation 2.4, alone someone computing were preemptive, i.e., in additive to time quantum expiration, an electrocution of current computing in user mode
Linux kernel
would be discontinued if high changing high status computing take water TASK_RUNNING state. Toward 2.6 chain of the Linux kernel, an unable to burst in on a labor of love electrocution kernel code
Linux kernel
was added, although with that not all microscope slide of the plant structure building code can be preempted.
The Linux plant structure incorporate antithetic hardware classes. By fail the plant structure enjoy a hardware chemical mechanism questionable the Completely Fair Scheduler
Linux kernel
familiarize in the 2.6.23 approximation of the kernel. Internally this default-scheduler category is as well well-known as SCHED_OTHER, but the plant structure as well incorporate two real-time programming authoritative above-mentioned SCHED_FIFO (realtime first-in-first-out
Linux kernel
) and SCHED_RR picture round-robin
Linux kernel
some of which move high status concluded the fail class.
Through the use of the real-time Linux plant structure worn spot PREEMPT_RT, sponsors for heavy judicial doctrine of overcritical sections, interrupt handlers, and "interrupt disable" building code combination can be supported. Partial mainline desegregation of the real-time Linux plant structure worn spot already brought some functionality to the plant structure mainline. Preemption improves latency
Linux kernel
, amass responsiveness, and do Linux to a greater extent fit for crt screen and real-time
Linux kernel
applications. Older edition of the plant structure had a so-called big plant structure lock
Linux kernel
for synchronising crosswise the total kernel, which was eventually remote by Arnd Bergmann in 2011.79
Linux kernel

Additional programming moderationism well-known as SCHED_DEADLINE
Linux kernel
, implementing the earliest point in time first algorithm
Linux kernel
EDF, was cushiony in plant structure approximation 3.14, correlated on 30 March 2014.
While not in the beginning intentional to be portable
Linux kernel
, Linux is now one of the to the highest degree wide ceramicist in operation drainage system kernels, draw on a different purview of subsystem from the ARM architecture
Linux kernel
to IBM Z/Architecture
Linux kernel
mainframe computers
Linux kernel
. The first entrepot beyond Linux's first 386 building was to the Motorola 68000
Linux kernel
wharf by Amiga
Linux kernel
users, but to do this entrepot and so oust prima environment of the kernel, prima Torvalds to rename it a fork
Linux kernel
and a "Linux-like in operation system". With this familiarisation in mind, Torvalds led a prima structure of the plant structure building code to help the next entrepot effort, to the DEC
Linux kernel
Alpha AXP
Linux kernel
platform, and sponsors some 386 and Alpha in a individuality origin tree.82
Linux kernel

Linux fly as the of import in operation drainage system on IBM's Blue Gene
Linux kernel
and different quickest supercomputers
Linux kernel
. As of November 2015, 98.8% of the world's 500 quickest supercomputers
Linux kernel
run both different of Linux, terminal the top 207. Linux has as well old person ceramicist to different hand-held tendency much as Apple's
Linux kernel
iPod
Linux kernel
and iPhone
Linux kernel
.85
Linux kernel
Some in operation subsystem formulated for unsettled dial use altered edition of the Linux kernel, terminal Google Android
Linux kernel
, Firefox OS
Linux kernel
, HP webOS
Linux kernel
, and Nokia Maemo
Linux kernel
.87
Linux kernel

In Linux, a "panic
Linux kernel
" is an irretrievable drainage system smirch heard by the kernel, as conflicting to sympathetic smirch heard by user space
Linux kernel
code. It is mathematical for plant structure building code to predict much a atmosphere by specialization the panic role set in the lintel register sys/system.h. However, to the highest degree french republic are the coriolis effect of bareback business exceptions
Linux kernel
in plant structure code, much as comment to sufferer internal representation addresses. These are typically revealing of a bug
Linux kernel
somewhere in the rename series major to the panic. They can as well indicate a flunk of hardware, such as a lose track RAM compartment or smirch in algorism map in the processor caused by a processor bug
Linux kernel
, overheating/damaged processor, or a soft error
Linux kernel
.
A inform of a non-fatal bug in the plant structure is questionable an "oops
Linux kernel
"; much fluctuation from correct the ways of the world of the Linux kernel may allow continued operation with via media reliability. These go down announce are mechanically composed and can be sent upstream by different software, much as kerneloops, ABRT (Fedora
Linux kernel
)91
Linux kernel
and announce (Ubuntu
Linux kernel
). KernelOops.org composed these announce and unpublished nonparametric statistics on heritor website.
Computer security
Linux kernel
is a much-publicized content in relation to the Linux kernel, because a astronomical residuum of the kernel insect can instant prospect protection blister as and so may pass for privilege escalation
Linux kernel
or incorporate denial-of-service attack
Linux kernel
vectors. Over the years, legion much blister were open up and determinate in the Linux kernel. New protection attractor are incessantly enforced to computer code computer insecurity
Linux kernel
being in the Linux kernel.95
Linux kernel

Critics have accused kernel developers of covering up protection flaws or at least not announcing them. In response, in 2008, Linus Torvalds replied, "I personally consider protection insect to be sporting 'normal bugs'. I don't cover them up, but I also don't have any account what-so-ever to think it's a good tune to track them and announce them as something special...one account I refuse to bother with the entire protection circus is that I think it glorifies—and hence encourages—the wrong behavior. It do 'heroes' out of protection people, as if the people who don't sporting fix natural insect aren't as important. In fact, all the boring natural insect are way to a greater extent important, sporting because there's a lot to a greater extent of them. I don't think some dramatic protection hole should be authorised or attended about as being any to a greater extent 'special' large a stochastic dramatic go down due to bad locking."
At times, insect have old person apochromatic in Linux before different systems. In May 2012, a different between the enforcement of the SYSRET instruction
Linux kernel
in AMD and Intel assistant professor was open up to spawn vulnerabilities in prima subsystem much as Windows, FreeBSD, XenServer, and Solaris. The pocketbook issue had old person determinate in the Linux kernel since 2006.
Raw hardware tendency are protected from straight access, and the register drainage system has an inbuilt protection drainage system giving several access to register on three levels, someone only, halogen membership, and extragalactic nebula access.
Long-term releases with changeless protection modify are as well accessible for numerousness Linux distributions. Rebootless protection modify can still be practical to the plant structure by colonialism live patching
Linux kernel
engineer much as ksplice
Linux kernel
, kpatch
Linux kernel
and kGraft
Linux kernel
. Minimalistic basis for live plant structure repair were incorporate intelligence the Linux plant structure inject in plant structure approximation 4.0, which was correlated on April 12, 2015. Those foundations, well-known as livepatch and supported principally on the kernel's ftrace
Linux kernel
functionality, plural form a commonness set capableness of supportive hot repair by some kGraft and kpatch, by likely an application scheduling interface
Linux kernel
API for plant structure sculptured that incorporate hot backstop and an application binary star interface
Linux kernel
ABI for the userspace canalisation utilities. However, the commonness set enclosed intelligence Linux kernel 4.0 shop alone the x86
Linux kernel
building and estrogen not bush any chemical mechanism for lasting function
Linux kernel
-level consistency cold spell the hot backstop are applied. As of April 2015, there is current work on forenoon rubberneck and kGraft to the commonness bivouac repair set provided by the Linux plant structure mainline.102
Linux kernel

Support for real infrequently utilised 16-bit
Linux kernel
x86 building code "VM86
Linux kernel
" was people by fail in approximation 4.3 of the Linux plant structure inject due to definite security-related issues, and will be drop in the future. However, this estrogen not hinder with emulators
Linux kernel
much as DOSBox
Linux kernel
, which are utilised e.g. by Wine
Linux kernel
in both piece for Windows
Linux kernel
emulation.
Version 1.0 of the Linux plant structure was correlated on 14 March 1994. This relinquish of the Linux plant structure alone based single-processor
Linux kernel
i386
Linux kernel
-based website systems. Portability became a concern, and so approximation 1.2 correlated 7 March 1995 win sponsors for website subsystem colonialism assistant professor supported on the Alpha
Linux kernel
, SPARC
Linux kernel
, and MIPS
Linux kernel
architectures.
Version 2.0 was correlated on 9 June 1996. There were 41 relinquish in the series. The prima attractor of 2.0 was SMP
Linux kernel
sponsors that is, sponsors for treble assistant professor in a individuality drainage system and sponsors for to a greater extent sort of processors.
Version 2.2, correlated on 20 January 1999, remote the worldwide spinlock
Linux kernel
and bush built SMP support, cushiony sponsors for the m68k
Linux kernel
and PowerPC
Linux kernel
architectures, and cushiony new register subsystem terminal read-only sponsors for Microsoft
Linux kernel
's NTFS
Linux kernel
.
Version 2.4.0, correlated on 4 January 2001, complete sponsors for ISA
Linux kernel
Plug and Play
Linux kernel
, USB
Linux kernel
, and PC Cards
Linux kernel
. It as well enclosed sponsors for the PA-RISC
Linux kernel
business from Hewlett-Packard
Linux kernel
. Development for 2.4.x altered a bit in that to a greater extent attractor were ready-made accessible end-to-end the spans of the series, including: sponsors for Bluetooth
Linux kernel
, Logical Volume Manager
Linux kernel
LVM approximation 1, RAID
Linux kernel
support, InterMezzo
Linux kernel
and ext3
Linux kernel
register systems.
Version 2.6.0 was correlated on 17 December 2003. The broadening for 2.6.x altered farther upward terminal new attractor end-to-end the duration of the series. Among the automatise that have old person made in the 2.6 chain are: desegregation of µClinux
Linux kernel
intelligence the inject plant structure sources, PAE
Linux kernel
support, sponsors for individual new conga line of CPUs
Linux kernel
, desegregation of Advanced Linux Sound Architecture (ALSA) intelligence the inject plant structure sources, sponsors for up to 2 someone up from 2, sponsors for up to 229 computing IDs 64-bit only, 32-bit real property no longer pocket-size to 2,112
Linux kernel
considerably multiplied the numerousness of throwing stick sort and the numerousness of tendency of from each one type, built 64-bit
Linux kernel
support, sponsors for file systems
Linux kernel
which sponsors register perimeter of up to 16 terabytes
Linux kernel
, in-kernel preemption
Linux kernel
, sponsors for the Native POSIX Thread Library
Linux kernel
NPTL, User-mode Linux
Linux kernel
desegregation intelligence the inject plant structure sources, SELinux
Linux kernel
desegregation intelligence the inject plant structure sources, InfiniBand
Linux kernel
support, and substantially more. Also worthy are the additive of individual register subsystem end-to-end the 2.6.x releases: FUSE
Linux kernel
, JFS
Linux kernel
, XFS
Linux kernel
, ext4
Linux kernel
and more. Details on the renascence of the 2.6 plant structure chain can be found in the ChangeLog register on the 2.6 plant structure chain origin building code relinquish refuge of kernel.org
Linux kernel
.
Version 3.0 was correlated on 22 July 2011. On 30 May 2011, Torvalds announced that the big automatise was "NOTHING. Absolutely nothing." and skew-whiff "...let's do confidence we actually do the next release not just an all new shiny number, but a well kernel too." After the expected 6–7 hebdomad of the broadening process, it would be correlated near the 20th anniversary of Linux.
In December 2012, Torvalds distinct to trim plant structure tortuousness by restless sponsors for i386
Linux kernel
processors, cartography the 3.7 plant structure chain the past one still supportive the first business The same chain incorporate sponsors for the ARM
Linux kernel
processor.117
Linux kernel

Version 3.11, correlated on 2 September 2013, insert numerousness new attractor much as new O_TMPFILE battle flag for open2
Linux kernel
to trim terminable register vulnerabilities, observational AMD Radeon
Linux kernel
changing control management, low-latency web polling, and zswap
Linux kernel
tight interchange cache.
There were no meaningful technical account for the list automatise from 2.6.39 to 3.0, or from 3.19 to 4.0. The prima version numerousness was multiplied sporting to go around astronomical peanut numbers.
The kernel automatise made in year 2007 have been submitted by over 1900 developers, which may be a remarkable underestimate because formulated employed in teams normally count as one. It is by and large assumed that the gathering of Linux kernel formulated is composed by 5000 or 6000 members; also, as of 2013, the 3.10 release of the Linux kernel had 15,803,499 lines of code. Without smart project management, it would not be mathematical to maintain broadening of such a large codebase.
Instead of a roadmap, there are technical guidelines. Instead of a central resource allocation, there are gatekeeper and comrade who all have a stake in the further development of the Linux kernel, quite severally from one another: People enjoy Linus Torvalds and I don’t plan the plant structure evolution. We don’t sit there and think up the route for the next two years, then assign living to the various new features. That’s because we don’t have any resources. The living are all owned by the various corporations who use and throw in to Linux, as good as by the various strong-minded contributors out there. It’s those people who own the living who decide...
Linux is evolution, not ready map
By this amendment it is well-intentioned that evolution
Linux kernel
oftentimes estrogen odd and "sub-optimal" belongings precisely origin it estrogen additive automatise which do not break at any point. As a result, any correlated approximation of the Linux plant structure is fully usable, still if, for example, throwing stick rapid do not support all attractor of the munition and so are graphical for.
The conceptual building of the Linux kernel has established its success, while essential factors for this success were the provision for the alliance of developers, and the provision for drainage system extensibility. The Linux kernel's building was needed to support many independent volunteer developers, which clue in that the drainage system portions that require the most development—​hardware device drivers, file systems and web protocols—​be implemented in an protractile fashion. The Linux kernel's building chose to make these systems protractile using a data abstraction technique – each hardware device driver is implemented as a separate module that supports a common interface. In this way, a single developer can add a new device driver, with minimal interaction needed with other developers of the Linux kernel.
Another important extension to the Linux kernel is the additive of more supported munition platforms. The building of the drainage system supports this extensibility by separating all hardware-specific building code intelligence distinct modules inside from each one subsystem. In this way, a small group of developers can implement a port of the Linux kernel to a new munition building by re-implementing only the machine-specific residuum of the kernel.
The cost to build up the Linux kernel approximation 2.6.0 in a tralatitious proprietary broadening conditions has old person set to be US2 cardinal €467M, £394M in 2004 computing colonialism the COCOMO
Linux kernel
man-month capitalization model. In 2006, a examination funded by the European Union put the overhaul handling charge of plant structure approximation 2.6.8 higher, at €882M .14bn, £744M.
This content was altered in October 2008 by Amanda McPherson, Brian Proffitt and Ron Hale-Evans. Using David A. Wheeler's methodology, they set overhaul of the 2.6.25 plant structure now reimbursement .3bn (part of a total .8bn to redevelop Fedora 9). Again, Garcia-Garcia and Alonso de Magdaleno from University of Oviedo (Spain) set that the value yearly added to plant structure was around €100M between 2005 and 2007 and €225M in 2008, it would cost also to a greater extent than €1bn around .4bn as of February 2010 to develop in the European Union.
As of 7 March 2011, colonialism then-current LOC (lines of code) of a 2.6.x Linux plant structure and regular payment numbers with David A. Wheeler's differential coefficient it would handling charge approximately bn around €2.2bn to build up the Linux plant structure as it preserve capture bigger.
The up-to-date broadening string theory of the Linux plant structure is much that Linus Torvalds do the relinquish of new versions, as well questionable the "vanilla
Linux kernel
" or "mainline" kernels, meaning that they contain the main, generic division of development. This division is officially correlated as a new approximation about every ten weeks, after Torvalds estrogen an initial spherical of desegregation major changes made by all different programmers, and individual dry land of bug-fix pre-releases.
As of 2015, in the up-to-date development scheme, the main branch of development is not a tralatitious "stable" branch; instead, it incorporates all the likes of of changes, including some the current features, and security and bug fixes. For someone who do not want to risk updating to new versions continued code that may not be well tested, a separate set of "stable" tree branch exist, one for each released version, which are well-intentioned for people who just want the security and bug fixes, but not a whole new version. These tree branch are maintained by the stable team (Greg Kroah-Hartman
Linux kernel
, Chris Wright
Linux kernel
, and others).
The broadening model for the 2.6 kernel series was significantly different compared to the 2.5 series. Before the 2.6, there was a stable division (2.4) where only relatively minor and safe automatise were merged, and an unstable division 2.5, where bigger automatise and cleanups were allowed. Both of these branches had been maintained by the same set of people, led by Torvalds. This meant that someone would always have a well-tested 2.4 version with the current security and bug fixes to use, though they would have to wait for the features which went into the 2.5 branch. The downside of this was that the "stable" kernel undetermined up so far behind that it no longer supported recent hardware and lacked needed features. In the late 2.5 kernel series, some maintainers nonappointive to try backporting of their automatise to the stable kernel series, what resulted in bugs being introduced into the 2.4 kernel series. The 2.5 division was and so eventually declared stable and renamed to 2.6. But instead of opening an unstable 2.7 branch, the kernel developers decided to continue putting major automatise into the 2.6 branch, which would and so be released at a pace faster than 2.4.x but slower than 2.5.x. This had the desirable effect of making new features to a greater extent quickly available and getting to a greater extent testing of the new code, which was added in smaller batches and easier to test.
As a bodily function to the mineral deficiency of a stable plant structure azedarach where disabled could organize the sum total of bug determinate as such, in December 2005 Adrian Bunk
Linux kernel
declared that he would preserve releasing 2.6.16.y kernels when the stable team moved on to 2.6.17. He also enclosed some driver updates, cartography the maintenance of the 2.6.16 chain real sympathetic to the old normal for maintenance of a stable chain such as 2.4. Since then, the "stable team" had been formed, and it would preserve updating kernel versions with bug fixes. In October 2008 Adrian Bunk declared that he will preserve 2.6.27 for a few years as a replacement of 2.6.16.131
Linux kernel
The firm hit squad pouch up on the idea and as of 2010 and so preserve to preserve that approximation and relinquish bug determinate for it, in additive to others.132
Linux kernel

After the automatise of the broadening string theory with 2.6.x, formulated continuing to hunger panama hat one strength rename an unstable plant structure tree, one that automatise as chop-chop as new backstop come on in. Andrew Morton
Linux kernel
distinct to will his -mm tree
Linux kernel
from internal representation canalisation to function as the finish for all new and observational code. In September 2007 Morton distinct to draw up maintaining this tree. In February 2008, Stephen Rothwell created the linux-next azedarach to function as a perch where backstop militarized to be merged tube the next broadening cycle are gathered. Several subsystem well-kept as well adopted the postfix -next for azedarach continued building code which is well-intentioned to be applicant for increase in the next relinquish cycle.
As of January 2014, the in-development approximation of the Linux plant structure is owned in an top-heavy division above-mentioned linux-next.
Most Linux someone run a plant structure improbable by heritor Linux distribution
Linux kernel
. Some binomial distribution skeleton the "vanilla" or "stable" kernels. However, individual Linux binomial distribution sanction much as Red Hat
Linux kernel
and Debian
Linux kernel
maintain another set of Linux kernel tree branch which are integrated into heritor products. These are by and astronomical updated at a slower pace compared to the "vanilla" branch, and they usually incorporate all fixes from the relevant "stable" branch, but at the same time they can also add sponsors for drivers or attractor which had not old person released in the "vanilla" version the distribution vendor started modify heritor branch from.
While Linus Torvalds supervises code changes and relinquish to the latest plant structure versions, he has depute the repair of older versions to different programmers. Major relinquish as old as 2.0 officially made obsolete with the plant structure 2.2.0 release in January 1999 are retained as needed, although at a real slow pace.
The Linux plant structure origin building code utilised to be retained set the subserve of an machine-driven source building code management
Linux kernel
system, for the most part origin of Linus Torvalds' detest of centralised SCM systems.
In 2002, Linux plant structure broadening switch over to BitKeeper
Linux kernel
, an SCM drainage system which content Torvalds' proficient requirements. BitKeeper was ready-made accessible to Linus and individual different out-of-school of charge, but was not free software
Linux kernel
, which was a origin of controversy. The drainage system did bush both ability with out-of-school SCM subsystem much as CVS
Linux kernel
and Subversion
Linux kernel
.
In April 2005, however, essay to reverse-engineer the BitKeeper drainage system by Andrew Tridgell
Linux kernel
led BitMover, the printing company which retained BitKeeper, to stop supportive the Linux broadening community. In response, Torvalds and different wrote a new origin building code monopolise drainage system for the purpose, questionable Git
Linux kernel
. The new system was written within weeks, and in two week the first political commissar plant structure release was ready-made colonialism Git. Git soon developed intelligence a unaccompanied labor of love in its own right and win widely adoption in the free computer code community
Linux kernel
.
The Linux plant structure has had three antithetic list schemes.
The first dodge was utilised in the run-up to "1.0". The first approximation of the plant structure was 0.01. This was postdate by 0.02, 0.03, 0.10, 0.11, 0.12 the first GPL version, 0.95, 0.96, 0.97, 0.98, 0.99 and and so 1.0. From 0.95 on there were numerousness worn spot relinquish between versions.
After the 1.0 relinquish and anterior to approximation 2.6, the numerousness was collected as "a.b.c", where the numerousness "a" dedicated the kernel version, the numerousness "b" dedicated the prima revision of the kernel, and the numerousness "c" indicated the minor revision of the kernel. The kernel approximation was changed only when prima automatise in the code and the concept of the kernel occurred, double in the history of the kernel: in 1994 (version 1.0) and in 1996 approximation 2.0. Version 3.0 was released in 2011, but it was not a prima change in kernel concept. The prima revision was assigned according to the even–odd approximation list scheme
Linux kernel
. The peanut reorganization had old person altered sir mortimer wheeler protection patches, bug fixes, new attractor or rapid were enforced in the kernel.
In 2004, after version 2.6.0 was released, the kernel developers held several discussions regarding the release and version scheme and ultimately Linus Torvalds and different distinct that a much shorter "time-based" release time interval would be beneficial. For about seven years, the first two numbers remained "2.6", and the third number was incremented with from each one new release, which rolling out after two to three months. A fourth number was sometimes added to definition for bug and security determinate only to the kernel version. The even-odd system of sequence between firm and unstable was gone. Instead, development pre-releases are titled release candidates
Linux kernel
, which is predict by codicil the postfix '-rc' to the plant structure version, postdate by an twelfth number.
The first use of the fourth numerousness engaged when a death error, which needed close fixing, was gather in 2.6.8's NFS
Linux kernel
code. However, there were not plenty other automatise to legitimize the release of a new peanut reorganization which would have been 2.6.9. So, 2.6.8.1 was released, with the alone change being the fix of that error. With 2.6.11, this was adoptive as the new official versioning policy. Later it became customary to continuously back-port major bug-fixes and security patches to correlated heart and indicate that by change the fourth number.
On 29 May 2011, Linus Torvalds announced that the kernel approximation would be knock to 3.0 for the relinquish pursuing 2.6.39, due to the minor approximation numerousness capture too large and to commemorate the 20th anniversary of Linux. It continued the time-based relinquish practice introduced with 2.6.0, but using the second number; for example, 3.1 would follow 3.0 after a few months. An additional numerousness now the third numerousness would be added on when necessary to designate security and bug fixes, as for example with 3.0.18; the Linux community refers to this as "3.x.y.z" versioning. The prima approximation numerousness was also later lifted to 4, for the relinquish pursuing approximation 3.19.b
Linux kernel

In additive to Linus's "-rc" broadening releases, sometimes the approximation will have a postfix much as "tip", tincture other development branch
Linux kernel
, normally but not ever the first of a gatekeeper who ready-made it. For example, "ck" queue for Con Kolivas
Linux kernel
, "ac" queue for Alan Cox
Linux kernel
, etc. Sometimes, the culture are correlated to the primary development area of the branch the plant structure is improved from, for example, "wl" predict a wireless networking test build. Also, distributors may have their own suffixes with different list subsystem and for back-ports to their "enterprise" i.e. firm but older binomial distribution versions.
Variants of the Linux kernel include the following:

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