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HOSTS_OPTIONS(5) 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 remain-
der 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 versions, 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 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 %<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 replacing %h by the name or address of the remote
host.
The example uses the "safe_finger" command instead of the regular "finger"
command, to limit possible damage from data sent by the finger server. The
"safe_finger" command is part of the daemon wrapper package; it is a wrapper
around the regular finger command that filters the data sent by the remote
host.
twist shell_command
Replace the current process by an instance of the specified shell command,
after performing the %<letter> expansions described in the hosts_access(5)
manual page. Stdin, stdout and stderr are connected to the client process.
This option must appear at the end of a rule.
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 connec-
tion 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) proto-
col. This option is silently ignored in case of services based on trans-
ports other than TCP. It requires that the client system runs an RFC 931
(IDENT, etc.) -compliant daemon, and may cause noticeable delays with con-
nections from non-UNIX clients. The timeout period is optional. If no time-
out 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 pro-
cess (for example in.telnetd for the telnet service), and copy its contents
to the client. Newline characters are replaced by carriage-return newline,
and %<letter> sequences are expanded (see the hosts_access(5) manual page).
The tcp wrappers source code distribution provides a sample makefile (Ban-
ners.Makefile) for convenient banner maintenance.
Warning: banners are supported for connection-oriented (TCP) network ser-
vices 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 sub-
jected 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
Like the umask command that is built into the shell. An umask of 022 pre-
vents 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 "nobody" userid (or user "nobody", group
"kmem"). The first form is useful with inetd implementations that run all
services with root privilege. The second form is useful for services that
need special group privileges only.
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 AT wzv.nl)
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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On Apache/1.3.41 (Unix) PHP/5.2.5 mod_perl/1.30 mod_gzip/1.3.26.1a
Under GNU General Public License
2009-01-09 08:57 @38.103.63.58 CrawledBy CCBot/1.0 (+http://www.commoncrawl.org/bot.html)