Search in a big file for specific word

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http://askubuntu.com – I have a 6GB text file, it have an access record for a whole month to my website. That file is my only hope to know how a kiddie got access to my website and hack it. but as the file is too big so gedit couldn't open it due to memory leak. is there's any command or method I could do to read or search in the content of that file ? I tried the following command grep -i '18/jan' 02records but it take a while then no results shows. all i need is any line that have '18/jan' word Thanks (HowTos)