Yesterday I started running a job with a script for blast. An output file was created. now, almost 24 hours later, the file is still empty, no other files were created, and the job keeps running. I think it won't stop unless I'll stop it. I was told that it might be due to a contig that's too long.
Maybe it's important to note that initially I couldn't keep the job running, since it kept failing due to memory limit exceeding. To overcome this I set a higher limit of 100gb. That's the highest I ever had to set.
I already answered this question in the other thread you started.
Files are written in chunks that correspond to sector sizes. BLAST will not have written enough output to go over a sector size until it completes a search with at least one sequence, as hits for each sequence are written at the end. As long as the search is still ongoing with the very first query sequences (assuming you have more than one), it is possible that there will be no output in that file.
There could be multiple explanations: your computer is slow (either objectively, or because it is shared with many other people); 100 Gb is still not enough so there is lots of disk swapping, which makes everything slow; you have a long query sequence that takes a while to search; all of the above.
I suggest you take a shorter query sequence and a smaller database, and run a test to make sure that everything works. Assuming it does, you may need more than 100Gb of memory assigned, a smaller database, or a faster computer. If all of that fails, you will need more patience.