all i had to say is sayed - and if i ever here stories about "sda" or "sdb" three things might happend:
a) it might be that i run away screeming
b) it might be that i get angry
c) it might be that i get angry and run away screeming
So please do us a favour and don't let it come so far - and please never ever use or talk about "sda" or "sdb" - i don't know the internal implementation of Apples UEFI - but a normal UEFI loader should look like that:
# efibootmgr -v :(
BootCurrent: 0001
Timeout: 0 seconds
BootOrder: 0001,0002,0000,0003,0004
Boot0000* Windows Boot Manager HD(1,GPT,fb9d1a2b-6546-463c-a6ca-32f29fd8c720,0x800,0x113000)/File(\EFI\Microsoft\Boot\bootmgfw.efi)WINDOWS.........x...B.C.D.O.B.J.E.C.T.=.{.9.d.e.a.8.6.2.c.-.5.c.d.d.-.4.e.7.0.-.a.c.c.1.-.f.3.2.b.3.4.4.d.4.7.9.5.}....................
Boot0001* siduction HD(1,GPT,fb9d1a2b-6546-463c-a6ca-32f29fd8c720,0x800,0x113000)/File(\EFI\siduction\grubx64.efi)
Boot0002* debian HD(1,GPT,fb9d1a2b-6546-463c-a6ca-32f29fd8c720,0x800,0x113000)/File(\EFI\debian\shimx64.efi)
Boot0003* arch HD(1,GPT,fb9d1a2b-6546-463c-a6ca-32f29fd8c720,0x800,0x113000)/File(\EFI\arch\grubx64.efi)
Boot0004* Hard Drive BBS(HD,,0x0)AMGOAMNO........u.C.r.u.c.i.a.l._.C.T.5.2.5.M.X.3.0.0.S.S.D.1....................A.................................>..Gd-.;.A..MQ..L. . . . . . . . .6.1.4.4.4.1.2.8.D.5.9.9......AMBOAMNO........o.C.r.u.c.i.a.l._.C.T.5.2.5.M.X.3.0.0.S.S.D.1....................A...........................>..Gd-.;.A..MQ..L. . . . . . . . .6.1.6.4.4.1.F.A.3.7.5.E......AMBOAMNO........o.C.r.u.c.i.a.l._.C.T.5.2.5.M.X.3.0.0.S.S.D.1....................A...........................>..Gd-.;.A..MQ..L. . . . . . . . .6.1.8.3.3.1.6.F.2.7.E.F......AMBOAMNO........o.S.a.m.s.u.n.g. .S.S.D. .8.4.0. .P.R.O. .S.e.r.i.e.s....................A...........................>..Gd-.;.A..MQ..L.1.S.R.2.E.N.D.A.2.1.8.8.7.3. .N. . . . ......AMBOAMNO........o.S.a.m.s.u.n.g. .S.S.D. .8.5.0. .E.V.O. .2.5.0.G.B....................A...........................>..Gd-.;.A..MQ..L.2.S.P.1.X.N.G.A.3.8.2.8.5.7. .X. . . . ......AMBOAMNO........o.S.T.3.0.0.0.V.N.0.0.0.-.1.H.J.1.6.6....................A...........................>..Gd-.;.A..MQ..L. . . . . . . . . . . . .6.W.1.A.Z.P.P.D......AMBOAMNO........o.S.T.3.0.0.0.V.N.0.0.0.-.1.H.J.1.6.6....................A...........................>..Gd-.;.A..MQ..L. . . . . . . . . . . . .6.W.2.A.Q.4.Y.Y......AMBO
and this loader points to the efi dir at exactly this drive :
HD(1,GPT,fb9d1a2b-6546-463c-a6ca-32f29fd8c720,0x800,0x113000)/File(\EFI\siduction\grubx64.efi)
thats all - basically - and it would be nice if ther would be only one linux entry - hmm - maybe two, one as fall back. One will see that siduction is my default loader - right now cala can mess this up, not the best idea ever. Second thing that can happend: the nvram filesystem is simply full after some time, can lead to funny bugs - one can google for it.