HOSTS_OPTIONS(5) File Formats Manual HOSTS_OPTIONS(5)
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 ":" characters within options should be protected with a backslash.
An option is of the form "keyword" or "keyword value". Options are processed in the specified order. Some
options are subjected to %<letter> substitutions. For the sake of backwards compatibility with earlier ver‐
sions, an "=" is permitted between keyword and value.
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 exam‐
ple 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 %<letter> expansions
described in the hosts_access(5) manual page. The command is executed with stdin, stdout and stderr
connected to the null device, so that it won´t mess up the conversation with the client host. Example:
spawn (/some/where/safe_finger -l @%h | /usr/ucb/mail root) &
executes, in a background child process, the shell command "safe_finger -l @%h | mail root" after
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) ser‐
vices.
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 car‐
riage-return newline, and %<letter> sequences are expanded (see the hosts_access(5) manual page).
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 %<letter> expansions
and may contain whitespace (but leading and trailing blanks are stripped off).
Warning: many network daemons reset their environment before spawning a login or shell process.
umask 022
options will be ignored, and service is denied.
SEE ALSO
hosts_access(5), the default access control language
AUTHOR
Wietse Venema ([email protected])
Department of Mathematics and Computing Science
Eindhoven University of Technology
Den Dolech 2, P.O. Box 513,
5600 MB Eindhoven, The Netherlands
HOSTS_OPTIONS(5)
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