Hello. Last week, I tried to downgrade the version of librealsense2(2.16.4-0~realsense0.127) to librealsense2(2.8.1-0~realsense0.41) for using this facedetector library.(http://wiki.ros.org/facedetector) Like this...↓

$ dpkg -l | grep "realsense" | cut -d " " -f 3 | xargs sudo dpkg --purge //delete all of librealsense
$ sudo apt install librealsense2-udev-rules=2.8.1-0~realsense0.41
$ sudo apt install librealsense2-dkms=1.3.1-0ubuntu3
$ sudo apt install librealsense2=2.8.1-0~realsense0.41
$ sudo apt install librealsense2-utils=2.8.1-0~realsense0.41
$ sudo apt install librealsense2-dev=2.8.1-0~realsense0.41
$ sudo apt install librealsense2-dbg=2.8.1-0~realsense0.41

But it couldnt work,so I upgrade librealsense2(2.17.0-0~realsense0.256).

$ dpkg -l | grep "realsense" | cut -d " " -f 3 | xargs sudo dpkg --purge //delete all of librealsense
$ sudo apt install librealsense2-udev-rules=2.17.0-0~realsense0.256
$ sudo apt install librealsense2-dkms
$ sudo apt install librealsense2=2.17.0-0~realsense0.256
$ sudo apt install librealsense2-utils
$ sudo apt install librealsense2-dev
$ sudo apt install librealsense2-dbg

Then I tried realsense-viewer v2.17.0 ,I couldn't find realsense. And I often use ROS, so I tried

$ roslaunch realsense2_camera rs_rgbd.launch 
[ERROR] [1544361373.995566111]: Failed to load nodelet [/camera/realsense2_camera] of type [realsense2_camera/RealSenseNodeFactory] even after refreshing the cache: API version mismatch: librealsense.so was compiled with API version 2.17.0 but the application was compiled with 2.16.1! Make sure correct version of the library is installed (make install)

So, something version2.61.1 is left, but I couldnt find where it is... How can I use librealsense v2.17.0-0?

Add Information(2018/12/11) These are file's name which has the character "librealsense", what I have. I dont know, how can I compile the application with 2.17.0. If someone knows, it will be helpful if you tell me, please.

$ apt search librealsense
librealsense2/xenial 2.17.0-0~realsense0.256 amd64
Intel(R) RealSense(tm) Cross Platform API - runtime

librealsense2-dbg/xenial 2.17.0-0~realsense0.256 amd64
Intel(R) RealSense(tm) Camera Capture API - debug symbols

librealsense2-dev/xenial 2.17.0-0~realsense0.256 amd64
Intel(R) RealSense(tm) Camera Capture API - development files

librealsense2-dkms/xenial 1.3.4-0ubuntu1 all
Modified kernel modules for librealsense2

librealsense2-udev-rules/xenial 2.17.0-0~realsense0.256 amd64
Intel(R) RealSense(tm) Camera Capture API - udev rules

librealsense2-utils/xenial 2.17.0-0~realsense0.256 amd64
Intel(R) RealSense(tm) Camera Capture API - utils and demos

realsense-sdk-dev/xenial 2.7.7-0~realsense0.29 amd64
Intel(R) RealSense(tm) Camera Capture API - development files

realsense-sdk-utils/xenial 2.7.7-0~realsense0.29 amd64
Intel(R) RealSense(tm) Camera Capture API - utils and demos

ros-kinetic-librealsense/xenial 1.12.1-0xenial-20180809-140204-0800 amd64
Library for capturing data from the Intel(R) RealSense(TM) F200, SR300, R200, LR200 and ZR300 cameras.

Please excuse me if you may not understand or you feel bad with my poor English.