Avamar: What is the cause of the error message "WARN: <1258> xmldocerrorhandler: Entity: line 1: parser error: xmlParseEntityRef warnings"

The error message seen in the gsan.log:

WARN: <1258> xmldocerrorhandler: Entity: line 1: parser error : xmlParseEntityRef

The gsan.log shows that the root cause of this issue is a "wrap up" message from avtar that contains invalid XML content.

This warning is due to an inability to parse the name of a file that is being backed up in the wrap-up message.

The most common cause is a filename with special characters in the name.

There are five characters that must be escaped for XML to parse the filename.
(See the Resolution section for a list of characters.)

In this example, the ampersand "&" character causes the issue.

2021/11/14-19:04:56.64046 {0.0} [srvm-563941198#srv:2709] WARN: <1258> xmldocerrorhandler: Entity: line 1: parser error : xmlParseEntityRef: no name 
2021/11/14-19:04:56.65398 {0.0} [srvm-563941198#srv:2709] WARN: <1258> xmldocerrorhandler: L\localhost\Policies\User\Documents & 
2021/11/14-19:04:56.65402 {0.0} [srvm-563941198#srv:2709] WARN: <1258> xmldocerrorhandler:               ^

The XML is invalid because the "&" in the file name is not escaped, as required by XML.

These are the escape codes for the five characters where XML requires escape.
(There are a few exceptions that are allowed for embedded quotes of different types, but it is safe to ALWAYS ESCAPE.)

This warning can be ignored from a server perspective, though it is possible that the file name makes it difficult to restore that file, if necessary.