This document describes optional extensions to the language described in the hosts_access(5) document. The extensions are enabled at program build time. For example, by editing the Makefile and turning on the PROCESS_OPTIONS compile-time option.
The extensible language uses the following format:
daemon_list : client_list : option : option ...
The first two fields are described in the hosts_access(5) manual page. The remainder of the rules is a list of zero or more options. Any
Grant (deny) service. These options must appear at the end of a rule.
The allow and deny keywords make it possible to keep all access control rules within a single file, for example in the hosts.allow file.
To permit access from specific hosts only:
ALL: .friendly.domain: ALLOW ALL: ALL: DENY
To permit access from all hosts except a few trouble makers:
ALL: .bad.domain: DENY ALL: ALL: ALLOW
Execute, in a child process, the specified shell command, after performing the %
spawn (/usr/sbin/safe_finger -l @%h | /usr/bin/mail root) executes, in a background child process, the shell command
The example uses the
Replace the current process by an instance of the specified shell command, after performing the %
To send a customized bounce message to the client instead of running the real ftp daemon:
in.ftpd : ... : twist /bin/echo 421 Some bounce message For an alternative way to talk to client processes, see the banners option below.
To run /some/other/in.telnetd without polluting its command-line array or its process environment:
Causes the server to periodically send a message to the client. The connection is considered broken when the client does not respond. The keepalive option can be useful when users turn off their machine while it is still connected to a server. The keepalive option is not useful for datagram (UDP) services.
rfc931 [ timeout_in_seconds?
Look for a file in `/some/directory' with the same name as the daemon process (for example in.telnetd for the telnet service), and copy its contents to the client. Newline characters are replaced by carriage-return newline, and %
The tcp wrappers source code distribution provides a sample makefile (Banners.Makefile) for convenient banner maintenance.
Warning: banners are supported for connection-oriented (TCP) network services only.
nice [ number?
Change the nice value of the process (default 10). Specify a positive value to spend more CPU resources on other processes.
setenv name value
Place a (name, value) pair into the process environment. The value is subjected to %
Warning: many network daemons reset their environment before spawning a login or shell process.
Like the umask command that is built into the shell. An umask of 022 prevents the creation of files with group and world write permission. The umask argument should be an octal number.