In practice, 'system config-management commit-revisions' is set, as a result of an entry in the default config. However, there is nothing preventing it from being removed. For availability of 'soft rollback' (T5249), and for efficiency of tests 'compare saved' and warnings on unsaved configs, it is desirable to have a default value for commit revisions, and initialization of the post-commit hook 01vyos-commit-revision.