As explained here
How the Liquibase classpath worked before version 4.0
Before version 4.0, one of the default locations Liquibase added to
the classpath was the root directory in your filesystem (/). The
change caused issues because of a machine-dependent changelog path,
such as /home/my-user/projects/liquibase/changelog.xml, found under
the / directory. This way, Liquibase uses the given path as part of
the changeset identifier stored in the DATABASECHANGELOG table, and
when you run Liquibase from
/home/other-user/projects/liquibase/changelog.xml, Liquibase sees it
as a different changelog and tries to rerun all the previously run
changesets.
To prevent identification issues from happening, a / was removed as a
default part of the classpath. How the Liquibase classpath works in
4.0 and later versions
Starting with Liquibase 4.0, the root directory (/) is no longer a
default part of the classpath because of the issue mentioned in the
previous section.
...
The message "Please use a relative path or add '/' to the classpath parameter." refers to the root directory '/', and does not mean to add a slash to the start of your classpath path. Afaik, classpath:x
and classpath:/x
are the same.
Also, the message appears when the master changelog is not found, for whatever reason, so also a typo can cause this message. It's only a hint telling you that it might not be found because the file is not on the classpath, because they removed the root directory from the classpath, but it could also not be found because you specified the wrong path (I just did that).
To configure it correctly, the master changelog must be on the Liquibase classpath. In Spring Boot, the Liquibase classpath is set to the application's classpath, i.e. you can use src/main/resources
.
Tl;dr: When your file is src/main/resources/db/changelog/db.changelog-master.xml
use
spring.liquibase.change-log=classpath:/db/changelog/db.changelog-master.xml
I don't know, whether there was or is a bug in regards to that with certain Liquibase versions, but that's how it's supposed to work, anyway.