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# relup

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Release upgrade file

## Description

The release upgrade file describes how a release is upgraded in a running system.

This file is automatically generated by `systools:make_relup/3,4`, using a release resource file (`.rel`), application resource files (`.app`), and application upgrade files (`.appup`) as input.

## File Syntax

In a target system, the release upgrade file is to be located in directory `$ROOT/releases/Vsn`.

The `relup` file contains one single Erlang term, which defines the instructions used to upgrade the release. The file has the following syntax:

    {Vsn,
      [{UpFromVsn, Descr, Instructions}, ...],
      [{DownToVsn, Descr, Instructions}, ...]}.

- `Vsn = string()` - Current release version.

- `UpFromVsn = string()` - Earlier version of the release to upgrade from.

- `Descr = term()` - A user-defined parameter passed from the function `systools:make_relup/3,4`. It is used in the return value of `release_handler:install_release/1,2`.

- `Instructions` - A list of low-level release upgrade instructions, see `appup(4)`. It consists of the release upgrade instructions from the respective application upgrade files (high-level instructions are translated to low-level instructions), in the same order as in the start script.

- `DownToVsn = string()` - Earlier version of the release to downgrade to.

## See Also

`app(4)`, `appup(4)`, `rel(4)`, `release_handler`, `systools`

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