i/o STOP + CONT (bash?) problem

Chris Faylor cgf@cygnus.com
Tue Sep 5 22:37:00 GMT 2000


On Wed, Sep 06, 2000 at 01:34:44AM -0400, Chris Faylor wrote:
>On Wed, Sep 06, 2000 at 03:51:27PM +1000, Benjamin Low wrote:
>>Thanks for the prompt reply.
>>
>>Chris Faylor wrote:
>>...
>>> Um.  CTRL-S has nothing to do with the STOP signal.  
>>
>>As I understand (understood :-) it, the terminal driver issues various
>>signals to the current process in response to predetermined input
>>sequences (set via stty). Thus with the "standard" stty config, ctrl-C
>>sends an SIGINT, ctrl-S sends SIGSTOP, etc. This gels with my practical
>>experience in that kill -STOP|-CONT <pid> works the same as
>>ctrl-S|ctrl-Q (on every unix I've worked on (linux, solaris,
>>cywgin-sometimes).
>
>Sorry, you are understanding wrong.  CTRL-S (aka XOFF) does not send
>SIGSTOP.
>
>At a gross level, I guess you could say that sending a SIGSTOP to
>a signal stops a process similarly to the way that typing CTRL-S
>stops output but the two are really very different.
>
>You can verify this on linux by doing a 'ps' on a test process.  It will
>be in the 'T' state if you've do a 'kill -STOP' to the process.  It
>will also be in a 'T' state if you type CTRL-Z.
>
>It will be in some other state ('S', probably) when you've stopped the
>output with CTRL-S.
>
>For fun, once you've done this, try doing a 'kill -CONT' on the
>process where you just typed CTRL-Q.  You won't see any change.
			      CTRL-S

cgf

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