ttysnoop(8) snoop on a user's tty


ttysnoop [pty ]


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


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.




The program is unable to do any terminal control-code translations for the original tty and the snoop-device. I doubt it will ever do this.


Carl Declerck, [email protected]