https://bz.mercurial-scm.org/show_bug.cgi?id=5541
https://www.illumos.org/issues/8084

--- mercurial-6.8.1/hgext/journal.py.orig
+++ mercurial-6.8.1/hgext/journal.py
@@ -419,6 +419,7 @@
                     )
                     return
                 if not version:
+                    f.seek(0, os.SEEK_SET)
                     # empty file, write version first
                     f.write((b"%d" % storageversion) + b'\0')
                 f.seek(0, os.SEEK_END)