Matthias wrote: > Are you sure that also the corresponding -dev packets are installed? > Perhaps you just have the libs but not the needed headers installed. That's right. In fact, I made a couple of mistakes. I just did a fresh reinstall test of Debian Lenny (on a VM) and this time I allowed it to download packages from the network during the install. Now an "apt-cache search libcap" reports many other libcap* packages. I installed all necessary packages and compiled squid with the full options for Linux (as explained in the Squid wiki) in addition to --enable-linux-netfilter. Compiling and making was successful this time. Thank you very much for your help.
