SOCKS.CONF(5) File Formats Manual SOCKS.CONF(5)
socks.conf - SOCKS clients configuration file
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 coun-
Each line in the file may be up to 1024 characters long. Lines starting with a # are comments. Non-comment lines must be of one of the
deny [*=userlist] dst_addr dst_mask [op dst_port] [: shell_cmd]
direct [*=userlist] dst_addr dst_mask [op dst_port] [: shell_cmd]
sockd [@=serverlist] [*=userlist] dst_addr dst_mask [op dst_port] [: shell_cmd]
A deny line tells the SOCKS clients when to reject a request. A direct lines tells when to use a direct connection. A sockd 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 userlist 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 /. 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 # marks the remainder of the line as comment. Each line in the files may be up
to 1023 characters long. If the *=userlist field is omitted, the line applies to all user-ids.
The dst_addr field specifies either the IP address of a host, a network, or a subnet in the usual dotted form, e.g., 126.96.36.199, or a
doamin name, e.g., internic.net. dst_mask specifies mask for the IP address used in dst_addr. Bits in dst_mask that are set to 0 indicate
the bit positions to be ignored during comparison of IP addresses. So, specifying 255.255.255.255 in dst_mask demands an exact match with
dst_addr, whereas 0.0.0.0 in dst_mask causes a matching with any given destination address regardless of what is specified for dst_addr. If
a domain name is used for dst_addr, the contents of dst_mask 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, xyz.com matches only xyz.comP, while .xyz.com macthes not only xyz.com, but also abc.xyz.com and
this.and.that.xyz.com, among others. The special symbol ALL (which must be entirely in uppercase) matches everything. Domain names are
When using a domain name in dst_addr, you have be very careful in maintaining your DNS setup. See the last few paragraphs in sockd.conf(5).
The op field must be eq, neq, lt, gt, le, or ge, for the condition of equal, not equal, less than, greater than, less than or equal, and
greater than or equal, respectively. The dst_port field can be either a port number, e.g., 23, or the equivalent service name as specified
in file /etc/services, e.g., telnet for port number 23. If this pair is omitted, the line applies to all services.
The serverlist, which may only be used in a sockd 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 SOCKS_SERVER if it
exists, or the name compiled into the SOCKS client program otherwise.
sockd @=188.8.131.52 *=boss,root 184.108.40.206 255.255.255.255 eq telnet
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 desti-
nation IP address must be 220.127.116.11 exactly, and the service requested must be telnet. In that case, connection to host 18.104.22.168
should be done via a SOCKS proxy server on host 22.214.171.124.
Every time a SOCKS client has to make a network connection, it checks the pending request against the file /etc/socks.conf, 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 /etc/socks.conf 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 shell_cmd 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:
%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 %
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.,
deny 0.0.0.0 0.0.0.0 : /usr/ucb/mail -s 'SOCKS: rejected %S from %u to %Z' root
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 spec-
ify either of them in /etc/socks.conf.
You have the option of using the frozen file /etc/socks.fc instead of /etc/socks.conf. The frozen file is produced by make_socksfc 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 /etc/socks.fc first, be sure that you always run make_socksfc every
time after you modify /etc/socks.conf.
SOCKS_SERVER, if defined, specifies the name or IP address of the SOCKS proxy server host to use, overriding the default server compiled
into the programs.
dump_socksfc(8), make_socksfc(8), sockd(8), sockd.conf(5), socks_clients(1), socks.fc(5)
May 6, 1996 SOCKS.CONF(5)