NAME¶
socks.conf - SOCKS clients configuration file
SYNOPSIS¶
/etc/socks.conf
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
# are comments. Non-comment lines must be of one of the three forms:
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.,
129.201.4.0, 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 otherwise case-insentive.
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.
Consider
sockd @=1.2.3.4 *=boss,root 11.12.13.14 255.255.255.255 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 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
/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 specify 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.
ENVIRONMENT¶
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.
SEE ALSO¶
dump_socksfc(8),
make_socksfc(8),
sockd(8),
sockd.conf(5),
socks_clients(1),
socks.fc(5)