Looks like a pathing issues.
instead of find tools under the .../hardware/esp8266 directoy I dont see tools are the error indicates but I see a directrory called 2.5.2. That directory has a bunch of files include a tools directory and then I find the esptool file.
I assume and IDE or esp8266 board libary no keeping up with each other. How do I fix. I have tired to move the tool directory up a couple of levels with a soft link and that didnt seem to fix anything.
fork/exec /home/gary/.arduino15/packages/esp8266/hardware/esp8266/tools/esptool: no such file or directory