in continuation to the previous post, i made a test that seemed to work
(at least partially) to regain control of 'ncftp':
1. in a shell attached to /dev/tty1, i ran 'nohup ncftp'.
i didn't connect to any server, and then ctrl-Z, 'bg', and 'exit' (had
to 'exit' twice, since the shell notices there's a suspended process).
note: the shell i use is 'tcsh'.
2. opened a shell on '/dev/tty4'.
3. on a shell attached to '/dev/tty5' i run a debugger:
gdb /usr/bin/ncftp 7787
in the debugger:
(gdb) print open("/dev/tty4", 0) /* '0' stands for O_RDONLY */
$ = 4
(gdb) print dup2(4, 0);
$ = 0
(gdb) print open("/dev/tty4", 01) /* '01' stands for O_WRONLY */
$ = 5
(gdb) print dup2(5, 1);
$ = 0
(gdb) print dup2(5, 2);
$ = 0
(gdb) set variable stdin = fdopen(0, "r")
(gdb) set variable stdout = fdopen(1, "a")
(gdb) set variable stderr = fdopen(2, "a")
(gdb) quit
The program is running. Quit anyway (and detach it)? (y or n) y
Detaching from program: /usr/bin/ncftp, Pid 7787
> kill -CONT 7787
4. i switched back to the shell of "/dev/tty4", and typed 'ls' and ENTER.
then i got a response from ncftp (regarding not being connected to any
server), and then i got its prompt. i then could continue working with
it. note that it took over the terminal - i had no way to talk to the
shell. presisng ctrl-Z just gave a beep. pressing ctrl-C caused ncftp
to exit, and then i got the shell's prompt.
btw, with 'ftp' - i could make the process remain alive when i closes its
original shell. apparently, it agrees to remain active only if it's in the
middle of a file transfer operation.
so, this method seems to work in some way. note that i didn't try leaving
ncftp backgrounded for a long duration, and i also didn't try to actually
connect to a server with it (i tried to some invalid address and it gave
me the normal DNS lookup error, and then i decided to check what ctrl-Z
and ctrl-C do.... ;) ).
i think this calles for a 'bdetach' and a 'battach' set of shell/perl
scripts. 'battach' will do what i listed above. 'bedtach' will set a
termporary tty for the process (attach a debugger to it, open a new pty,
and set it as stdin for the process, and set /dev/null as stdout and
stderr for the process) and make it imune to HUP signals.
it'll be interesting to check this method on the shell itself. if it'll
work, it'll give a screen-like behaviour without having to run screen in
advance, or having it installed on the system. any system with a debugger
on it will work...
--
guy
"For world domination - press 1,
or dial 0, and please hold, for the creator." -- nob o. dy
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