The root cause is gethostbyname() in the following libsynthesis code:

src/platform_adapters/linux/configfiles.cpp

bool getLocalDeviceID(string &aURI)
...
  if (gethostname(szHostname, sizeof(szHostname))!=0) {
    hostName="_unknown_";
  }
  else {
    // get host entry
    pHostEnt = gethostbyname(szHostname);
    // return fully qualified name of machine as ID
    if (pHostEnt)
      hostName=pHostEnt->h_name; // DNS name of machine
    else
      hostName=szHostname; // just name of machine
  }
...

I suppose the code above tries to resolve the canonical host name. I am not
sure whether that is really useful, so perhaps the call can simply be removed
without any ill effects. It certainly doesn't matter for PBAP syncing.