2.11BSD/man/cat8/identd.0
IDENTD(8) UNIX Programmer's Manual IDENTD(8)
NAME
identd, in.identd - TCP/IP IDENT protocol server
SYNOPSIS
/usr/libexec/[in.]identd [-i|-w|-b [-t<seconds>] [-u<uid>]
[-g<gid>] [-p<port>] [-a<address>] [-c<charset>]
[-C[<keyfile>]] [-o] [-e] [-l] [-V] [-m] [-N] [-d]
[-F<format>] [kernelfile[kmemfile]]
DESCRIPTION
identd is a server which implements the TCP/IP proposed
standard IDENT user identification protocol as specified in
the RFC 1413 document.
identd operates by looking up specific TCP/IP connections
and returning the user name of the process owning the con-
nection. It can optionally return other information instead
of a user name.
ARGUMENTS
The -i flag, which is the default mode, should be used when
starting the daemon from inetd with the "nowait" option in
the /etc/inetd.conf file. Use of this mode will make inetd
start one identd daemon for each connection request.
The -w flag should be used when starting the daemon from
inetd with the "wait" option in the /etc/inetd.conf file .
This is the prefered mode of operation since that will start
a copy of identd at the first connection request and then
identd will handle subsequent requests without having to do
the nlist lookup in the kernel file for every request as in
the -i mode above. The identd daemon will run either for-
ever, until a bug makes it crash or a timeout, as specified
by the -t flag, occurs.
The -b flag can be used to make the daemon run in standalone
mode without the assistance from inetd. This mode is the
least prefered mode since a bug or any other fatal condition
in the server will make it terminate and it will then have
to be restarted manually. Other than that it has the same
advantage as the -w mode in that it parses the nlist only
once.
The -t<seconds> option is used to specify the timeout limit.
This is the number of seconds a server started with the -w
flag will wait for new connections before terminating. The
server is automatically restarted by inetd whenever a new
connection is requested if it has terminated. A suitable
value for this is 120 (2 minutes), if used. It defaults to
no timeout (i.e. will wait forever, or until a fatal condi-
tion occurs in the server).
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IDENTD(8) UNIX Programmer's Manual IDENTD(8)
The -u<uid> option is used to specify a user id number which
the ident server should switch to after binding itself to
the TCP/IP port if using the -b mode of operation.
The -g<gid> option is used to specify a group id number
which the ident server should switch to after binding itself
to the TCP/IP port if using the -b mode of operation.
The -p<port> option is used to specify an alternative port
number to bind to if using the -b mode of operation. It can
be specified by name or by number. Defaults to the IDENT
port (113).
The -a<address> option is used to specify the local address
to bind the socket to if using the -b mode of operation. Can
only be specified by IP address and not by domain name.
Defaults to the INADDR_ANY address which normally means all
local addresses.
The -V flag makes identd display the version number and then
exit.
The -l flag tells identd to use the System logging daemon
syslogd for logging purposes.
The -o flag tells identd to not reveal the operating system
type it is run on and to instead always return "OTHER".
The -e flag tells identd to always return "UNKNOWN-ERROR"
instead of the "NO-USER" or "INVALID-PORT" errors.
The -c<charset> flags tells identd to add the optional
(according to the IDENT protocol) character set designator
to the reply generated. _c_h_a_r_s_e_t should be a valid character
set as described in the MIME RFC in upper case characters.
The -C[<keyfile>] option tells identd to return encrypted
tokens instead of user names. The local and remote IP
addresses and TCP port numbers, the local user's uid number,
a timestamp, a random number, and a checksum, are all
encrypted using DES with a secret key derived from the first
line of the _k_e_y_f_i_l_e (using des_string_to_key(3)). The
encrypted binary information is then encoded in a base64
string (32 characters in length) and enclosed in square
brackets to produce a token that is transmitted to the
remote client. The encrypted token can later be decrypted
by idecrypt(8). There may not be a space between the -C and
the name of the _k_e_y_f_i_l_e. If the _k_e_y_f_i_l_e is not specified,
it defaults to /etc/identd.key.
The -n flag tells identd to always return user numbers
instead of user names if you wish to keep the user names a
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IDENTD(8) UNIX Programmer's Manual IDENTD(8)
secret. The -N flag makes identd check for a file
".noident" in each homedirectory for a user which the daemon
is about to return the user name for. It that file exists
then the daemon will give the error HIDDEN-USER instead of
the normal USERID response.
-m flag makes identd use a mode of operation that will allow
multiple requests to be processed per session. Each request
is specified one per line and the responses will be returned
one per line. The connection will not be closed until the
connecting part closes it's end of the line. PLEASE NOTE
THAT THIS MODE VIOLATES THE PROTOCOL SPECIFICATION AS IT
CURRENTLY STANDS.
The -d flag enables some debugging code that normally should
NOT be enabled since that breaks the protocol and may reveal
information that should not be available to outsiders.
The -F<format> option makes identd use the specified format
to display info. The allowed format specifiers are:
%u print user name
%U print user number
%g print (primary) group name
%G print (primary) group number
%l print list of all groups by name
%L print list of all groups by number
%p print process ID of running process
%c print command name
%C print command and arguments
The lists of groups (%l, %L) are comma-separated, and start
with the primary group which is not repeated. The %p and the
%c and %C formats are not supported on all architecture
implementations (printing 0 or empty string instead).
Any other characters (preceded by %, and those not preceded
by it) are printed literally. The "default" format is %u,
and you should not use anything else without the -o flag.
Not implemented yet, but on my wish-list are the following:
%w print working (current) directory
%h print home (login, naming) directory
%e print the environment
kernelfile defaults to the normally running kernel file.
kmemfile defaults to the memory space of the normally run-
ning kernel.
UNDOCUMENTED FLAGS
The -v flag enables more verbose output or messages.
(Further occurences of the -v flag make things even more
verbose.) Currently not used: ignored.
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IDENTD(8) UNIX Programmer's Manual IDENTD(8)
The -f<config-file> option causes identd to use the named
config file (instead of the default /etc/identd.conf ?).
Currently not used: ignored, no config files are used.
The -r<indirect_host> option is used in some way (for proxy
queries?).
The -C<keyfile> option is used in some way for DES encryp-
tion.
INSTALLATION
identd is invoked either by the internet server (see
inetd(8C) ) for requests to connect to the IDENT port as
indicated by the /etc/services file (see services(5) ) when
using the -w or -i modes of operation or started manually by
using the -b mode of operation.
EXAMPLES
Assuming the server is located in /usr/etc/in.identd one can
put either:
ident stream tcp wait sys /usr/etc/in.identd in.identd -w
-t120
or:
ident stream tcp nowait sys /usr/etc/in.identd in.identd -i
into the /etc/inetd.conf file. User "sys" should have enough
rights to READ the kernel but NOT to write to it.
To start it using the -b mode of operation one can put a
line like this into the /etc/rc.local file:
/usr/etc/in.identd -b -u2 -g2
This will make it run in the background as user 2, group 2
(user "sys", group "kmem" on SunOS 4.1.1).
NOTES
The username (or UID) returned ought to be the login name.
However it (probably, for most architecture implementations)
is the "real user ID" as stored with the process; there is
no provision for returning the "effective user ID". Thus the
UID returned may be different from the login name for setuid
programs (or those running as root) which done a setuid(3)
call and their children. For example, it may (should?) be
wrong for an incoming ftpd ; and we are probably interested
in the running shell, not the telnetd for an incoming telnet
session. (But of course identd returns info for outgoing
connections, not incoming ones.)
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IDENTD(8) UNIX Programmer's Manual IDENTD(8)
The group or list of groups returned (with the -F option)
are as looked up in the /etc/passwd and /etc/group files,
based on the UID returned. Thus these may not relate well to
the group(s) of the running process for setuid or setgid
programs or their children.
The command names returned with formats %c and %C may be
different, use one or the other or both.
FILES
/etc/identd.conf
This file is as yet un-used, but will eventually con-
tain configuration options for identd
/etc/identd.key
If compiled with -_l_d_e_s this file can be used to specify
a secret key for encrypting replies.
SEE ALSO
authuser(3) , inetd.conf(5) , idecrypt(8)
BUGS
The handling of fatal errors could be better.
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