title: Fast concatenate multiple files on Linux
body: <p>I am using Python multiprocessing to generate a temporary output file per process. They can be several GBs in size and I make several tens of these. These temporary files need to be concated to form the desired output and this is the step that is proving to be a bottleneck (and a parallelism killer). Is there a Linux tool that will create the concated file by modifying the file-system meta-data and not actually copy the content ? As long as it works on any Linux system that would be acceptable to me. But a file system specific solution wont be of much help.</p>
  
  <p>I am not OS or CS trained, but in theory it seems it should be possible to create a new inode and copy over the inode pointer structure from the inode of the files I want to copy from, and then unlink those inodes. Is there any utility that will do this ? Given the surfeit of well thought out unix utilities I fully expected it to be, but could not find anything. Hence my question on SO. The file system is on a block device, a hard disk actually, in case this information matters. I dont have the confidence to write this on my own, as I have never done any systems level programming before,  so any pointers (to C/Python code snipppets) will be very helpful.</p>