How can I monitor an installer as it modifies the filesystem on Yosemite? fseventer does not support Yosemite until further notice and the suggestions here don't work for me so how can I monitor an installer as it writes files to the file system? I also tried Sloth but it only shows currently open files at a specific point in time.
This not application specific (it will show all) but you can find the one you are looking for.

iosnoop

This “traces” disk I/O execution live. Each time a disk I/O completes, a line of output is printed to summarize it, including process name and filename details:

Example:

sudo iosnoop

UID   PID D    BLOCK   SIZE       COMM PATHNAME

  503 54079 R 286522800   4096 Google Chrome ??/Cache/data_2