Reading the source code, it seems that error represents any failure from mount(). It seems overlayfs wasn't compiled with my kernel.
- [dev] [ubase] unionfs mount unsupported? Rendov Norra
- [dev] Re: [ubase] unionfs mount unsupported? Rendov Norra
- Re: [dev] Re: [ubase] unionfs mount unsupported? Silvan Jegen
- Re: [dev] Re: [ubase] unionfs mount unsupport... Hiltjo Posthuma
- Re: [dev] Re: [ubase] unionfs mount unsup... Silvan Jegen