How to mount USB Drive in Single User Mode in Mac OS X

I have faced a problem where my Mac is not booting up and throwing messages like this continuously. process crashed: opendirectoryd. Too many corpses being created. I tried repairing the Hard Disk and re-installing OS, but that didn't fixed the issue. So before i erase the disk and re-install again, i have to backup my files. So i boot-ed up in Single user mode, but i wasn't able to mount the pen drive, as High Sierra prevents loading unsigned kernel extensions, in this instance msdos kext for mounting my FAT formatted pen drive. So i eventually fixed it with the help of online forums and i m putting it together so that it can be useful to others as well.