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The application upgrade file defines how an application is upgraded in a running system.
This file is used by systools to generate release
upgrade files.
Applications can be upgraded and the instructions to do this are placed in the .appup file for the application. For example, for the snmp application these instructions are placed in the snmp.appup file. The .appup file looks as follows:
The application upgrade file is called Name.appup where
Name is the name of the application. The file should be
located in the ebin directory for the application.
The .appup file contains one single Erlang term, which
defines the instructions used to upgrade the application. The
file has the following syntax:
{Vsn,
[{UpFromVsn, UpFromScript}, ...],
[{DownToVsn, DownToScript}, ...]}.
Vsn = string() is the current version of the
application.
UpFromVsn = string() is a version we can upgrade
from.
UpFromScript is the script which describes the
sequence of release upgrade instructions. Refer to the
section Release Handling Instructions in the SASL User's Guide
for a description of this script.
DownToVsn = string() is a version to which we can
downgrade.
DownToScript is the script which describes the
sequence of downgrade instructions. Refer to the
section Release Handling Instructions in the SASL User's Guide
for a description of this script.
In the case of UpFrom Script and DownFromScript,
the scripts typically contain one line for each module in the
application.
app(4), relup(4), systools(3)