Make a copy of your wallet.dat file located here... ~/.bitcoin/wallet.dat
To navigate there on Linux: find / -name wallet.dat -print 2>/dev/null
I'll find the rest of the answer while you're doing that
Once you've got that it's easy mate (might not be the best way but simple and straight forward)... import your wallet.dat file into a blockchain.info wallet here:
https://blockchain.info/wallet/import-walletOpen your blockchain.info wallet and to export private keys:
go to: import/export
select: export unencrypted (from the left hand option bar)
select private key format: bitcoin qt format
from the text in the big box copy the long sequence of letters and numbers in quote marks that follow the word priv.
You're done copy that into your omni Wallet
https://test.omniwallet.org/ (not the hackforums phishing site for fucks sake lol!!)
I'd strongly recommend you send all your bitcoin somewhere secure before doing all this (although chances of being hacked on linux are small compared to windows):
a) you've originally posted a link from hackforums, so if you've got a keylogger or trojan on you're computer attackers could steel your coins.
b) omniwallets only alpha quality so I wouldn't trust it unnecessarily with the $1.7k odd Bitcoin you've got !