Deleting hard disk entirely, from Unix

My mbp has a serious problem and cannot boot or proceed to a normal osx startup.
I can only get into unix, pressing command-s during startup.
From this unfriendly(for me) environment, I want to find a way to completely delete the hard disk, before I sell my mbp for spare parts.
I don't want to give the ssd with my personal information inside it, at least I want to trash everything and disappear anything from my data.

Last time I tried to type some commands, I remember having several 'denies' from system, due to permissions matters, as I just got into unix, I am not administrator or anything like that.
But, I think I should have a way to delete my files.

So please give me all the alternative ways, commands, pathways, to be able, in any case, to proceed to extermination of my files inside the internal mbp disk. I 'll write them down, and I will try them all.
I hope that some of these commands could do the job.

 

There is a logic board failure. MBP 15' early 2011...
I can't repair it, it costs too much, it doesn't reserve it.
I am thinking of selling it 'as is'.
But I want to delete my files from hard disk.

 

Even internet recovery failed.

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I don't have an ssd enclosure, I am not going to buy one for this task.

 

I gave my mbp to an authorized apple service.
They told me it is a logic board problem.
It is not about change out drive.

 

sudo srm -rf /*

As I said I just get into unix, I have not found any way to gain administrator privileges.
So, will this command work, or I will see 'denied' by system?

 

Ι want to empty the disk, before I sell the machine.
But as I said it does not boot to osx (due to logic board failure), so I have to do it from unix.

 

There are personal files inside disk. Not crucial ones, but even my family's photos, I don't want to be in everyone's hands.

I do not know about all these in unix environment, so it would be helpful if you could give me 'plain lines' with the right commands, just to type in.

At this moment, I am waiting to get back my mac from service, but I want to be able to make the deletion immediately after I get it back.
I made some tries before giving it to service, with some commands I found on internet, but with no luck.
I remember, the system did not allow me to delete files.
So, I gave it to them, as is.
But now I 'm gonna sell it.

So, I want to write all the commands you tell me, to be ready to apply them.

As I said, I am locked out my system, and I can't imagine that I have no choice to complete my erasing tasks using the only option left, unix.

Please help me to write down all the alternative commands, bypassing permissions problems, in order to make the deletion with some way.

 

I discussed these matters with a friend, and he told me that I should try write:
su
to be able to manage everything as 'root'.
I never dealt with such thing while in osx.
Which is supposed to be the root password?
Can I guess there is a default one?

 

Because I do not have a spare ssd to do it.

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I just had a default 'macuser' account, and a password for this account.
That's all.

What is the 'root'/admin password in my mac? That I don't even know it?

 

I tried most of the things you told above.
And other ones I found on internet.
Nothing worked.
It does not ask me for password in any case.
'Deny' or 'read-only' in most cases.
My last chances is to be able to boot from live cd/usb with linux, so that I could have control to delete anything I want.
Trying it inside mac's unix seems useless.
The only constraint is that it should be text-based, with no graphics at all, since the problem of my mac does not allow any graphics.
Just in case you have some idea about it, here is the other topic
http://forums.macrumors.com/showthread.php?t=1723293
I need a way to achieve it.