HOSTS_OPTIONS

HOSTS_OPTIONS

NAME DESCRIPTION LOGGING ACCESS CONTROL RUNNING OTHER COMMANDS NETWORK OPTIONS USERNAME LOOKUP MISCELLANEOUS DIAGNOSTICS SEE ALSO AUTHOR

NAME

hosts_options - host access control language extensions

DESCRIPTION

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

An option is of the form

LOGGING

severity mail.info

severity notice

Change the severity level at which the event will be logged. Facility names (such as mail) are optional, and are not supported on systems with older syslog implementations. The severity option can be used to emphasize or to ignore specific events.

ACCESS CONTROL

allow

deny

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

Notice the leading dot on the domain name patterns.

RUNNING OTHER COMMANDS

spawn shell_command

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

twist shell_command

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:

in.telnetd : ... : twist PATH=/some/other; exec in.telnetd Warning: in case of UDP services, do not twist to commands that use the standard I/O or the read(2)/write(2) routines to communicate with the client process; UDP requires other I/O primitives.

NETWORK OPTIONS

keepalive

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.

linger number_of_seconds

Specifies how long the kernel will try to deliver not-yet delivered data after the server process closes a connection.

USERNAME LOOKUP

rfc931 [ timeout_in_seconds?

Look up the client user name with the RFC 931 (TAP, IDENT, RFC 1413) protocol. This option is silently ignored in case of services based on transports other than TCP. It requires that the client system runs an RFC 931 (IDENT, etc.)

• compliant daemon, and may cause noticeable delays with

connections from non-UNIX clients. The timeout period is optional. If no timeout is specified a compile-time defined default value is taken.

MISCELLANEOUS

banners /some/directory

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.

umask 022

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.

user nobody

user nobody.kmem

Assume the privileges of the

DIAGNOSTICS

When a syntax error is found in an access control rule, the error is reported to the syslog daemon; further options will be ignored, and service is denied.

SEE ALSO

hosts_access(5), the default access control language

AUTHOR

Wietse Venema (wietse@wzv.win.tue.nl) Department of Mathematics and Computing Science Eindhoven University of Technology Den Dolech 2, P.O. Box 513, 5600 MB Eindhoven, The Netherlands