遇到的报错信息如下：
root@kali:~# apt-get install w3af
Reading package lists… Done
Building dependency tree
Reading state information… Done
Package w3af is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
E: Package ‘w3af’ has no installation candidate
之前忘记怎么安装成功了，但是这次失败了，查了一下，解决问题如下：
If you’re a Linux, BSD or Mac user we recommend you download the source from our GitHub repository:
git clone --depth 1 https://github.com/andresriancho/w3af.git
cd w3af
./w3af_gui
After running this command you’ll get a list of unmet dependencies and the commands to be run in order to install them. Best case scenario, you’ll have w3af up and running in just a few minutes and only by running the commands returned by w3af_gui.
The framework has two different sets of dependencies, one for the GUI and one for the Console, in case you don’t want to use the GUI, just run w3af_console and install those dependencies.
问题解决。然鹅，幸福从来不会来的那么突然：又报错了，如下
root@kali:~/w3af# ./w3af_gui
Your python installation needs the following modules to run w3af:
pyclamd github git.util pybloomfilter phply nltk tblib pdfminer OpenSSL ndg lxml scapy.config guess_language cluster msgpack ntlm Halberd darts.lib.utils vulndb markdown psutil ds_store termcolor mitmproxy ruamel.ordereddict Flask tldextract pebble acora esmre bravado xdot
After installing any missing operating system packages, use pip to install the remaining modules:
sudo pip install pyClamd==0.4.0 PyGithub==1.21.0 GitPython==2.1.3 pybloomfiltermmap==0.3.14 phply==0.9.1 nltk==3.0.1 tblib==0.2.0 pdfminer==20140328 pyOpenSSL==17.4.0 ndg-httpsclient==0.3.3 lxml==3.4.4 scapy-real==2.2.0-dev guess-language==0.2 cluster==1.1.1b3 msgpack-python==0.4.4 python-ntlm==1.0.1 halberd==0.2.4 darts.util.lru==0.5 vulndb==0.0.19 markdown==2.6.1 psutil==2.2.1 ds-store==1.1.2 termcolor==1.1.0 mitmproxy==0.13 ruamel.ordereddict==0.4.8 Flask==0.10.1 tldextract==1.7.2 pebble==4.3.6 acora==2.1 esmre==0.3.1 bravado==9.2.2 xdot==0.6
A script with these commands has been created for you at /tmp/w3af_dependency_install.sh
The required “dot” binary is missing, please install the “graphviz” package in your operating system.
耐心读一下，缺少一些小小的支持、库文件啥的。而且已经在/tmp/w3af_dependency_install.sh创建好了。那么就安装。
./tmp/weaf_dependency_install.sh进行安装即可。当然，下载的速度是非常漫长的。不过，好在我的耐心还是比较充足的。等待下载完毕。然后顺手install了一个graphviz
接着：
root@kali:~/tmp# apt-get build-dep python-lxml