On Mon, Sep 28 at 11:24, Stephen Pelc wrote:
> I need to determine if my Linux program is running detached,
> e.g. if it was launched by
> vfxlin
> or
> vfxlin &
Uhm the second process isn't detached it's backgrounded which
isn't the same thing, it will still have a controlling terminal.
If your question was "Is my program in foreground or background?"
the following C demo should help. It works by comparing the
programs process group with that currently selected foreground
group on the controlling terminal. Also demos basic detached
opertion detection along the way.
> Is there a standard way for the vfxlin program to determine
> this? It would also be useful to know if input or output is
> being piped.
fstat() on the file descriptor should help. The st_mode field
should help you distingush between plain files, character
devices (tty or /dev/null etc) and fifo/pipes.
/*
* Work out if a program is in foreground or background.
*
* Report result via syslog for detached process, and
* via stderr for attached.
*/
#include <sys/types.h>
#include <stdio.h>
#include <unistd.h>
#include <syslog.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#define INIT_PID 1
int
main( int argc, char *argv[] )
{
int fd;
pid_t ppid;
pid_t mypgrp;
pid_t ctpgrp;
char *myname;
int i;
/* Get the program name for reports */
myname = strrchr( argv[0],'/');
if ( myname )
myname++;
else
myname = argv[0];
/* Try to open the controlling tty */
fd = open("/dev/tty", O_RDONLY );
if ( fd < 0 )
{
/* No controlling tty, report via syslog */
ppid = getppid();
if ( ppid == INIT_PID )
syslog( LOG_INFO,"%s is detached child of init.", myname );
else
syslog( LOG_INFO,"%s is detached child of PID %d.", myname, ppid );
exit( 0 );
}
/* Get our process group */
mypgrp = getpgrp();
/* Now report our state 10 times to allow playing for fg/bg settings */
for ( i = 0 ; i < 10 ; i++ )
{
/* Get the controlling terminal group */
ctpgrp = tcgetpgrp( fd );
/* Report */
if ( ctpgrp == mypgrp )
fprintf( stderr,"%s is in foreground. (%d)\n", myname, mypgrp );
else
fprintf( stderr,"%s is in background. (%d != %d)\n", myname, mypgrp, ctpgrp );
sleep( 2 );
}
close( fd );
exit( 0 );
}
--
Bob Dunlop
