What is the test for a federal habeas corpus claim?

To state a cognizable federal habeas corpus claim, the petitioner must assert he is "in custody in violation of the Constitution or laws or treaties of the United States." 28 U.S.C. 2254(a). To satisfy this requirement, the petitioner must allege a nexus between his claims and the unlawful nature of the custody. See Bailey v. Hill, 599 F.3d 976, 978-80 (9th Cir. 2010). In this case, petitioner cannot allege such a nexus because his claims related to enforcement of settlement agreement reached in civil rights actions do not relate to his custody, let alone suggest the unlawful nature of such custody.