I finally had a little success !
The fix suggested by Hive account@abit worked alright - It was my fault.
Steemd replayed, started a witness, synced and started mining.

(Yeah)

The whole thing is pointless, though.

There is a bug.

So I won't be able to show off a POW.

Nobody is back in the miner queue with his Supercomputing accounts.

(picture taken from steemdb.com)

It looks like two people can exploit this bug.

I hope it gets fixed quickly and that I can get the miner running quickly after the next fork.

Thanks Hive account@abit and Hive account@smooth for taking the time to help me.

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Can you spot the difference ?

sudo mount -o remount,size=10G /dev/shm

works.

sudo mount -o remount, size=10G /dev/shm

doesn't work.

Maybe I can skip avoidable mistakes like that next time.

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Here is a picture of my miner hashing:

(For proof)

I'm waiting for the bugfix now.

Steem on !