If a § 2241 petition is not barred when it follows a § 2255 petition, and if a § 2255 petition is not barred when it follows a § 2241 petition, a fortiori, a § 2241 petition that follows an earlier § 2241 petition cannot be barred. Not only are Zakiya’s successive § 2241 claims permissible, but they are entirely appropriate. When a § 2255 petition proves “inadequate or ineffective to test the legality of detention, a federal prisoner may seek a writ of habeas corpus pursuant to” § 2241. In re Vial, 115 F.3d 1192, 1194 (4th Cir.1997) (internal ellipses omitted). In fact, § 2241 is the only mechanism for a prisoner to challenge the execution, as opposed to the validity, of his federal sentence. See United States v. Addonizio, 442 U.S. 178, 185-86, 99 S.Ct. 2235, 60 L.Ed.2d 805 (1979) (<HOLDING>); In re Vial, 115 F.3d at 1194 n. 5 (“attacks
holding that an attack on the computation and execution of a sentence must come in the form of a  2241 petition holding that  2255 is unavailable to attack execution of sentence holding that defendant cannot successfully challenge legal sentence or attack underlying conviction through motion for sentence reconsideration holding that it is well settled in this jurisdiction and elsewhere that  2255 will lie only to attack the imposition of a sentence and that an attack on the execution thereof may be accomplished only by way of habeas corpus in the district of confinement holding that a petition under  2241 attacks the execution of a sen tence while a  2255 petition attacks the validity of a judgment and sentence