Long-term support (LTS) is term used to describe special versions or editions of software designed to be supported for a longer than normal period. It is particularly applicable to open-source software projects.
It is a product lifecycle management policy for computer software, that applies the tenets of reliability engineering to the software development process and software release life cycle. Long-term support extends the period of software maintenance; it also alters the type and frequency of software updates (patches) to reduce the risk, expense, and disruption of software deployment, while promoting the dependability of the software. It does not, however, imply technical support.
At the beginning of a long-term support period, the software developers impose a feature freeze: They make patches to correct software bugs and vulnerabilities, but do not introduce new features that may cause regression. The software maintainer either distributes patches individually, or packages them in maintenance releases, point releases, or service packs. At the conclusion of the support period, the product reaches end-of-life.
The term long-term-support is usually reserved for special versions or editions of software that otherwise has a much shorter release life cycle. Typically, a publisher of LTS software maintains it for at least two years.
The need for long-term support
The traditional software lifecycle in many open source projects is release early, release often, or a regular time-based release schedule. In either case, each new release includes both fixes for security vulnerabilities and new functionality.
Large organisations, or users with mission critical projects, need the security fixes but would often prefer to retain the same base version for an extended period without any new or changed functionality. Their concern is, that as software developers add new features they can accidentally introduce new bugs or break old functionality. While in theory they could backport just the security fixes from each new release to their deployed version, in practise this would often be prohibitively difficult or costly.
Even without the added risks, for these types of users, new functionality is also often expensive. Updating a web application with a sensitive configuration, for example, may require the cooperation of many people: Developers for retrofitting; a database administrator for database schema changes; software testers for regression testing; a project manager for scheduling, liaising, and facilitating; a system administrator or release manager for software deployment oversight; and IT operations personnel for backups, installation, and disaster recovery.
LTS versions of a software package typically address these concerns by releasing only security-related updates for the LTS version - such that installing them should always be less risky than not installing them.
Software with separate LTS versions
This table only lists those have a specific LTS version in addition to a normal release cycle. Many projects, such as CentOS, provide a long period of support for every release.
|Software||Software type||Date of first LTS release||LTS period||STS period||Notes|
|Ubuntu||Linux distribution||1 June 2006
|5 years||6 months1||A new LTS version is released every two years. From 2006 through 2011, LTS support for the desktop was for approximately two years, and for servers five, but LTS versions are now supported for five years on either.|
|2 years, 3 months||7 months||Since Joomla! is a web application, long-term support also implies support for legacy web browsers.|
|Linux Mint||Linux distribution||8 June 2008||5 years||6 months||At version 13 the LTS period increased from three years to five, since Linux Mint derives from Ubuntu.|
|Linux kernel||Kernel||11 October 2008
|2–3 years||Varies||Linux kernel v2.6.16 and v2.6.27, were unofficially supported in LTS fashion before a 2011 working group in the Linux Foundation started a formal Long Term Support Initiative.|
|3 years (min.)||Varies||TYPO3 is a web application stewarded by the TYPO3 Association.|
|Mozilla Firefox||Web browser||31 January 2012
|1 year||6 weeks||Mozilla's LTS term is "Extended Support Release" (ESR) (see Firefox#Extended Support Release).|
- 1.^ The support period for Ubuntu's parent distribution, Debian, is one year, with a point release every two months.
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