It is possible that after installation Cisco PacketTracer7 you will encounter error message: ./PacketTracer7: error while loading shared libraries: libpng12.so.0: cannot open shared object file: No such file or directory. To fix this you have to install missing library libpng12.
PacketTracer requires libpng12.so.0 for its operation. Official documentation or Cisco installation guidebooks lacks of this information. The missing library can be downloaded by typing in the terminal:
# wget -q -O /tmp/libpng12.deb http://mirrors.kernel.org/ubuntu/pool/main/libp/libpng/libpng12-0_1.2.54-1ubuntu1_amd64.deb
Installation of a package with a library.
# dpkg -i /tmp/libpng12.deb
Removing the unnecessary library.
# rm /tmp/libpng12.deb
Cisco PacketTracer7 will be called by command.