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.TH SOCKS.CONF 5 "May 6, 1996"
.SH NAME
.nf
socks.conf \- SOCKS clients configuration file
.fi
.SH SYNOPSIS
/etc/socks.conf
.SH DESCRIPTION
All SOCKS client programs use this file to determine whether to
use direct or proxy connection to a given destination host, and
to exert access control based on the destination host, the requested
service (port number on the destination host), and the effective user-id
of the requesting local user. If this file is absent, SOCKS clients will
only try direct connections, making them behave like their regular counterparts.
Each line in the file may be up to 1024 characters long.
Lines starting with a \fB#\fP are comments. Non-comment lines must be
of one of the three forms:
.nf
.+1
\fBdeny \fI[\fB*=\fIuserlist] dst_addr dst_mask [op dst_port] [: shell_cmd]\fP
\fBdirect \fI[\fB*=\fIuserlist] dst_addr dst_mask [op dst_port] [: shell_cmd]\fP
\fBsockd \fI[\fB@=\fIserverlist] [\fB*=\fIuserlist] dst_addr dst_mask [op dst_port] [: shell_cmd]\fR
.-1
.fi
A \fBdeny\fP line tells the SOCKS clients when to reject a request.
A \fBdirect\fR lines tells when to use a direct connection. A \fBsockd\fR
line indicates when to use a proxy connection and, optionally, which
SOCKS proxy server or servers it should try.
Spaces and tabs separate the fields. Fields enclosed in square brackets
are optional.
The \fIuserlist\fR field, when present, consists of
one or more user-ids or filenames, with comma as separator. No spaces
or tabs are allowed in the list. The user-ids should be ids of users on the
local host, not those on the destination host or the SOCKS server host.
The filenames must be full pathnames with the leading \fB/\fP. Inside
the specified files, user-ids may be listed one or several per line,
with any combination of blanks, tabs, and commas as separators. The
appearance of \fB#\fP marks the remainder of the line as comment. Each
line in the files may be up to 1023 characters long.
If the \fB*=\fIuserlist\fR field is omitted, the line applies to all user-ids.
The \fIdst_addr\fR field specifies either the IP address of a host,
a network, or a subnet in the usual dotted form, e.g., \fB129.201.4.0\fP,
or a doamin name, e.g., \fBinternic.net\fP. \fIdst_mask\fR specifies
mask for the IP address used in \fIdst_addr\fR.
Bits in \fIdst_mask\fP that are set to 0 indicate the
bit positions to be ignored during comparison of IP addresses. So,
specifying 255.255.255.255 in \fIdst_mask\fP demands an exact match
with \fIdst_addr\fP, whereas 0.0.0.0 in \fIdst_mask\fP causes a
matching with any given destination address regardless of what is
specified for \fIdst_addr\fP. If a domain name is used for
\fIdst_addr\fR, the contents of \fIdst_mask\fR are
ignored, though it must still be supplied (simply use 0.0.0.0).
If the domain name starts with a period, it specifies a zone and
matches all domain names within that zone, otherwise it matches
only the domain name itself. For example, \fBxyz.com\fP matches
only xyz.comP, while \fB.xyz.com\fP macthes not only xyz.com,
but also abc.xyz.com and this.and.that.xyz.com, among others.
The special symbol \fBALL\fP (which must be entirely in uppercase)
matches everything. Domain names are otherwise case-insentive.
When using a domain name in \fIdst_addr\fP, you have be very careful
in maintaining your DNS setup. See the last few paragraphs in
\fIsockd.conf\fP(5).
The \fIop\fP field must be \fBeq\fR, \fBneq\fR, \fBlt\fR, \fBgt\fR,
\fBle\fR, or \fBge\fR, for the condition of equal, not equal, less than,
greater than, less than or equal, and greater than or equal, respectively.
The \fIdst_port\fP field can be either a port number, e.g., 23, or the
equivalent service name as specified in file /etc/services, e.g., \fBtelnet\fR
for port number 23. If this pair is omitted, the line applies to all
services.
The \fIserverlist\fP, which may only be used in a \fBsockd\fR line,
consists of one or more SOCKS proxy servers, which the client program should
try to use (in the indicated order) for establishing a proxy connection.
Only commas can be used as separator, no spaces
or tabs are allowed in the list. Domain names of the servers may be used
in the list, though it is probably more prudent to specify IP addresses.
If this field is omitted, the client program will use the
default SOCKS proxy server, which is determined by the environment variable
\fBSOCKS_SERVER\fR if it exists, or the name compiled into the SOCKS client
program otherwise.
Consider
.nf
.+1
sockd @=1.2.3.4 *=boss,root 11.12.13.14 255.255.255.255 eq telnet
.-1
.fi
To match the condition indicated in this line, a request must come from
a local user whose effective id is either boss or root, the destination
IP address must be 11.12.13.14 exactly, and the service requested must
be telnet. In that case, connection to host 11.12.13.14 should be done
via a SOCKS proxy server on host 1.2.3.4.
Every time a SOCKS client has to make a network connection, it checks
the pending request against the file \fB/etc/socks.conf\fR, one line at
a time. Once it finds a line with conditions that are matched by the
request, the action specified on that line is taken. The remaining
lines of file \fB/etc/socks.conf\fR are skipped. So the order of the
lines in the file is extremely important; switch two lines and you may
have entirely different results. If no matching line
is found throughout the file, the request is denied.
The \fIshell_cmd\fR field specifies a command string that is executed
when the conditions on that line are satisfied. The following substitutions
occur before the string is presented to the Borne shell for execution:
.nf
.in +1
%A -- replaced by the client host's domainname if known, by its IP address otherwise
%a -- replaced by the client host's IP address
%c -- replaced by "connect" or "bind"
%p -- replaced by the process id of the client program
%S -- replaced by the service name (e.g., ftp) if known, by the destination port number otherwise
%s -- replaced by the destination port number
%U -- replaced by the user-id at login
%u -- replaced by the effective user-id
%Z -- replaced by the destination host's domainname if known, by its IP address otherwise
%z -- replaced by the destination host's IP address
%% -- replaced by a single %
.fi
.in -1
Several shell commands can be strung together in the usual way with `|',
`;', etc.
Although there is an implied 'deny all' at the end of the control file,
you may supply one explicitly so as to take some specific action when requests
are so rejected, e.g.,
.nf
.in +1
deny 0.0.0.0 0.0.0.0 : /usr/ucb/mail -s 'SOCKS: rejected %S from %u to %Z' root
.fi
.in -1
Unlike the previous version, connection to address 127.0.0.1 or 0.0.0.0
is always done directly to localhost, so there is no need to specify
either of them in \fB/etc/socks.conf\fP.
You have the option of using the frozen file \fB/etc/socks.fc\fP
instead of \fB/etc/socks.conf\fP. The frozen file is produced by
\fImake_socksfc\fR and is essentially the memory image of the parsed
configuration file. using it can reduced the start-up delay of SOCKS
client applications since no parsing is needed. Because SOCKS client
applications always look for \fB/etc/socks.fc\fP first, be sure that
you always run \fImake_socksfc\fR every time after you modify
\fB/etc/socks.conf\fP.
.SH ENVIRONMENT
\fBSOCKS_SERVER\fR, if defined, specifies the name or IP address of the
SOCKS proxy server host to use, overriding the default server
compiled into the programs.
.SH SEE ALSO
\fIdump_socksfc\fP(8), \fImake_socksfc\fP(8),
\fIsockd\fP(8), \fIsockd.conf\fP(5),
\fIsocks_clients\fP(1), \fIsocks.fc\fP(5)
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