How to secure my script from Ctrl-C

jhansrod · May 17, 2005, 10:02am

Hi all

I am looking for a way to ensure that once a user is logged in and running a script, he cannot break out of it.

Thanks

J

dangral · May 17, 2005, 10:21am

Look into the command trap

jhansrod · May 17, 2005, 10:31am

I have tried checking this out. I am on AIX 5.2 and there is no man entry for this. Can anyone give me an idea on how to use it ?

Thank you

vgersh99 · May 17, 2005, 10:34am

what shell are you using?

if using ksh, 'man ksh' and search for 'trap'

jhansrod · May 17, 2005, 10:38am

I am using ksh. I have checked it out and all it talks of is

-e Executes the ERR trap, if set, and exits if a command has a nonzero exit
status. This mode is disabled while reading profiles.

What next....

Thanks

vgersh99 · May 17, 2005, 10:42am

Solaris' "trap" is more descriptive then that.
Are you sure you don't see anything more about 'trap' in 'man ksh'?

jhansrod · May 17, 2005, 10:50am

100%. Anyone with an idea of what is to be done in AIX.

Thanks

J

dangral · May 17, 2005, 10:54am

For more go here

trap [Command] [Signal] ... Runs the specified command when the shell receives the specified signal or signals. The Command parameter is read once when the trap is set and once when the trap is taken. The Signal parameter can be given as a number or as the name of the signal. Trap commands are executed in order of signal number. Any attempt to set a trap on a signal that was ignored on entry to the current shell is ineffective.

If the command is -, all traps are reset to their original values. If you omit the command and the first signal is a numeric signal number, then the ksh command resets the value of the Signal parameter or parameters to the original values.

Note: If you omit the command and the first signal is a symbolic name, the signal is interpreted as a command.

If the value of the Signal parameter is the ERR signal, the specified command is carried out whenever a command has a nonzero exit status. If the signal is DEBUG, then the specified command is carried out after each command. If the value of the Signal parameter is the 0 or EXIT signal and the trap command is executed inside the body of a function, the specified command is carried out after the function completes. If the Signal parameter is 0 or EXIT for a trap command set outside any function, the specified command is carried out on exit from the shell. The trap command with no arguments prints a list of commands associated with each signal number.

For a complete list of Signal parameter values used in the trap command without the SIG prefix, see the sigaction, sigvec, or signal subroutine in the AIX 5L Version 5.3 Technical Reference: Base Operating System and Extensions Volume 2.

jhansrod · May 17, 2005, 11:00am

Any ideas on how do I use this ?

dangral · May 17, 2005, 11:04am

The short of it:

trap "" 2

jhansrod · May 17, 2005, 11:08am

Thanks for the reply, however this still allows the user to break out with Ctrl-C.

Any ideas.

dangral · May 17, 2005, 11:22am

Run this script and see what happens when you try to ctrl-c in the first 20 seconds after the script starts. Then try to ctrl-c after you see the echo statement.

#! /bin/ksh

trap "" 2

sleep 20
echo "done with first sleep. You may interrupt now."
trap "exit" 2
sleep 20

jhansrod · May 17, 2005, 11:38am

Thanks. This has done the trick. Could there be a reason why if I had #!/usr/bin/ksh it would not work ?

Regards

J