tac_plus
tac_plus(8) System Manager's Manual tac_plus(8)
NAME
tac_plus - tacacs plus daemon
SYNOPSIS
tac_plus -C <configfile> [-GghiLPSstv] [-B <bind_address>] [-d <level>] [-l <logfile>] [-p <tcp_port>] [-u
<wtmpfile>] [-w <wholog>]
DESCRIPTION
By default, tac_plus listens on tcp port 49 and provides network devices (normally routers and access
servers) with authentication, authorization and accounting services.
A configuration file controls the details of authentication, authorization and accounting.
COMMAND-LINE OPTIONS
-C <configfile>
Specify the configuration file name. The -C option is required.
-B <bind address>
Specify the address on which the daemon should bind(2). Successive instances of -B override
previous instances. By default, the daemon listens on all addresses. Note: this changes the name
of the pid file created by the daemon.
-G Remain in the foreground, but not single-threaded nor logging to the tty.
-d <level>
Switch on debugging. By default the output will appear in the log file and syslog(3).
NOTE: The -g flag will cause these messages to also appear on stdout. The -t flag will cause these
messages to also be written to /dev/console.
The value of level is as described below. These values represent bits that can be logically OR'd
together. The daemon logically ORs successive occurrences of the -d option.
Value Meaning
2 configuration parsing debugging
4 fork(1) debugging
8 authorization debugging
16 authentication debugging
32 password file processing debugging
64 accounting debugging
128 config file parsing & lookup
256 packet transmission/reception
512 encryption/decryption
1024 MD5 hash algorithm debugging
2048 very low level encryption/decryption
32768 max session debugging
65536 lock debugging
-g Single threaded mode. The daemon will only accept and service a single connection at a time
without forking and without closing file descriptors. All log messages appear on standard output.
This is intended only for debugging and not for normal service.
This option does not work with single-connection sessions.
-h Display help message.
-i tac_plus will be run from inetd(8). In inetd mode, the configuration file is parsed every time
tac_plus starts.
If the configuration is large or the frequency of connections is high, this negatively will affect
the responsiveness of the daemon.
If the config file is small, connections are infrequent, and authentication is being done via
passwd(5) files or SKEY (which are not cached), running in inetd mode should be tolerable, but
still is not recommended.
This option does not work with single-connection sessions.
-l <logfile>
Specify an alternate log file location. This file is only used when the -d option is used. The
logs are still posted to syslog.
-L Lookup DNS PTR (Domain Name System PoinTeR) record of client addresses. The resulting FQDN (Fully
Qualified Domain Name), if it resolves, will be used in log messages, libwrap (tcp_wrappers)
checks, and for matching host clauses of the configuration file. Also see tac_plus.conf(5).
-P Parse the configuration file, echo it to standard output while parsing, and then exit. tac_plus
will exit non-zero when a parser error occurs.
Useful for debugging configuration file syntax.
-p <port>
Listen on the specified port number instead of the default port 49 for incoming tcp connections.
Note: this changes the name of the pid file created by the daemon.
-S Enables or allows client single-connection mode, where-by the client will create one connection and
interleave queries.
Note: this is broken in IOS and IOS-XE.
Note: this is currently only partially supported in the daemon.
-s Causes the daemon to always reject authentication requests which contain a minor version number of
zero (SENDPASS). This enhances security in the event that someone discovers your encryption key.
SENDPASS requests permit requesters to obtain CHAP, PAP and ARAP passwords from the daemon, iff the
encryption key is known.
Note: IOS versions preceding 11.2 will fail.
-t Log all informational, debugging or error messages to /dev/console in addition to logging to
syslogd. Useful for debugging.
-u <wtmpfile>
Write wtmp entries to the specified wtmp file.
-v Display version information and exit.
-w <wholog>
Specify the location of the max session file.
STARTING
tac_plus is normally invoked by root, as follows:
# tac_plus -C <configfile>
where <configfile> is a full path to the configuration file. Tac_plus will background itself and start
listening on port 49 for incoming tcp connections.
Tac_plus must be invoked as root to obtain privileged network socket 49 and to read the protected
configuration file, which may contain confidential information such as encryption keys and cleartext
passwords.
After the port is acquired and the config file is read, root privileges are no longer required. You can
arrange that tac_plus will change its user and group IDs to a more innocuous user and group via the
configuration file.
NOTE: The new user and group still needs permission to read any passwd(5) (and shadow(5)) files and S/KEY
database if these are being used.
TCP WRAPPERS
If tac_plus was compiled with libwrap (aka. tcp_wrappers) support, upon connection the daemon will consult
with tcp_wrappers on whether the client has permission to connect. The daemon name used in a daemon list
of the access control file is the name of the executable, normally "tac_plus". See hosts_access(5).
PERMISSIONS
The configuration file should be unreadable and unwriteable by anyone except root, as it contains
passwords and keys.
SIGNALS
If the daemon is receives a SIGHUP or SIGUSR1, it will reinitialize itself and re-read its configuration
file.
Note: if an error is encountered in the configuration file or the file can not be opened for reading, such
as due to insufficient permissions resulting from process ownership and file permissions, the daemon will
exit.
Likewise, if the daemon is configured to send accounting records to a file and that file can not be opened
for writing, such as due to insufficient permissions resulting from process ownership and file
permissions, the daemon will exit.
LOG MESSAGES
tac_plus logs error and informational messages to syslog facility LOG_DAEMON.
FILES
/var/log/tac_plus.acct Default accounting file.
/var/log/tac_plus.log Default log file used when the -d option is used.
/var/run/tac_plus.pid Pid file. If the -B option is used, ".bind_address" is appended. If the -p
option is used, ".port_number" is appended.
SEE ALSO
tac_plus.conf(5), tac_pwd(8)
Also see the tac_plus User Guide (user_guide) that came with the distribution. The user guide does not
cover all the modifications to the original Cisco version.
HISTORY
There are at least 3 versions of the authentication protocol that people commonly refer to as "TACACS".
The first is ordinary tacacs, which was the first one offered on Cisco boxes and has been in use for many
years. The second is an extension to the first, commonly called Extended Tacacs or XTACACS, introduced in
1990.
The third one is TACACS+ (or T+ or tac_plus) which is what is documented here. TACACS+ is NOT COMPATIBLE
with any previous versions of tacacs.
AUTHOR
The tac_plus (tacacs+) developer's kit is a product of Cisco Systems, written by Lol Grant. Made
available at no cost and with no warranty of any kind. See the file COPYING and source files that came
with the distribution for specifics.
Though heavily modified from the original Cisco manual pages, much of the modifications are derived from
the tacacs IETF draft and the Cisco user guide.
28 July 2009 tac_plus(8)