IKSD - The Internet Kermit Service Daemon
IKSD SYSTEM ADMINISTRATOR'S GUIDE FOR UNIX
The Kermit Project
Columbia University
http://www.columbia.edu/kermit/
- As of:
-
C-Kermit 8.0, 12 Dec 2001
- Most Recent Content:
-
23 March 2003
- Most Recent Update:
-
31 July 2021
(FTP links changed to HTTP)
The Internet Kermit Service Daemon (IKSD) is C-Kermit 7.0 or later, started
in a special way. At this writing, only the UNIX version of C-Kermit
can act as IKSD, but IKSD will also be available soon in the Windows
version, and can be added to the VMS, VOS, and other versions if there is
sufficient demand. The Internet Kermit Service is specified in
RFC2839 and
RFC2840.
1. Why IKSD?
2. System Configuration
3. Compile-Time Configuration Options
4. Runtime Configuration Options
4.1. Command-Line Options
4.2. System Logging
4.3. The IKSD Log File
4.4. IKSD Configuration File
4.5. Initialization File
5. Access to Services
5.1. Automatic Settings
5.2. Authentication
5.3. The DISABLE Command
5.4. Shell Access
5.5. Anonymous Users
5.6. Management Information
6. Open Issues
6.1. Connection Establishment
6.2. Shell Access
6.3. External and/or non-Kermit Protocols
6.4. Additional Administrative Controls
6.5. Known Bugs
7. Monitoring
7.1. Database Record Format
7.2. The Display Module
7.3. Database Management
8. Testing
Why run an Internet Kermit Service Daemon when you are already running
an FTP server?
- Like FTP, Kermit provides a service that can be accessed from many
different platforms with a consistent set of commands, but unlike FTP,
these commands include programming constructions such as variables,
arrays, looping and selection mechanisms, and local and remote procedure
calls, thus allowing file transfer and management operations of arbitrary
complexity to be easily automated.
- Like FTP, Kermit provides both text- and binary-mode data transfer, as
well as file management capabilities. But Kermit also offers numerous
features lacking from FTP, such as:
- Unlike FTP, Kermit supports
atomic file movement, in which the source
file can be deleted (or renamed, or moved) when and only when it has been
transferred successfully, as part of the transfer operation itself.
- Unlike most FTP implementations, Kermit supports
recovery of interrupted
transfers from the point of failure. You can even use it to recover
interrupted FTP transfers when FTP itself does not offer this option.
- Unlike standard FTP, Kermit can transfer data through firewalls or
proxies or NATs on a single well-known port (unless the TCP port for the
connection has been explicitly filtered).
- Unlike FTP, Kermit can transfer data across a combination of transports
(e.g. dial-up to a terminal server and thence to an Internet host).
- Authentication and data transfer can take place over
secure connections
(mutually authenticated and encrypted) using established Telnet
authentication and encryption options.
- Unlike traditional Kermit use over Telnet, anonymous access is possible,
and the considerable overhead of the intervening Telnet server and
pseudoterminal service is eliminated.
- Unlike the FTP daemon (ftpd), the IKSD can be monitored in real time
by the system administrator (see Section 7).
A prototype IKSD is available for public access at:
kermit.columbia.edu port 1649
This service is based in part on a new Telnet Kermit Option described in
RFC2839
RFC2840
WARNING: Do
not attempt to install a pre-7.0 version of C-Kermit as an
IKSD. Earlier versions do not perform the necessary authentication and
security functions, and therefore will leave your system wide open to
anonymous root access. (Don't worry, the installation procedure described
here, if you follow it, and the interface to IKSD, prevent you from starting
an earlier version of C-Kermit as an IKSD, since it lacks the needed
command-line options and will halt with a usage message if you try to use
them.)
Directory organization, file system, naming conventions, and other
administrative details vary from system to system and site to site, so
specific instructions can not be given here. In general, however, the steps
are:
- The C-Kermit executable should be copied to the directory
that is normally used for launching Internet services, and renamed to "iksd".
Normally the owner and group should be root and the permission 0750.
- The following entry should be added to the Internet services file,
normally /etc/services:
kermit 1649/tcp
- An entry must be made in the inetd configuration file, normally
/etc/inetd.conf. See your system-specific documentation for the
name, location, and format of this file, e.g. "man inetd" and
"man inetd.conf". Typical example:
kermit stream tcp nowait root iksd -A other-iksd-options
Or, with TCP wrappers:
kermit stream tcp nowait root tcpd iksd -A other-iksd-options
Include full pathnames for tcpd and iksd if required. See
Section 4 for iksd-options.
NOTE: Different platforms might require different syntax, e.g.:
kermit stream tcp nowait root /usr/sbin/iksd iksd -A other-iksd-options
- When using TCP wrappers, make the appropriate entries in its
configuration file(s), such as /etc/hosts.allow and
/etc/hosts.deny.
See the TCP wrappers documentation for further info.
- Make any required hard or soft links to the iksd executable.
- If desired, create an IKSD configuration file
(/etc/iksd.conf by default).
This setup allows multiple simultaneous IKSD sessions. A fresh IKSD process
is started for each session, and disappears when IKSD exits, automatically
closing the session and the connection.
To kill a particular instance of IKSD, find its pid with "ps ax | grep
iksd" (or the equivalent command to list all processes) and then
"kill -9 pid" (as root).
To update the IKSD program, simply replace the executable in the "launch"
directory ((a) above).
To discontinue IKSD service quickly, delete the iksd executable, or (to avoid
unwanted console logging) replace it with (say) /bin/false.
You can use any C-Kermit configuration as an IKSD, ranging from a fully
configured version, to a special IKSD-Only version, to any of the various
"stripped-down" versions, as described in the C-Kermit Configuration Guide
(
ckccfg.txt)
and/or Installation Instructions
(
ckuins.txt).
The following compile-time options are specific to or of special relevance
to the IKSD:
- TNCODE - Required for IKS.
- Include Telnet protocol code, even if networking code is not included.
Defined by default if TCPSOCKET defined, otherwise must be defined
explicitly.
- IKS_OPTION - Required for IKS.
- Include code for the new Internet Kermit Service Option.
Currently defined automatically if TNCODE is defined.
- CK_LOGIN - Required for IKS.
- Include user authentication code. Defined automatically for UNIX unless
NOLOGIN defined.
- CK_PAM
- The IKS is to be compiled to use PAM (Pluggable Authentication Modules)
to authenticate the user for interactive logins instead of Unix password
files. The default PAM service type for IKSD is "kermit". Might also
require -lpam.
- PAM_SERVICE_TYPE
- If CK_PAM is defined and you wish to use a service type other than
"kermit" you can define PAM_SERVICE_TYPE to equal the string you
wish to use.
- CK_SHADOW
- If your host utilizes the shadow password system for storing user
passwords the IKS must be compiled with support for shadow passwords.
This might also require some additional libraries added the LIBS
clause, such as -lgen, for loading the getspnam() routine.
- CKSYSLOG
- Include code for making syslog entries. This symbol is defined
automatically if (a) CK_LOGIN is defined; (b) UNIX is defined; and (c)
NOSYSLOG is not defined.
- CKWTMP
- Include code for making wtmp log entries. This symbol is defined
automatically if (a) CK_LOGIN is defined; (b) UNIX is defined; and (c)
NOWTMP is not defined.
- WTMPFILE
- String containing pathname of the default wtmp logfile. If not specified,
a default is supplied, currently /var/log/wtmp on Linux and
/usr/adm/wtmp elsewhere. The wtmp file can also be specified at
runtime; see next section.
- CK_CURSES
- Need not be defined in an IKSD-only build, since curses is used only
in local mode, and the IKSD is always in remote mode, plus the fact that
curses initialization can cause spurious error messages in IKSD since it
might not have a terminal type (TERM variable) in its environment.
- NOLOCAL
- This may be defined to exclude all code relating to the making of
both serial and network connections from the C-Kermit/IKSD executable.
This code is presently not needed, and is never used, in the IKSD.
Compiling it out reduces the size of the executable and eliminates any
possibility that a loophole could be exploited to use the IKSD as a
relay.
- NOPUSH
- This symbol may be defined to exclude all code that is used to access
local shell or system functions, such as the RUN (!) command, the server
end of the REMOTE HOST command, file-transfer pipes and filters, etc.
Note that such code is disabled at runtime in the IKS anyway; compiling
it out completely reduces the size of the executable and the risk of
loopholes.
- NOICP
- Disables the interactive command parser as well as long-form command-line
options (Section 4.1). In this configuration, the IKS
runs only in Kermit Server mode, and the size of the executable is reduced
dramatically. WARNING: NOICP also inhibits extended command-line options (the
ones that start with "--"), since these share the same parsing
routines as the interactive parser.
- NOSPL
- Disables the script programming language (INPUT, OUTPUT, FOR, WHILE,
IF, SWITCH, macros, variables, etc) without disabling the interactive
command parser.
- NOGETUSERSHELL
- Add this if the link steps fails because it can't resolve
getusershell() and/or endusershell(). Normally, IKSD will
refuse a login if the user's login shell is not one of those returned by
getusershell() (normally, getusershell() simply lists the shells listed in
/etc/shells, but we can't depend on this). Thus if your site
"invalidates" user IDs by setting their login shell to something that is not
really a shell (like /etc/nologin), but does not have a
getusershell() function, IKSD will still let such users log in unless
(a) you put them in the forbidden users file (see Section 4.1), or (b) add some code to ckufio.c to
check for whatever invalid or valid shells might apply at your site.
- NOIKSD
- This defines the symbols NOLOGIN, NOSYSLOG, NOWTMP, NOPRINTFSUBST, which
in turn prevent the definition of symbols (CK_LOGIN, CKSYSLOG, etc) that
cause IKSD-specific code to be included.
- CK_SYSINI
- CK_DSYSINI
- System-wide initialization file; see
Section 4.4.
- IKSD
- Is defined automatically if NOIKSD is not defined.
- IKSDCONF
- The name of the IKSD configuration file. In UNIX this is
"/etc/iksd.conf" by default; elsewhere "iksd.cfg".
In an IKSD-only build, you should omit the termcap/termlib and (n)curses
libraries, and set up the link step to make sure the IKSD is linked with
the same user authorization libraries used by your local login program.
Here is a sample for SunOS 4.1.3 at a particular site:
sunos41giks:
@echo Making C-Kermit $(CKVER) for SunOS 4.1 with gcc for IKS...
$(MAKE) wermit "CC= gcc" "CC2= gcc" \
"CFLAGS= -O -DSUNOS41 -DNDGPWNAM \
-DTNCODE -DNOLOCAL -DNOPUSH $(KFLAGS)" \
"LIBS= -L/usr/local/lib -lpwent -lcrypt"
in which:
- -DNOLOCAL excludes all code that is used to make connections.
- -DNOPUSH excludes all code that accesses local system shells and commands.
- -DTNCODE includes Telnet protocol code even though -DNOLOCAL is included.
At sites that use shadow passwords, you'll need to add -DCK_SHADOW to CFLAGS
and perhaps -lgen to LIBS.
Also note that the crypt() function, which is used for verifying
passwords, is normally found in libc, but on some platforms it has been broken
out into a separate library, such as -lcrypt, and in that case must be
included in the LIBS clause.
For PAM installations, here's an example /etc/pam.d/kermit file that
uses EPS password files for user authentication and the standard unix modules
for account and session management:
auth required /lib/security/pam_eps_auth.so
password required /lib/security/pam_eps_passwd.so
account required /lib/security/pam_unix_acct.so
session required /lib/security/pam_unix_session.so
Kerberos IV, Kerberos V, SRP, and TLS
can also be selected at build time if you have the appropriate
libraries and header files installed on your system. See the
Kermit Security
Reference for further details.
For a build that excludes all IKSD functions, it is normally sufficient
to add NOIKSD to the CFLAGS, e.g.:
make aix41 KFLAGS=-DNOIKSD
The IKSD can be configured at runtime with command-line options or by an
initialization file or other auxiliary file(s), in any combination.
The SHOW IKSD command lists the IKSD-relevant parameters and their
values.
To start C-Kermit as an Internet Kermit Service Daemon, include the
'
-A' command-line option. This option not only configures C-Kermit
as an IKSD, but it also ensures that you are running a version of C-Kermit
that can do this, i.e. C-Kermit 7.0 or later built with all the necessary
compile-time options (
Section 3). If either of these
conditions does not apply, the '
-A' option will be invalid and the
Kermit program will halt immediately.
In addition to -A and the command-line options described in
Using C-Kermit
(2nd Edition), plus any other new ones described in the
C-Kermit 7.0
Update Notes and
C-Kermit 8.0
Update Notes, a
selection of new long-form options apply specifically to the IKSD. Long-form
options work as follows:
- All long-form options must begin with "--" (two hyphens) or
"-+". If the option begins with "--" it is executed before
or after the C-Kermit initialization file, according to its internal keyword
flags. If it begins with "-+", it is executed before the init file,
regardless of the keyword flags. There is no way to force an argument to be
executed after the init file if it has the CM_PRE bit set (see table below).
- No spaces are allowed in the keyword.
- If an operand contains spaces, it (or the entire option) must be quoted
according to the rules of the shell from which Kermit is invoked.
- Case doesn't matter in the option keyword (unlike with regular
single-letter options).
- If an operand is required, it must be included. If no operand is
required, no operand must be included.
- The operand follows the keyword, separated by a colon (:) or equal
sign (=). There are no spaces between the separator and the keyword
or operand.
- Long-form option names may be abbreviated according to the same rules as
interactive keywords.
- On/Off operands can be On, Off, Yes, No, True, False, 0, 1, or OK (case
of letters does not matter).
- Long-form options are available only when the interactive command parser
is built-in (i.e. not NOICP).
The new long-form options are:
Option Values Default CM_PRE Effect
--anonymous on/off on yes anonymous login allowed
--bannerfile filename (none) no greeting message
-+cdfile filelist (see below) no CD message filename
-+cdmessage on/off on no CD messages on/off
-+cdmsg on/off on no synonym for cdmessage
--help (none) (n/a/) no list available --options
--helpfile filename (none) no custom text for HELP command
--initfile filename /.kermrc yes Init file for anonymous users
--nointerrupt (none) (see below) yes Disables SIGINT and SIGTSTP
--permissions octalnum 0040 yes anonymous upload permissions
--perms octalnum 0040 yes synonym for permissions
--root directory /pub/ftp yes root for anonymous users
--syslog number 3 yes level of syslogging
--timeout number 300 yes time limit for login
--userfile filename /etc/ftpusers yes forbidden local users list
--wtmplog on/off on yes wtmp logging on/off
--wtmpfile filename (see below) yes pathname of wtmp logfile
--xferlog on/off off yes use an ftpd-logfile
--xferfile filename (see below) yes pathname of ftpd-like logfile
Note: in all options that take a filename, except --cdfile,
relative filenames or filenames that start with ~ are expanded to
full pathnames.
In more detail:
- --nointerrupts
- Disables keyboard interrupts that are normally enabled. In IKSD, when it
is in interactive prompting state, commands can normally be interrupted
with Ctrl-C. Suspending (normally via Ctrl-Z) is always disabled in IKSD.
- --help
- Lists the extended command-line options that are available in your version
of C-Kermit. If any options seem to be missing, that is because your
copy of C-Kermit was built with compile-time options to deselect them.
- --helpfile:filename
- Specifies the name of a file to be displayed if the user types HELP
(not followed by a specific command or topic), in place of the built-in
top-level help text. The file need not fit on one screen; more-prompting
is used if the file is more than one screen long if COMMAND MORE-PROMPTING
is ON, as it is by default.
- --anonymous:{on,off}
- Whether anonymous logins are allowed. By default they are allowed, so
this option need be included only to disallow them (or for clarity, to
emphasize that they are allowed). Anonymous login occurs when the username
"anonymous" or "ftp" is given, with any password (as with ftpd).
- --timeout:number
- This sets a limit (in seconds) on the amount of time the client has to log
in once the connection is made. If successful login does not occur within
the given number of seconds, the connection is closed. The default timeout
is 300 seconds (5 minutes). A value of 0 or less indicates there is to be
no limit.
- --bannerfile:filename
- The name of a file containing a message to be printed after the user logs
in, in place of the normal message (Copyright notice, "Type HELP or ? for
help", "Default transfer mode is...", etc).
- --permissions:octalnum
- The permissions given to any file that is uploaded by an anonymous user.
0040 is the default and recommended value. The default permits only
group-read access, and therefore prevents anonymous users from uploading
files (e.g. pirated software) to be downloaded by other anonymous users.
Synonym: --perms.
- --initfile:filename
- The initialization file to be executed for anonymous logins. By default
it is /.kermrc, where "/" is the root of the chroot'd file system. Any
filename that you specify here must be specified in the notation of the
the chroot'd file system. This option is independent of the '-y' option
(alternative init file), which applies only to real users.
- --cdmessage:{on,off,0,1,2}
- For use in the Server-Side Server configuration; whenever the client
tells the server to change directory, the server sends the contents of a
"read me" file to the client's screen. This feature is On by default,
and operates only in client/server mode when ON or 1. If set to 2 or
higher, it also operates when the CD command is given at the IKSD> prompt.
Synonym: --cdmsg.
- --cdfile:filename (or list)
- When cdmessage is on, this is the name of the "read me" file to be sent.
Normally you would specify a relative (not absolute) name, since the file
is opened using the literal name you specified, after changing to the new
directory. Example:
--cdfile:READ.ME
You can also give a list of up to 8 filenames by (a) enclosing each
filename in braces, and (b) enclosing the entire list in braces. Example:
--cdfile:{{./.readme}{READ.ME}{aaareadme.txt}{README}{read-this-first}}
When a list is given, it is searched from left to right and the first
file found is displayed. The default list for UNIX is:
{{./.readme}{README.TXT}{READ.ME}}
- --database:{on,off}
- Whether an active-sessions database should be kept. On by default.
If "on", but --dbfile is not specified, /var/log/iksd.db
is used.
- --dbfile:filename
- Use this option to specify an iksd database file name. If you include
this option, it implies .
- --syslog:number or {on,off}
- Whether and what level of syslog entries should be made. A level of 0
(or "off" or "false" or "no") means no syslogging. A level of "on" (or
"yes" or "true") invokes the default syslogging level. To choose a
non-default level of syslogging, specify a number (see
Section 4.2).
- --wtmplog:{on,off}
- Whether wtmp log entries should be made. On by default. An entry is made
when the user logs in and when the session is closed. The "tty name" field
is given as "iks_xxxx", where xxxx is the process ID (pid) of the IKSD.
Thus IKSD session history can be monitored via "last | grep iks_".
Anonymous logins are shown with a user ID of "ftp".
- --wtmpfile:filename
- The default wtmp log file is /var/log/wtmp in Linux, and
/usr/adm/wtmp elsewhere. In case your system's wtmp log file does
not match the default, use this option to specify the appropriate filename.
- --userfile:filename
- This file contains a list of local usernames that are to be denied access
to Internet Kermit Service. The default is /etc/ftpusers. This can
be the same file that is used by wuftpd, and the syntax is the same: one
username per line; lines starting with "#" are ignored. Use this option to
specify the name of a different forbidden-user file, or use
--userfile:/dev/null to disable this feature in case there is a
/etc/ftpusers file but you don't want to use it.
- --xferlog:{on,off}
- Whether a wu-ftpd-like log should be kept. Off by default. If "on", but
--xferfile is not specified, /var/log/iksd.log is used.
This log is explained in Section 4.3.
- --xferfile:filename
- Use this option to specify an iksd log file name. If you include this
option, it implies --xferlog:on.
- --database:{on,off}
- Whether an active-sessions database should be kept. On by default.
If "on", but --dbfile is not specified, /var/log/iksd.db is
used.
- --dbfile:filename
- Use this option to specify an iksd database file name. If you include
this option, it implies --database:on.
Some of the traditional options have special significance in the IKS, e.g.:
- -x (server mode)
- If this option is included on the IKSD command line, the Client Side Server
configuration is disabled, and the user will not get a Username: or
Password: prompt, and will not be able to access the IKSD command prompt.
A FINISH command sent to the IKSD will log it out and close the
connection, rather than returning it to its prompt.
- -y filename
- Execute "filename" rather than the normal initialization file for real
users; this option does not apply to anonymous users.
- -Y (no init file)
- Do not execute an initialization file, even if a real user is logging in.
Examples:
- kermit -A
- Starts the Internet Kermit Server with all defaults in effect.
- iksd
- Equivalent to "kermit -A".
If the binary is invoked as "iksd" (e.g. through a symlink)
rather than "kermit", the -A option is not necessary.
- iksd --syslog:5
- As above, but with the highest level of syslogging
(Section 4.2).
- iksd --anonymous:off --cdfile:READ.ME
- Starts the IKSD with anonymous access forbidden and changes the name of
CD message file from the default list to READ.ME.
- iksd -x --anonym:no --cdf:READ.ME
- As above, but forces the IKSD to operate only in Kermit server mode,
thus preventing user access to the IKSD command prompt. Also illustrates
abbreviation of long-form option keywords and use of "no" as a synonym
for "off".
Bad syntax in an extended command-line option causes immediate termination
with the message "Extended option error", and an exit status code of 1.
Brief help about command line options may be obtained at the C-Kermit prompt
with "help options", and for extended options with "help extended-options".
You can prototype the IKSD command line by including any desired extended
options, but omitting the -A option, and then when you get the C-Kermit>
prompt, use "show extended-options" to check the parsing of the options you
have included. Example:
$ kermit --anonymous:ok --root:/tmp --userfile:/etc/badusers
(/users/olga/) C-Kermit>show extended-options
--bannerfile=(null)
--cdfile:./.readme
--cdmessage:0
--syslog:3
--wtmplog:1
--wtmpfile=(null)
--anonymous:1
--permission:0040
--initfile:(null)
--userfile:/etc/badusers
--root:/tmp
--xferlog=0
--xferfile=(null)
--timeout:300
(/users/olga) C-Kermit>
Note that this only shows the values that were given as arguments to the
extended options, or their default values, if they have any, but it does
not show values that will be computed dynamically at runtime in the absence
of a command-line value. For example, --wtmplog:1 and
--wtmpfile:(null)
mean that an appropriate default will be supplied for the wtmp logfile name
at runtime.
Also note that SHOW EXTENDED-OPTIONS does not show the IKSD-specific options
when this command given at the IKSD prompt by the user. Thus this command
is useful only as a prototyping tool. (And as noted elsewhere, the IKSD
command-line argument vector is also inaccessible to the IKSD user via other
methods such as the \&@[] array.)
System logging in UNIX is via the standard
syslog() facility ("man
syslog" and/or "man syslogd" for further info).
All IKSD entries (except debugging, see below) appear in the daemon log, as
defined in the syslog.conf file with a tag of "iksd" and the process ID (pid)
of the IKSD process, and therefore can be extracted by grepping for "iksd".
The system logging levels are:
0 = no logging
1 = Login/out, failed login attempts, failed Kerberos (etc) authentication
2 = Dialing out (does not apply to IKSD)
3 = Making any kinds of connections (does not apply to IKSD)
4 = Creating / receiving / deleting / renaming / copying files
5 = Sending / typing / reading / transmitting files
6 = All top-level commands and all server commands sent to iksd
7 = Commands executed from macros and command files
8 = Debug
Each level includes all the levels beneath it (except 0 is not included if
the logging level is greater than 0).
The default logging level is 5, and is used if the --syslog: option is not
included on the command line, or if is given with an affirmative keyword
(yes, true, on, ok) rather than a number. If you specify a number higher than
the maximum, it is the same as specifying the maximum.
Syslog entries are at LOG_INFO priority, except for refused logins, which
are at LOG_NOTICE priority, and failed Telnet-level authentication (such as
Kerberos), which are at LOG_ERR priority.
Note that if C-Kermit is built with -DSYSLOGLEVEL=n (where n is
a number) on the cc command line, this turns on syslogging and hardwires it to
the given level for all users. See
http://www.columbia.edu/kermit/ftp/f/ckuins.txt
for further info.
- WARNING
- Debug level produces VOLUMINOUS amounts of information -- it is
equivalent to (in fact, it is) C-Kermit's debug log. Furthermore,
there is a good possibility it will contain sensitive information such as
clear-text passwords. Debug records are written to the syslog DEBUG facility,
as defined (or not defined) in syslog.conf. If you use this level of logging,
make sure that the logfile defined for "daemon.debug" is secured from the
public, and that there is plenty of space for it.
- ANOTHER WARNING
- In some UNIX systems, syslogging does not work once a
chroot() has occurred, which is done by iksd just as it is by ftpd for
anonymous users, to restrict them to the /pub/ftp (or other desired) directory
tree. At present, SunOS and Linux are known to have this deficiency and there
probably are many others. THERE IS NO SYSLOGGING FOR ANONYMOUS USERS on these
systems. The only way to log the activities of anonymous users on such
systems is to specify a transfer iksd log on the command line
(Sections 4.1 and 4.3).
The transfer log is disabled by default; it must be enabled on the command
line (
Section 4.1).
The transfer log has the same format as the wu-ftpd log, and so all the same
scripts can be used to process it, collect statistics, etc. In fact, you
can even have ftpd and iksd share the same log, in which case records will
be intermixed.
The Transfer log can also be used in regular user-mode C-Kermit sessions.
The first field is fixed-length and contains spaces; subsequent fields are
variable length, contain no spaces, and are separated by one or more spaces.
The fields are:
- Timestamp
- This is an asctime-style timestamp, example: "Wed Sep 16 20:19:05 1998"
It is always exactly 24 characters long, and the subfields are always in
fixed positions.
- Elapsed time
- The whole number of seconds required to transfer the file, as a string
of decimal digits, e.g. "24".
- Connection
- In IKSD, the IP hostname or address of the client. For user-mode C-Kermit
transfers, The name of the network host to which C-Kermit is connected, or
the name of the serial device through which it has dialed (or has a direct
connection), or "/dev/tty" for transfers in remote mode.
- Bytes transferred
- The number of bytes transferred, decimal digits, e.g. "1537904".
- Filename
- The full pathname of the file that was transferred, e.g.
"/pub/ftp/kermit/a/README.TXT". If the filename contains any spaces
or control characters, each such character is replaced by an underscore ('_')
character.
- Mode
- The letter 'b' if the file was transferred in binary mode, or 'a'
if it was transferred in text (ASCII) mode.
- Options
- For compatibility with the wuftpd log. This field always contains an
underscore ('_') character.
- Direction
- The letter 'o' if the file was transferred Out, and 'i' if the file was
transferred In.
- User class
- The letter 'r' for real users, or 'a' for anonymous users.
- User identification
- The user ID of a real user, or the password given by an anonymous user.
- Server identification
- The string "iks" (Internet Kermit Server), or if C-Kermit is running
in user mode, "kermit". This distinguishes a Kermit transfer log
record from a WU-FTPD record, which contains "ftp" in this field.
- Authentication class
- The digit '1' if we know the user's ID on the client system,
otherwise '0'. Currently, always '0'.
- Authenticated user
- If the authentication class is '1', this is the user's ID on the client
system. Otherwise it is an asterisk ('*'). Currently it is always an
asterisk.
The IKSD configuration file is a place to put commands that should always
be executed for every client, real or anonymous.
When C-Kermit is started as IKSD, it always begins by reading the IKSD
configuration file, if any. By default this is /etc/iksd.conf
(you may change the definition at compile time by adding
-DIKSDCONF=\"filename\" to
CFLAGS). This file contains ordinary C-Kermit commands. Normally these
would be SET or DISABLE commands. In case any commands in this file write to
standard output, remember that IKSD's standard output is the connection to
the client. For more ideas about what can go in the iksd.conf file,
read the next section -- the difference is that when you put commands in
the iksd.conf file, they apply not only to anonymous users, but to real
users too. So, for example, if you want to disable uploads for all users,
you could put DISABLE SEND in the iksd.conf file, whereas if you wanted to
disable them only for anonymous users, you would put this command in the
anonymous-user initialization file.
The IKSD configuration file is executed before the user logs in (or is
otherwise authenticated), before the C-Kermit initialization file, and before
any extended-format command line options that start with "--", but
after any that are marked CM_PRE in the table in Section
4.1, or that start with "-+". Since execution occurs before
login, the \v(user) variable is meaningless here.
When a real user logs in to the IKSD, the C-Kermit initialization file is
executed in the normal manner, depending on the compile-time configuration of
the IKSD. Normally, the user's own .kermrc file is executed, and this, in
turn, executes the user's customization file,
.mykermrc. If the IKSD
was built with the CK_SYSINI or CK_DSYSINI compile-time options (described in
ckccfg.txt),
a single, shared system-wide initialization file is executed
instead; this may, in turn, execute a customization file out of the user's
home directory. You may override C-Kermit's automatic selection of
initialization with the regular C-Kermit
-y or
-Y options on
the IKSD command line, described in the C-Kermit manual.
For anonymous users, the default initialization file, if any, is
.kermrc in the chroot'd file system. This default may be overridden
with the --initfile:xxx command-line option. The system
administrator may include commands in this file to disable selected services
for anonymous users, e.g.:
disable delete ; Don't let anonymous users delete files
disable send ; Don't let anonymous users send files
Of course, any Kermit commands at all may be included: settings, macro
definitions, etc. (Also see Section 5.5.)
When the sysadmin specifies the initialization file, this allows a high degree
of fine-grained control over who is allowed access to what commands and
resources, using standard C-Kermit commands, functions, and variables. The
following are particularly useful:
- \v(date), \v(ndate)
- The current date, in case you want to restrict access by date.
(Also read about the new date-related functions in
Section 1.6
of the C-Kermit 7.0
Supplement.)
- \v(day), \v(nday)
- The day of the week, in case you want to restrict access to certain days
of the week.
- \v(home)
- The user's home directory.
- \v(host)
- The hostname of the IKS.
- \v(ipaddress)
- The IP address of the IKS. This and/or \v(host) may be used when you are
running an IKS on multiple hosts and want to have different setups on each,
but still have a common initialization file.
- \v(line)
- The IP host name or address of the client's host.
- \v(time), \v(ntime)
- The current time of day, in case you wish to restrict access to certain
times of day.
- \v(userid)
- The ID with which the user logged in to the IKS. For anonymous logins,
this is "ftp".
So, for example, if the sysadmin wishes to prevent user "olga" from using the
IKS on Mondays, the initialization file could contain a command like:
if equal \v(user) olga -
if equal \v(nday) 1 -
exit 1 Sorry Olga - please come back another day
Or suppose it is desirable to block access from all xyzcorp.com hosts between
9:00am and noon:
if match \v(line) *.xyzcorp.com -
if lgt \v(time) 09:00:00 -
if llt \v(time) 12:00:00 -
exit 1 Sorry - Please come back after noon
Or suppose a certain user is to be allowed to GET files from the server, but
not SEND, PRINT, or MAIL them:
xif equal \v(user) ivan {
disable send
disable print
disable mail
disable enable
}
4.6.1. Introduction
The Internet Kermit Service when built with support for Kerberos 4, Kerberos
5, Secure Remote Password, or OpenSSL's SSL/TLS can be configured to accept,
request, or require secure (authenticated, encrypted, integrity protected)
connections utilizing Telnet Security options.
Kermit 95 2.1 is shipped with support for all of the security options. The
availability of various options is determined by the options selected at
install time.
Instructions for building C-Kermit 8.0 with arbitrary combinations of security
options are available in the C-Kermit Security documentation.
http://www.columbia.edu/kermit/security.html
Most installations of IKSD utilize the TELNET START_TLS option to provide
encrypted and integrity protected connections in conjunction with X.509
certificate based server-side authentication. START_TLS is often combined
with Kerberos, Secure Remote Password, or X.509 client certificates to provide
secure client side authentication. Username and Password prompts are issued
over the TLS connection when secure authentication of the client is
unavailable.
- Retrieve or generate Server Side Certificate and Private Key
- In your IKSD configuration file, \v(common)IKSD.KSC (on Windows)
or /etc/iksd.conf (on Unix), specify these options:
- To request or require the use of TLS, add:
SET TELOPT START-TLS {REQUESTED, REQUIRED}
4.6.3. Configuring IKSD TELNET START-TLS utilizing X.509 Certificates
- Kermit supports the installation of both RSA and DSS certificates.
If you have an RSA-based server certificate then you must specify the
file containing the certificate as well as the file containing the
private key. The private key file must not be encrypted; otherwise,
it will not be able to be loaded by IKSD.
SET AUTH TLS RSA-CERT-FIL C:/OPENSSL/TELNETD-RSA.PEM
SET AUTH TLS RSA-KEY-FIL C:/OPENSSL/TELNETD-RSA-KEY.PEM
- If your certificate is not directly signed by the Root CA, you will
need to include the intermediary CA certificates in a Certificate
Chain file:
SET AUTH TLS RSA-CERT-CHAIN-FILE C:/OPENSSL/TELNETD-RSA-CHAIN.PEM
- If you have an DSS-based server certificate then you must specify the
file containing the certificate as well as the file containing the
private key. The private key file must not be encrypted; otherwise,
it will not be able to be loaded by IKSD.
SET AUTH TLS DSA-CERT-FIL C:/OPENSSL/TELNETD-DSA.PEM
SET AUTH TLS DSA-KEY-FIL C:/OPENSSL/TELNETD-DSA-KEY.PEM
- If your certificate is not directly signed by the Root CA, you will
need to include the intermediary CA certificates in a Certificate
Chain file:
SET AUTH TLS DSA-CERT-CHAIN-FILE C:/OPENSSL/TELNETD-DSA-CHAIN.PEM
- If you wish to restrict the ciphers used to secure the connection you
may do so with the SET AUTH TLS CIPHERS command. If you do not have any
certificates at all to use, specify the use of Anonymous-Diffie-Hellman
ciphers:
SET AUTH TLS CIPHERS ADH
4.6.4. Configuring IKSD to accept Client Side Certificates
- If you wish to accept client certificates you must specify:
SET AUTH TLS VERIFY PEER-CERT
- If you wish to require the use of client certificates specify:
SET AUTH TLS VERIFY FAIL-IF-NO-PEER-CERT
In addition, you must configure where the validation information for the
client side certificates is located. First, the location of the CA
certificates for the validation chain must be specified. This is done
with:
SET AUTH TLS VERIFY-FILE C:/OPENSSL/CA_CERTS.PEM
SET AUTH TLS VERIFY-DIR C:/OPENSSL/CERTS
The location of Certificate Revocation Files must also be specified:
SET AUTH TLS CRL-FILE C:/OPENSSL/CRLS.PEM
SET AUTH TLS CRL-DIR C:/OPENSSL/CRLS
Read about these commands in
http://www.columbia.edu/kermit/security.html
for information on the details of how Certificates and CRLs are stored
in files and directories for use with OpenSSL.
Also, read the section on how to build C-Kermit for different methods of
extracting the userid from the client certificate.
4.6.5. Configuring IKSD TELNET START-TLS Utilizing Kerberos 5 Tickets
When utilizing Kerberos 5 to authenticate the IKSD to the client you
must specify the location of the Kerberos Keytab File:
SET AUTH KRB5 KEYTAB C:/ROOT/KEYTAB
and specify the use of KRB5 ciphers:
SET AUTH TLS CIPHERS KRB5
NOTE: OpenSSL must have been built with support for MIT Kerberos 5.
Configuring IKSD to utilize TELNET AUTHENTICATION options:
- The TELNET AUTH options (KRB4, KRB5, SRP, NTLM) may be used either with or
without the START-TLS option. If you wish to request or require the use of
the AUTH option:
SET TELOPT AUTH {REQUEST, REQUIRED}
- To specify an authentication type(s) use:
SET TELNET AUTH TYPE type(s)
where type(s) is one or more of KRB4, KRB5, SRP, NTLM.
The IKSD behaves at runtime just like the regular C-Kermit program, with
any restrictions resulting from compile-time options, and with the differences
noted in this section and in
Section 4.
When C-Kermit is started as an Internet Kermit Service, the following settings
occur automatically:
- Login (authentication) is required.
- Shell access is disabled.
- Server-side Telnet negotiation is enabled.
- SET RELIABLE ON (see the
C-Kermit 7.0
Supplement).
- FAST file-transfer settings, including "cautious" unprefixing.
- No flow control, no parity.
Items d-f can be overridden with command-line options and/or in the
initialization file.
The IKSD command prompt will not appear, and no commands may be given, before
the user is authenticated.
When the IKSD has been started without the '-x' command-line option, it issues
a Username: prompt. The user may type a username at the prompt, in which case
a Password: prompt is issued, and the user must enter a password. Three login
attempts are allowed, with a pause enforced between each one. If all three
fail, the connection is closed.
The user may also authenticate from the client by sending a [ REMOTE
] LOGIN command (again, only 3 tries are allowed), or by Telnet
Authentication negotiations. Prior to authentication, the IKSD responds to
only the following client commands:
[ REMOTE ] LOGIN
[ REMOTE ] LOGOUT
REMOTE HELP (or RHELP)
REMOTE EXIT (or REXIT)
BYE
Once authenticated, the user may not re-authenticate or change identities.
The connection persists until it is broken in any of the following ways:
- Client sends BYE or REMOTE EXIT (REXIT) or [ REMOTE ] LOGOUT to IKSD.
- Client sends FINISH to IKSD that has been started with "-x".
- User gives HANGUP or CLOSE command to the client.
- User gives EXIT, QUIT, or LOGOUT command at IKSD prompt.
The connection is also closed if the user exits from the client, but only if
it was an end-to-end Telnet connection. There can be no guarantee that
exiting from a serial communication program will close and hang up the serial
connection.
In the IKSD, the DISABLE command applies not only to client/server functions,
but also to the corresponding commands when given at the prompt. For example,
DISABLE DELETE disables not only REMOTE DELETE commands given from the client,
but also DELETE commands given at the IKSD's command prompt, as well as
implicit forms of file deletion, such as when the target of a COPY command is
an existing file.
The DISABLE ENABLE command is irreversible; once this command is given, the
ENABLE command can not be re-enabled, and therefore no other disabled commands
can be enabled either. ENABLE is DISABLEd automatically for anonymous users,
so any DISABLE commands in the anonymous-user initialization file
(Section 4.4) are also irreversible.
All forms of system and shell access are disabled in the IKS. Thus the user
can not execute REMOTE HOST commands from the client, nor access the shell
from the IKS command prompt via shell escapes (!), the RUN or PUSH command, or
by specifying pipes or filters in file-transfer commands, or by pipe
specifications in REMOTE commands, or in any other way. This is true even if
the executable was built without the NOPUSH compile-time option.
Anonymous users are allowed by default, but can be denied with
--anonymous:no on the command line (
Section 4.1).
Anonymous users are handled in about the same way as they are by ftpd. Their
effective user ID is set to "ftp" and their file-system access is restricted
to the tree rooted at the home directory of the "ftp" user, normally
/pub/ftp, via chroot. If /pub/ftp does not exist, login
fails. In that case (or for any other desired reason), the anonymous root
directory can be changed with the --root: option, e.g.
--root:/tmp. Note that, unlike ftpd, iksd does not necessarily
require any particular binaries (such as ls) to be in the chroot'd tree. DLLs
might be another story, but so far these have not been needed, even with
dynamically linked Kermit binaries (at least in Linux and Solaris). Should
DLLs be a problem, use a statically linked Kermit binary (if possible), or
install the needed DLLs in the anonymous root.
File access is according to user "ftp" and the directory and file
permissions of the /pub/ftp tree. If anonymous uploads are to be
allowed, then usually only specific directories (often with a name like
"incoming") are given write permission, and any files that are created in
such a directory have owner "ftp", with the group set to the group of the
directory. As noted in Section 4.1, the permission for
all files created by anonymous users is 0040 (group-read only), or whatever
else the sysadmin has specified in the --permissions: command-line
option.
Thus, if you already have a public ftp server, most likely everything is set
up appropriately already. If anonymous ftp is
allowed (by the presence of a valid user "ftp" in your system's password
file), it will be allowed also for IKSD unless explicitly disallowed on the
IKSD command-line (or if /pub/ftp doesn't exist and you did not
supply a --root: option on the command line).
In addition to the FTP-like restrictions, certain Kermit services are always
denied to anonymous users. These include:
- PRINT (at IKSD prompt) and REMOTE PRINT (from client)
- MAIL (or SEND /MAIL) at IKSD prompt and from client.
- Creation of any logs (transaction, debug, packet, etc).
- No file may be deleted, including implicitly, e.g. by the COPY command.
- FILE COLLISION is set to RENAME and may not be changed.
The latter three provisions mean that anonymous users can not delete,
overwrite, rename, or alter any existing files in any way, whether by file
transfer or with the DELETE or RENAME command.
Note that IKSD, like FTPD, does not allow directory creation by anonymous
users, even when file/directory permissions would otherwise allow it. To
change this, add:
enable mkdir ; Enable directory creation
to /pub/ftp/.kermrc (or whatever other initialization file you have
designated for anonymous users with --initfile). Similarly for
directory removal:
enable rmdir ; Enable directory removal
Of course directories can be removed only if (a) they are empty, and
(b) their permissions allow it.
The command-line argument vector, normally accessible in the
\&@[] array, the top-level \%0..9 variables, or by other means,
is inaccessible to IKSD users. Thus IKSD clients can not discover the IKSD
startup path or options, the logfile pathnames or directories, logging level,
etc.
Several services that are normally provided by C-Kermit are not available
when it is an Internet Kermit Service Daemon.
If the user has access to the IKSD command prompt, why not allow her to "set
host" or "set line" from there to another place? Obviously this would be a
security risk if allowed for anonymous users. For authenticated users, it
should be OK, but is not currently possible for Telnet connections since the
IKSD is already a Telnet server on the incoming connection, and is not
designed to conduct two separate Telnet sessions simultaneously. It might be
possible to allow the user to make a dialout connection, but some coding and
testing would be needed should this prove desirable.
Shell access is forbidden to anonymous users for obvious reasons. From a
security standpoint, it could be allowed for authenticated users, but there
remains a technical obstacle: the absence of a terminal driver for the
connection.
External protocols such as Zmodem can not be expected to perform any of the
logging or security functions that are done by C-Kermit itself within its
protocol and file modules. Thus external protocols are disabled in the IKSD.
Plus the fact that such protocols are likely to be incompatible with Telnet
connections in the first place. In more detail:
- When the user is 'anonymous' the file system is chroot'd, which means
that any external executables must exist in the chroot'd file system.
This leaves open the possibility that executables might be replaced by a
different file of the same name that has been uploaded either on top of
the existing file or just into the same directory. If "." is in the
PATH for the process anything the user uploads with the name 'rz' or
'sz' might be executed in its place. Therefore, the IKSD does not use
any external commands of any kind. Not 'ls', not 'cp', not 'df', not
anything. To allow the execution of external programs is a major
security hole in this setting.
- Most implementations of 'sz' and 'rz' are designed for remote use over a
terminal connection. They expect to be run underneath a pseudoterminal
(PTY). When IKSD is running there is no PTY. In fact, when IKSD is
running there is only a raw socket; the IKSD handles all necessary
Telnet protocol translations including Telnet Network Virtual Terminal
(NVT) rules regarding quoting of Carriage Return and 0xFF depending upon
the state of the BINARY Telnet option in each direction. 'sz' and 'rz'
are completely incapable of performing these translations in either
direction and any attempt to transfer a file with them will result in a
transfer failure and the corruption of the data stream.
- IKSD supports encrypted sessions, in which case it handles the
encryption and decryption itself; an external protocol module would not
do this, and so could not be used on encrypted channels in any case.
Certain options available in wu-ftpd are not implemented in iksd:
- Ability to select IKSD logging for real vs anonymous users.
- Ability to select IKSD logging for inbound vs outbound files.
- Currently all transfers are logged or not logged.
- Ability to allow/restrict chmod/delete/overwrite for anonymous users.
- Currently there is no command for changing file permissions.
- Guests may not delete files, period.
- FILE COLLISION is set to RENAME for guests and may not be changed
since all the other options allow existing files to be altered.
- There is no way to grant these capabilities to guests.
- Ability to allow directory creation by anonymous users.
- Anonymous users may not create or remove directories.
- Ability to allow/specify CD messages on a per-directory basis.
- RFC931 authentication of remote (client) user (but wu-ftpd doesn't either).
These or other controls can be added if there is sufficient reason or demand.
- When commands are logged in syslog, the EXIT command appears twice.
- wtmp entries show pids in hex due to length restrictions, so you'll
need to convert them to decimal before using them with ps, kill, etc.
Unless you disable it, all IKSDs keep current session information in a shared
database. The IKSD instances can be within one computer or running on any
number of different computers that share the same file system on the same
network. The database can be monitored by the sysadmin with a simple
"systat"-like display program, which shows who is logged in, from where, and
what they're doing. (The idea is easily adapted to other servers, such as
FTP.) For maximum portability and reliability, the database is an ordinary
file on disk.
The IKSD database file should reside in its own directory (to avoid conflicts
with other servers that might use the same filename conventions), and this
directory and its files should be visible to the sysadmin without privileges
(e.g. by group access) but hidden from the public for privacy reasons if other
such logs (e.g. the ftpd log, syslog, etc) also are.
The database is a random-access file indexed by "slot number", which is
self-assigned during a quick search at startup. Once a slot is claimed, there
is no more searching; each IKSD updates its own slot in place and does not
touch the others. Slots never move.
When an IKSD instance starts, it must obtain a "slot allocation lock" before
it can claim its slot. Otherwise there could be a race condition when another
IKSD instance starts at the same time, in which the two could wind up with the
same slot.
Since exclusive access is a nonportable concept, we obtain the lock in a
crude but portable manner, without recourse to kernel locks, interprocess
communication, semaphores, memory-mapped files, or other platform-specific
mechanisms:
- Create a temp file in the database directory called
ip.pid,,
where ip is the local IP address as 8 hex digits and pid is my
own process ID (PID) in hex (no leading zeros). This is guaranteed to be a
unique name (and if by chance a file of this name already exists, it can't
possibly be valid, so it it's ok to overwrite it).
- Write my own ID string into the file. The ID string is
ip:pid, where ip is (again) my IP address as 8 hex
digits, and pid is my PID in decimal (not hex). (The reason for
decimal here is readability, so sysadmins can easily enter it into other tools
or commands; it has to be hex in the temp filename for compactness in case of
14-character filename limitations.)
- Try to open iksd.lck, which is the real lockfile. If this
succeeds, read its contents (an ip:pid string). If the
ip not the same as
mine, consider the file locked. If it is the same, extract the PID
and check its validity. If it is not valid, delete the lockfile.
(Currently this step is skipped by K95 since it can't check PIDs.)
- At this point the iksd.lck file might or might not exist. Try to
rename the temp file to iksd.lck. This will fail if the lockfile
exists, in which case we sleep, loop, and try again, up to a certain
number of times -- say 16 tries spaced 1 second apart. If we fail to
get a lock, we let the user on anyway, in the spirit of service over
management. If the rename succeeds, on the other hand, we have a lock.
When and if we have obtained a lock, we open the database file itself and
search the whole database (sequentially) for:
- Free slots (In-Use flag is 0), or:
- Stale slots(*), or:
- Any slot with our own IP and PID (a special kind of stale slot).
(*) In-Use flag is 1 and IP address is ours, but PID is invalid.
In C-Kermit only (not K-95) we also perform some housekeeping duties while
searching (the Windows APIs include no provisions for this):
- Whenever a stale slot is found, we free it (set its In-Use flag to 0).
- We remove all free slots after the last in-use slot by truncating the
database file (this keeps the database file from constantly growing as
new highwater marks are reached).
Then we claim the first one of these that was found. If no slot was claimed,
we add a new slot at the end and claim it. If the database file did not
exist, we create it and claim the first slot. (In Windows, the IKSD listener
simply deletes the existing database, if any, on initial startup.)
To claim a slot:
- We set the In-Use flag to 1, fill in the Server PID and IP address
fields with our own PID and IP address, fill in the session-start and
update time fields, and clear the other fields.
- Then we release the lock.
From this point, we can write freely into our slot regardless of locks.
Notes:
- Since all IKSDs follow the same procedure, only one can have a lock a
at a time.
- The lockfile is readable text; it can be typed (cat'd). The contents
are the same format on every platform, regardless of byte order or
word size.
- This scheme allows (but does not require) multiple computers that share
a common file system to have a single IKSD database, which in turn allows
the site manager to monitor all IKSDs on all computers at once. This
works if each computer has a unique IP address (which it must if they are
on the same network sharing a common file system; nevertheless, care must
be taken regarding IP address pools, etc). It also depends on the file-
sharing mechanism (such as NFS) to propagate updates promptly and in
sequence.
- While one IKSD is allocating its slot, nothing prevents other IKSD
instances that already have their own slots from updating them, since
that does not interfere with slot allocation.
- The tempfile name format is UNIXish and will need modification for file
systems with restrictive names, such as FAT, 14-char UNIXes, etc. In
such cases we could (a) omit the IP address if we're not concerned about
multiple computers sharing a single database, or (b) encode the IP
address in Base 64 to make it shorter. But probably none of this will
ever come up.
- The design accommodates 64-bit IPv6 addresses, but for now the software
uses only 32 bits.
A slot is 4K (4096 octets), divided into 4 1K chunks. The first chunk is
further subdivided into shorter fields. Numeric fields are coded in
hexadecimal, right-adjusted, and left-padded with 0's. Text fields are
left-adjusted and right-padded with blanks. Date-time fields are
right-adjusted within a field of 18 with the leading blank reserved for Y10K.
Date-time format is:
yyyymmdd hh:mm:ss
where yyyymmdd are the numeric year, month, and day, and hh:mm:ss are
the hour (24-hour clock), minute, and second. Months and days are 1-based,
leading 0's are supplied where needed.
The layout of each slot is as follows (fields and byte positions are numbered
from 0):
0. FLAGS (Slot/Session Flags)
Start: 0
Length: 4
Type: Bit Mask
Format: Hex digits.
Bit Values:
1: 1 = Slot in use, 0 = Slot is free.
2: 1 = Real user, 0 = Anonymous user.
4: 1 = Logged in, 0 = Not logged in.
1. AUTHTYPE (Authorization Type)
Start: 4
Length: 4
Type: Number
Format: Hex digits.
Values:
0: None 8: (reserved)
1: Kerberos IV 9: (reserved)
2: Kerberos V 10: LOKI
3: SPX 11: SSA
4: MINK 12: KEA_SJ
5: SRP 13: KEA_INTEG
6: RSA 14: DSS
7: SSL 15: NTLM
2. AUTHMODE (Authorization Type)
Start: 8
Length: 4
Type: Number
Format: Hex digits.
Values:
0: Rejected
1: Unknown
2: Other
3: User
4: Valid
3. STATE (IKSD State)
Start: 12
Length: 4
Type: Bit Mask
Format: Hex digits.
Bit Values:
1: Initializing
2: Sending a file
4: Receiving a file
8: Executing a REMOTE command
32: At command prompt
4. PID (IKSD's Process ID)
Start: 16
Length: 16
Type: Number
Format: Hex digits.
5. SERVER IP (IKSD's IP Address)
Start: 32
Length: 16
Type: IP address as a series of numeric octets in network byte order
Format: Hex digits
6. CLIENT IP (Client's IP Address)
Start: 48
Length: 16
Type: IP address as a series of numeric octets in network byte order
Format: Hex digits
7. SESSION START (Date and Time session started)
Start: 64
Length: 18
Type: Date-time
Format: Date-time string
8. LAST UPDATE (Date and Time this record was last updated)
Start: 82
Length: 18
Type: Date-time
Format: Date-time string
9. ULENGTH (Username length)
Start: 100
Length: 4
Type: Number
Format: Hex digits, right adjusted
10. DLENGTH (Length of current directory)
Start: 104
Length: 4
Type: Number
Format: Hex digits, right adjusted
11. ILENGTH (Length of state-specific information)
Start: 108
Length: 4
Type: Number
Format: Hex digits, right adjusted
12. RESERVED
Start: 112
Length: 912
Type: None
Format: Filled with blanks
13. USERNAME (Username; if anonymous "anonymous:password")
Start: 1024
Length: 1024
Type: None
Format: Text, ULENGTH significant chars, right-filled with blanks
14. DIRECTORY (Current directory)
Start: 2048
Length: 1024
Type: None
Format: Text, DLENGTH significant chars, right-filled with blanks
15. INFO (State-specific information)
Start: 3072
Length: 1024
Type: None
Format: Text, ILENGTH significant chars, right-filled with blanks
The state-specific information tells you whether IKSD is at its command prompt
or in server command wait, if it is sending or receiving a file (in which case
the filename is shown), it is executing a REMOTE command (in which case the
command is shown), or how it was terminated (BYE, REMOTE EXIT, disconnect, etc)
Notes:
- There are no control characters (CR, LF, NUL, etc) or 8-bit
characters; only ASCII graphic characters are used in the
database. Fields are left- or right-padded with Space or '0' as
indicated.
- Since the USERNAME, DIRECTORY, and INFO fields are right-padded
with spaces, it would be laborious to isolate their actual values
by trimming spaces from the right (since we must allow for
internal spaces); hence the ULENGTH, DLENGTH, and ILENGTH fields.
- The USERNAME, DIRECTORY, and INFO fields are 1K each since 1K is
the maximum pathname length found on common UNIX platforms (even
though many platforms have smaller maximums). Thus, for example,
the current directory string might be exactly 1K long. This is why
its length is kept outside the block. Also the division of the
record into four 1K blocks tends to make for more efficient i/o.
- The IKSD database does not provide a permanent record or give
complete information. That's what the syslog entries and the IKSD
log are for.
The straightforward data definitions and formats allow a display module to be
written easily in the language of your choice, including scripting languages
such as Kermit's own. A sample display module, iksdpy, is provided as a
"Kerbang" script, providing a running display of the active IKSD sessions from
the database. In its startup mode, it lists each session in the database,
refreshing every 4 seconds. Various keystroke commands are available for
help, quitting, etc, and to enter the detail screen for a specific session.
The detail screen, too, refreshes itself every 4 seconds. Here you have keys
to return to the main screen, to pick another session, to cycle through
sessions, and so on.
When a slot is freed, its information is left intact so you can still see who
was using it, when, and from where, and the last thing they did before logging
out. The old info persists until the slot is removed or reclaimed, which will
happen when the next new IKSD session starts.
The iksdpy script is short, simple, and easily extensible. For example, while
watching a detail screen and you see somebody doing something bad, you might
like to have a "K" key to kill the session (the script already knows the pid,
so it need simply form a "!kill -9" command, including the pid).
The following command-line options let you disable/enable the database and
specify its location:
- --database:{on,off}
- Whether an active-sessions database should be kept. On by default.
If "on", but --dbfile is not specified, /var/log/iksd.db is
used.
- --dbfile:filename
- Use this option to specify an iksd database file name. If you include
this option, it implies --database:on.
In UNIX, the system startup procedure can delete the database file before
starting inetd, since nothing in it is valid; however, this is not necessary
since normal cleanup procedures will do the job too. In Windows, the IKSD
listener takes care of it.
To capture a snapshot of IKSD usage, simply copy the database file.
In case you want to test IKSD on a port other than 1649, be aware that
IKS-aware Kermit clients (such as C-Kermit 7.0 and K95 1.1.18 and later) will
not initiate Telnet negotiations with it, since it is not on a Telnet port
(i.e. 23 or 1649). To get correct operation you'll need to force the client
to negotiate, e.g.:
telnet hostname 3000
set host hostname 3000 /telnet
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C-Kermit IKSD Administration /
Columbia University /
[email protected] /
12 Dec 2001