Книга: Linux Network Administrator Guide, Second Edition

File Transfers

File Transfers

Taylor UUCP also allows you to fine-tune file transfers in great detail. At one extreme, you can disable transfers to and from a particular system. Just set request to no, and the remote system will not be able to either retrieve files from your system or send it any files. Similarly, you can prohibit your users from transferring files to or from a system by setting transfer to no. By default, users on both the local and the remote system are allowed to upload and download files.

In addition, you can configure the directories that files may be copied to and from. Usually you will want to restrict access from remote systems to a single directory hierarchy, but still allow your users to send files from their home directory. Commonly, remote users are allowed to receive files only from the public UUCP directory /var/spool/uucppublic. This is the traditional place to make files publicly available, very much like FTP servers on the Internet.[100]

Taylor UUCP provides four different commands to configure the directories for sending and receiving files. They are: local-send, which specifies the list of directories a user may ask UUCP to send files from; local-receive, which gives the list of directories a user may ask to receive files to; and remote-send and remote-receive, which do the analogous for requests from a foreign system. Consider the following example:

system          pablo
...
local-send      /home ~
local-receive   /home ~/receive
remote-send     ~ !~/incoming !~/receive
remote-receive  ~/incoming

The local-send command allows users on your host to send any files below /home and from the public UUCP directory to pablo. The local-receive command allows them to receive files either to the world-writable receive directory in the uucppublic, or any world-writable directory below /home. The remote-send directive allows pablo to request files from /var/spool/uucppublic, except for files from the incoming and receive directories. This is signaled to uucico by preceding the directory names with exclamation marks. Finally, the last line allows pablo to upload files to incoming.

A major problem with file transfers using UUCP is that it receives files only to directories that are world-writable. This may tempt some users to set up traps for other users. However, there's no way to escape this problem outside of disabling UUCP file transfers altogether.

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