/usr/include/ptlib/unix/ is in libpt-dev 2.10.11~dfsg-2.1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/ptlib/unix/ptlib/
/usr/include/ptlib/unix/ptlib/beaudio.h
/usr/include/ptlib/unix/ptlib/bevideo.h
/usr/include/ptlib/unix/ptlib/channel.h
/usr/include/ptlib/unix/ptlib/conchan.h
/usr/include/ptlib/unix/ptlib/config.h
/usr/include/ptlib/unix/ptlib/contain.h
/usr/include/ptlib/unix/ptlib/critsec.h
/usr/include/ptlib/unix/ptlib/dynalink.h
/usr/include/ptlib/unix/ptlib/ethsock.h
/usr/include/ptlib/unix/ptlib/file.h
/usr/include/ptlib/unix/ptlib/filepath.h
/usr/include/ptlib/unix/ptlib/icmpsock.h
/usr/include/ptlib/unix/ptlib/ipdsock.h
/usr/include/ptlib/unix/ptlib/ipsock.h
/usr/include/ptlib/unix/ptlib/maccoreaudio.h
/usr/include/ptlib/unix/ptlib/mail.h
/usr/include/ptlib/unix/ptlib/mutex.h
/usr/include/ptlib/unix/ptlib/pdirect.h
/usr/include/ptlib/unix/ptlib/pipechan.h
/usr/include/ptlib/unix/ptlib/pmachdep.h
/usr/include/ptlib/unix/ptlib/pprocess.h
/usr/include/ptlib/unix/ptlib/ptime.h
/usr/include/ptlib/unix/ptlib/ptlib.inl
/usr/include/ptlib/unix/ptlib/remconn.h
/usr/include/ptlib/unix/ptlib/resampler.h
/usr/include/ptlib/unix/ptlib/semaphor.h
/usr/include/ptlib/unix/ptlib/serchan.h
/usr/include/ptlib/unix/ptlib/sfile.h
/usr/include/ptlib/unix/ptlib/shmvideo.h
/usr/include/ptlib/unix/ptlib/socket.h
/usr/include/ptlib/unix/ptlib/sound.h
/usr/include/ptlib/unix/ptlib/svcproc.h
/usr/include/ptlib/unix/ptlib/syncpoint.h
/usr/include/ptlib/unix/ptlib/tcpsock.h
/usr/include/ptlib/unix/ptlib/textfile.h
/usr/include/ptlib/unix/ptlib/thread.h
/usr/include/ptlib/unix/ptlib/timeint.h
/usr/include/ptlib/unix/ptlib/timer.h
/usr/include/ptlib/unix/ptlib/udpsock.h
/usr/include/ptlib/unix/ptlib/video.h