vsftpd-1.1.3配制实例之五：VIRTUAL_USERS

　　This example shows how to set up vsFTPd / PAM with "virtual users".
　　A virtual user is a user login which does not exist as a real login on the
　　system. Virtual users can therefore be more secure than real users, beacuse
　　a compromised account can only use the FTP server.
　　Virtual users are often used to serve content that should be Accessible to untrusted users, but not generally accessible to the public.
　　Step 1) Create the virtual users database.
　　We are going to use pam_userdb to authenticate the virtual users. This needs
　　a username / passWord file in "db" format - a common database format.
　　To create a "db" format file, first create a plain text files with the
　　usernames and password on alternating lines.
　　See example file "logins.txt" - this specifies "tom" with password "foo" and
　　"fred" with password "bar".
　　Whilst logged in as root, create the actual database file like this:
　　db_load -T -t hash -f logins.txt /etc/vsftpd_login.db
　　(Requires the Berkeley db program installed).
　　This will create /etc/vsftpd_login.db. Obviously, you may want to make sure
　　the permissions are restricted:
　　chmod 600 /etc/vsftpd_login.db
　　For more information on maintaing your login database, look around for
　　documentation on "Berkeley DB", e.g.
　　http://www.sleepycat.com/docs/utility/index.Html
　　Step 2) Create a PAM file which uses your new database.
　　See the example file vsftpd.pam. It contains two lines:
　　auth required /lib/security/pam_userdb.so db=/etc/vsftpd_login
　　account required /lib/security/pam_userdb.so db=/etc/vsftpd_login
　　This tells PAM to authenticate users using our new database. Copy this PAM
　　file to the PAM Directory - typically /etc/pam.d/
　　cp vsftpd.pam /etc/pam.d/ftp
　　Step 3) Set up the location of the files for the virtual users.
　　useradd -d /home/ftpsite virtual
　　ls -ld /home/ftpsite
　　(which should give):
　　drwx------ 3 virtual virtual 4096 Jul 30 00:39 /home/ftpsite
　　We have created a user called "virtual" with a home directory "/home/ftpsite".
　　Let's add some content to this download area:
　　cp /etc/hosts /home/ftpsite
　　chown virtual.virtual /home/ftpsite/hosts
　　Step 4) Create your vsftpd.conf config file.
　　See the example in this directory. Let's go through it line by line:
　　anonymous_enable=NO
　　local_enable=YES
　　This disables anonymous FTP for security, and enables non-anonymous FTP (which
　　is what virtual users use).
　　write_enable=NO
　　anon_upload_enable=NO
　　anon_mkdir_write_enable=NO
　　anon_other_write_enable=NO
　　These ensure that for security purposes, no write commands are allowed.
　　chroot_local_user=YES
　　This makes sure that the virtual user is restricted to the virtual FTP area
　　/home/ftpsite we set up above.
　　guest_enable=YES
　　guest_username=virtual
　　The guest_enable is very important - it activates virtual users!
And
　　guest_username says that all virtual users are mapped to the real user
　　"virtual" that we set up above. This will also determine where on the
　　filesystem the virtual users end up - the home directory of the user
　　"virtual", /home/ftpsite.
　　listen=YES
　　listen_port=10021
　　This puts vsftpd in "standalone" mode - i.e. not running from an inetd. This
　　means you just run the vsftpd executable and it will start up. This also
　　makes vsftpd listen for FTP requests on the non-standard port of 10021 (FTP
　　is usually 21).
　　pasv_min_port=30000
　　pasv_max_port=30999
　　These put a port range on passive FTP incoming requests - very useful if
　　you are configuring a firewall.
　　Copy the example vsftpd.conf file to /etc:
　　cp vsftpd.conf /etc/
　　Step 5) Start up vsftpd.
　　Go to the directory with the vsftpd binary in it, and:
　　./vsftpd
　　If all is well, the command will sit there. If all is not well, you will
　　likely see some error message.
　　Step 6) Test.
　　Launch another shell session (or background vsftpd with CTRL-Z and then "bg").
　　Here is an example of an FTP session:
　　ftp localhost 10021
　　Connected to localhost (127.0.0.1).
　　220 ready, dude (vsFTPd 1.1.0: beat me, break me)
　　Name (localhost:chris): tom
　　331 Please specify the password.
　　Password:
　　230 Login sUCcessful. Have fun.
　　Remote system type is UNIX.
　　Using binary mode to transfer files.
　　ftp> pwd
　　257 "/"
　　ftp> ls
　　227 Entering Passive Mode (127,0,0,1,117,135)
　　150 Here comes the directory listing.
　　226 Transfer done (but failed to open directory).
　　ftp> size hosts
　　213 147
　　ftp>
　　Comments:
　　The password we gave was "foo".
　　Do not be alarmed by the "failed to open directory". That is because the
　　directory /home/ftpsite is not world readable (we could change this
　　behaviour if we wanted using anon_world_readable_only=NO but maybe we want
　　it this way for security.
　　We can see that we have access to the "hosts" file we copied into the virtual
　　FTP area, via the size command.
　　logins.txt
　　tom
　　foo
　　fred
　　bar
　　vsftpd.conf
　　anonymous_enable=NO
　　local_enable=YES
　　write_enable=NO
　　anon_upload_enable=NO
　　anon_mkdir_write_enable=NO
　　anon_other_write_enable=NO
　　chroot_local_user=YES
　　guest_enable=YES
　　guest_username=virtual
　　listen=YES
　　listen_port=10021
　　pasv_min_port=30000
　　pasv_max_port=30999
　　vsftpd.pam
　　auth required /lib/security/pam_userdb.so db=/etc/vsftpd_login
　　account required /lib/security/pam_userdb.so db=/etc/vsftpd_login
　　VIRTUAL_USERS_2
　　This example shows how to extend the "VIRTUAL_USERS" example to reflect
　　a slightly more complex setup.
　　Let's assume that we want two types of virtual user - one that can only browse
　　and download content, and another that can upload new content as well as
　　download existing content.
　　To achieve this setup, we can use use of vsftpd's powerful per-user
　　configurability (new in v1.1.0).
　　In the previous virtual user example, we created two users - tom and fred.
　　Let's say that we want fred to have write access to upload new files whilst
　　tom can only download.
　　Step 1) Activate per-user configurability.
　　To activate this powerful vsftpd feature, add the following to
　　/etc/vsftpd.conf:
　　user_config_dir=/etc/vsftpd_user_conf
　　And, create this directory:
　　mkdir /etc/vsftpd_user_conf
　　Step 2) Give tom the ability to read all files / directories.
　　At the end of the last example, we noted that the virtual users can only
　　see world-readable files and directories. We could make the /home/ftpsite
　　directory world readable, and upload files with world-read permission. But
　　another way of doing this is giving tom the ability to download files which
　　are not world-readable.
　　For the tom user, supply a config setting override for
　　anon_world_readable_only:
　　
　　echo "anon_world_readable_only=NO" > /etc/vsftpd_user_conf/tom
　　Check it out - login as tom and now "ls" will return a directory listing!

　　Log in as fred and it won't.
　　NOTE - restart vsftpd to pick up the config setting changes to
　　/etc/vsftpd.conf. (Advanced users can send SIGHUP to the vsftpd listener
　　process).
　　Step 3) Give fred the ability to read all files / directories and create
　　new ones but not interfere with existing files.
　　echo "anon_world_readable_only=NO" > /etc/vsftpd_user_conf/fred
　　echo "write_enable=YES" >> /etc/vsftpd_use