Category Archives: Lab blog

Linux security tips and tricks

So you want to allow users to upload files to your server? This can be dangerous, very quickly someone will upload a malicious PHP script that allows them access to the directories of your web applications.

Here are some tips and tricks to aid in the safety of your server. We use all of these, and some others that are not included here so that the bad guys can’t figure out all of our security approaches!

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Reading and writing to the same file

If you try to modify a file (removing all empty lines for example) using a command like:

 cat file.txt | sed '/^$/d' > file.txt 

you will end up with and empty file.txt. The reason is that bash parses the command line looking for “metacharacters” (  “|” , “>” and “space”  in this case) that separate words, then groups and executes those words according to their precedence. This means that “> file.txt”  get executed FIRST. This creates an empty file.txt (overwriting any existing file) and a “process”  to redirect standard output to that file. Then “cat file.txt” get executed, but by now file.txt is empty. So “cat file.txt” outputs 0 lines,  “sed ‘/^$/d’ ” deletes all 0 empty lines, and 0 lines get written to file.txt . This works as “intended” and bash outputs no error.

You can get around this using a temporal file.

 cat file.txt | sed '/^$/d' > tmp_file.txt
mv tmp_file.txt file.txt
 

But, as file.txt is technically a new file you might lose some information, in particular permissions and whether file.txt was originally a symbolic link or not.

Other options is to use sponge, which is part of moreutils and sadly not standard in many systems.

 cat file.txt | sed '/^$/d' | sponge file.txt
 

 

SoCal Hackathon 2018

We are pleased to announce the SoCal Bioinformatics Hackathon.

From 10-12 January, 2018, the NCBI will help run a bioinformatics hackathon in Southern California hosted by San Diego State University!  The hackathon will focus on advanced bioinformatics analysis of next generation sequencing data, proteomics, and metadata. This event is for researchers, including students and postdocs, who have already engaged in the use of bioinformatics data or in the development of pipelines for bioinformatics analyses from high-throughput experiments. Some projects are available to other non-scientific developers, mathematicians, or librarians.

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