The
ttysnoop
/
ttysnoops
client-server combo can be used to snoop (watch) on a user's login tty.
The server
(ttysnoops
)
is usually started by getty(8) or telnetd(8) and reads the file
/etc/snooptab
to find out which tty's should be cloned and which programs to run on them
(usually /bin/login). A tty may be snooped through a pre-determined (ie.
fixed) device, or through a dynamically allocated pseudo-tty (pty). This is
also specified in the
/etc/snooptab
file. To connect to the pty, the client
ttysnoop
should be used. The available pseudo terminals pty are present as
sockets in the directory /var/spool/ttysnoop/.
Format of /etc/snooptab
The
/etc/snooptab
file may contain comment lines (starting with a '#'), empty lines, or entries
for tty's that should be snooped upon. The format of such an entry is as
follows:
tty snoop-device type program
where
tty
is the leaf-name of the tty that should be snooped upon (eg. ttyS2, not
/dev/ttyS2) OR the wildcard '*', which matches ANY tty.
snoop-device
is the device through which
tty
should be snooped (eg. /dev/tty8) OR the literal constant "socket". The
latter is used to tell
ttysnoops
that the snoop-device will be a dynamically allocated pty.
type
specifies the type of program that should be run, currently recognized
types are "init", "user" and "login" although the former two aren't really
needed. Finally,
program
is the full pathname to the program to run when
ttysnoops
has cloned
tty
onto
snoop-device
EXAMPLE
The following example
/etc/snooptab
file should illustrate the typical use of
ttysnoop
/
ttysnoops
#
# example /etc/snooptab
#
ttyS0 /dev/tty7 login /bin/login
ttyS1 /dev/tty8 login /bin/login
#
# the wildcard tty should always be the last one in the file
#
* socket login /bin/login
#
# example end
#
With the above example, whenever a user logs in on /dev/ttyS0 or /dev/ttyS1,
either tty will be snooped through /dev/tty7 or /dev/tty8 respectively. Any
other tty's will be snooped through a pty that will be allocated at the time
of login. The system-administrator can then run
ttysnoop pty
to snoop through the pty. Note that it is up to the system-administrator to
setup getty and/or telnetd so that they execute
ttysnoops
instead of /bin/login.