identd(8)
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IDENTD(8) IDENTD(8)
NAME
identd - TCP/IP IDENT protocol server
SYNOPSIS
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>] [-L<user-
name>] [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 forever, until a bug makes it crash or a time-
out, as specified by the -t flag, occurs.
The -b flag can be used to make the daemon run in stan-
dalone 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 terminat-
ing. The server is automatically restarted by inetd when-
ever 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 condition occurs in the server).
The -u<uid> option is used to specify a user id number
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IDENTD(8) IDENTD(8)
which the ident server should switch to after binding
itself to the TCP/IP port if using the -b mode of opera-
tion.
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 opera-
tion.
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 nor-
mally 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 sys-
tem 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. charset should be a valid charac-
ter set as described in the MIME RFC in upper case charac-
ters.
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 num-
ber, a timestamp, a random number, and a checksum, are all
encrypted using DES with a secret key derived from the
first line of the keyfile (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 keyfile. If the key-
file is not specified, it defaults to /etc/identd.key.
The -n flag tells identd to always return user numbers
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IDENTD(8) IDENTD(8)
instead of user names if you wish to keep the user names a
secret. The -N flag makes identd check for a file
".noident" in each homedirectory for a user which the dae-
mon 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 for-
mat 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 archi-
tecture implementations (printing 0 or empty string
instead).
Any other characters (preceded by %, and those not pre-
ceded 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 follow-
ing:
%w print working (current) directory
%h print home (login, naming) directory
%e print the environment
The -L<user name> option instructs identd to lie brazenly
about the identity of the user in question. You didn't
really intend to trust my assertion about who I was any-
way, right?
This flag provides a way for a site to support services
requiring the ident protocol while providing a standard
answer to all ident queries. All queries to identd will
respond with a host type of `OTHER' and a username of
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IDENTD(8) IDENTD(8)
<user name>.
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. (Fur-
ther occurences of the -v flag make things even more ver-
bose.) Currently not used: ignored.
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 man-
ually by using the -b mode of operation.
EXAMPLES
Assuming the server is located in /usr/libexec/identd one
can put either:
ident stream tcp wait sys /usr/libexec/identd identd -w
-t120
or:
ident stream tcp nowait sys /usr/libexec/identd 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/libexec/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
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IDENTD(8) IDENTD(8)
implementations) is the "real user ID" as stored with the
process; there is no provision for returning the "effec-
tive 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.)
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 set-
gid 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
contain configuration options for identd
/etc/identd.key
If compiled with -ldes this file can be used to
specify a secret key for encrypting replies.
SEE ALSO
inetd.conf(5)
BUGS
The handling of fatal errors could be better.
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