As of OTP release 17, the OTP release number corresponds to the major part of the OTP version. The OTP version as a concept was introduced in OTP 17. The version scheme used is described in more detail below.
OTP of a specific version is a set of applications of specific versions. The application versions identified by an OTP version corresponds to application versions that have been tested together by the Erlang/OTP team at Ericsson AB. An OTP system can however be put together with applications from different OTP versions. Such a combination of application versions has not been tested by the Erlang/OTP team. It is therefore always preferred to use OTP applications from one single OTP version.
Release candidates have an -rc<N> suffix. The suffix -rc0 will be used during development up to the first release candidate.
Retrieving Current OTP Version
In an OTP source code tree, the OTP version can be read from the text file <OTP source root>/OTP_VERSION. The absolute path to the file can be constructed by calling filename:join([code:root_dir(), "OTP_VERSION"]).
In an installed OTP development system, the OTP version can be read from the text file <OTP installation root>/releases/<OTP release number>/OTP_VERSION. The absolute path to the file can by constructed by calling filename:join([code:root_dir(), "releases", erlang:system_info(otp_release), "OTP_VERSION"]).
If the version read from the OTP_VERSION file in a development system has a ** suffix, the system has been patched using the otp_patch_apply tool available to licensed customers. In this case, the system consists of application versions from multiple OTP versions. The version preceding the ** suffix corresponds to the OTP version of the base system that has been patched. Note that if a development system is updated by other means than otp_patch_apply, the OTP_VERSION file may identify an incorrect OTP version.
No OTP_VERSION file will be placed in a target system created by OTP tools. This since one easily can create a target system where it is hard to even determine the base OTP version. You may, however, place such a file there yourself if you know the OTP version.
OTP Versions Table
The text file <OTP source root>/otp_versions.table that is part of the source code contains information about all OTP versions from OTP 17.0 up to current OTP version. Each line contains information about application versions that are part of a specific OTP version, and is on the format:
<OtpVersion> : <ChangedAppVersions> # <UnchangedAppVersions> :
<OtpVersion> is on the format OTP-<VSN>, i.e., the same as the git tag used to identify the source. <ChangedAppVersions> and <UnchangedAppVersions> are space separated lists of application versions on the format <application>-<vsn>. <ChangedAppVersions> corresponds to changed applications with new version numbers in this OTP version, and <UnchangedAppVersions> corresponds to unchanged application versions in this OTP version. Both of them might be empty, although not at the same time. If <ChangedAppVersions> is empty, no changes has been made that change the build result of any application. This could for example be a pure bug fix of the build system. The order of lines is undefined. All white space characters in this file are either space (character 32) or line-break (character 10).
Using ordinary UNIX tools like sed and grep one can easily find answers to various questions like:
- Which OTP versions are kernel-3.0 part of?
$ grep ' kernel-3\.0 ' otp_versions.table
- In which OTP version was kernel-3.0 introduced?
$ sed 's/#.*//;/ kernel-3\.0 /!d' otp_versions.table
The above commands give a bit more information than the exact answers, but adequate information when manually searching for answers to these questions.
The format of the otp_versions.table might be subject to changes during the OTP 17 release.
As of OTP 17.0 application versions will use the same version scheme as the OTP version. Application versions part of a release candidate will however not have an -rc<N> suffix as the OTP version. Also note that a major increment in an application version does not necessarily imply a major increment of the OTP version. This depends on whether the major change in the application is considered as a major change for OTP as a whole or not.
Note that the version scheme was changed as of OTP 17.0. This implies that application versions used prior to OTP 17.0 do not adhere to this version scheme. A list of application versions used in OTP 17.0 can be found at the end of this document.
In the normal case, a version will be constructed as <Major>.<Minor>.<Patch> where <Major> is the most significant part. However, more dot separated parts than this may exist. The dot separated parts consists of non-negative integers. If all parts less significant than <Minor> equals 0, they are omitted. The three normal parts <Major>.<Minor>.<Patch> will be changed as follows:
- Increased when major changes, including incompatibilities, have been made.
- Increased when new functionality has been added.
- Increased when pure bug fixes have been made.
When a part in the version number is increased, all less significant parts are set to 0.
An application version or an OTP version identifies source code versions. That is, it does not imply anything about how the application or OTP has been built.
Order of Versions
Version numbers in general are only partially ordered. However, normal version numbers (with three parts) as of OTP 17.0 have a total or linear order. This applies both to normal OTP versions and normal application versions.
When comparing two version numbers that have an order, one compare each part as ordinary integers from the most significant part towards less significant parts. The order is defined by the first parts of the same significance that differ. An OTP version with a larger version include all changes that that are part of a smaller OTP version. The same goes for application versions.
In the general case, versions may have more than three parts. In this case the versions are only partially ordered. Note that such versions are only used in exceptional cases. When an extra part (out of the normal three parts) is added to a version number, a new branch of versions is made. The new branch has a linear order against the base version. However, versions on different branches have no order. Since they have no order, we only know that they all include what is included in their closest common ancestor. When branching multiple times from the same base version, 0 parts are added between the base version and the least significant 1 part until a unique version is found. Versions that have an order can be compared as described in the paragraph above.
An example of branched versions: The version 126.96.36.199 is a branched version from the base version 6.0.2. Versions on the form 6.0.2.<X> can be compared with normal versions smaller than or equal to 6.0.2, and other versions on the form 6.0.2.<X>. The version 188.8.131.52 will include all changes in 6.0.2. However, 6.0.3 will most likely not include all changes in 184.108.40.206 (note that these versions have no order). A second branched version from the base version 6.0.2 will be version 220.127.116.11.1, and a third branched version will be 18.104.22.168.0.1.
The following application versions were part of OTP 17.0. If the normal part of an applications version number compares as smaller than the corresponding application version in this list, the version number does not adhere to the version scheme introduced in OTP 17.0 and should be considered as not having an order against versions used as of OTP 17.0.