How to kill zombie processes?

Question

I have two problems: a program I made am glitching out and making nearly unkillable processes, if either subproblem is solved I believe both problems will be easily resolved. I am running an early 2008 Macbook on OSX 10.6.8.

/Problem #1, coding:/

I've been playing around with the iRobot Create using termios.h I/O. I compile without warnings or errors and can run the program without a hitch. I am connecting to the robot by usb which explains the input "/dev/tty.usbserial".

 gcc simple.c -o simple
 ./simple /dev/tty.usbserial

The program starts by checking the arguments given, then tries to connect with the given argument (char * device is /dev/tty.usbserial) with the biscConnect() function. It fails on my mac.

//in file simple.c:
int main(int argc, char *argv[]){
if(argc!=2){
    printf("Put port... like /dev/tty.usbserial or something\n");
    exit(EXIT_FAILURE);
}
printf("Starting...\n");
biscConnect(argv[1]);
}
void biscConnect(char *device){
struct termios tty;

// Try to open the device from the input
    if((fd = open(device, O_RDWR | O_NOCTTY | O_NONBLOCK))==-1){
        fprintf(stderr, "Serial port at %s could not be opened: %s\n", device, strerror(errno));
        exit(EXIT_FAILURE);
    }
     tcflush (fd, TCIOFLUSH);
     tcgetattr(fd, &tty);
     tty.c_iflag     = IGNBRK | IGNPAR;
     tty.c_lflag     = 0;
     tty.c_oflag     = 0;
     tty.c_cflag     = CREAD | CS8 | CLOCAL;
     cfsetispeed(&tty, B57600);
     cfsetospeed(&tty, B57600);
     tcsetattr(fd, TCSANOW, &tty);

     //The code fails prior to this point
}

I would then send bytes to the robot to make it move if it didn't get stuck before then.

/Problem #2, unkillable processes:/ When I run the file, the terminal goes into a weird mode where the prompt is gone and I can type anything I want (usually signifying a process is running). I cannot exit using control-c. The only way I can seem to exit is closing the terminal window. This fails to kill the running process.

I can easily look up the pid but the Activity Monitor but the Force Quit fails to kill the process, kill -9 [pid] fails, killall [program name] fails etc. despite acknowledging the existence of the program. The only way to force terminate the process seems to be to physically close off the power from the computer and reboot it (ie shuting down doesn't work because it tries, and fails, to terminate the process(es)). I am wasting a terrible amount of time if to debug the program I need to power-cycle my laptop every run! I can continually create more process but am unable to delete them.

I think if I knew the parent process I might be able to kill these "zombie" processes but I don't know what the parent is.

Any ideas on how to get rid of these processes without power-cycling would be tremendous help, thanks!

Answer 1

On Mac OS X 10.8.4, I created a program zombie from zombie.c:

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

int main(void)
{
    pid_t pid;

    if ((pid = fork()) >= 0)
    {
        if (pid == 0)
        {
            printf("%d: committing suicide (parent %d)\n", (int)getpid(), (int)getppid());
            exit(0);
        }
        else
        {
            printf("%d: going to sleep for a while - child %d might die while I snooze\n",
                (int)getpid(), (int)pid);
            sleep(30);
            printf("%d: awake\n", (int)getpid());
        }
    }
    return 0;
}

When I ran it in one terminal window, the output was:

$ ./zombie
2443: going to sleep for a while - child 2444 might die while I snooze
2444: committing suicide (parent 2443)
2443: awake
$

In another terminal window, running ps -f produced:

  UID   PID  PPID   C STIME   TTY           TIME CMD
  503   260   249   0 12:42PM ttys004    0:00.08 -bash
  503  2443   260   0  5:11PM ttys004    0:00.00 ./zombie
  503  2444  2443   0  5:11PM ttys004    0:00.00 (zombie)

The parenthesize (zombie) is the defunct process, and the name in parentheses is the original name of the process. When I copied the program to living-dead, the corresponding output was:

  UID   PID  PPID   C STIME   TTY           TIME CMD
  503   260   249   0 12:42PM ttys004    0:00.09 -bash
  503  2454   260   0  5:13PM ttys004    0:00.00 ./living-dead
  503  2455  2454   0  5:13PM ttys004    0:00.00 (living-dead)

(On most systems, the defunct process is marked as <defunct> or something similar.)

Clearly, the value in the PPID column identifies the parent process of the zombie, and the various process IDs match the output from the programs themselves.

Answer 2

You can find out who birthed that undead process by running ps ef or using htop.

PID   TTY      STAT   TIME COMMAND
21138 tty1     T      0:00 sudo /usr/bin/aura -Akax open_watcom openwatcom-extras-hg HOME=/home/hav3lock USER=hav3lock SHELL=/bin/zsh TERM=linux PATH=/usr/local/sbin:/u
21139 tty1     T      0:00  \_ /usr/bin/aura -Akax open_watcom openwatcom-extras-hg TERM=linux PATH=/usr/local/sbin:/usr/local/bin:/usr/bin:/usr/bin/site_perl:/usr/bin/
22111 tty1     Z      0:00      \_ [su] <defunct>`

In the above I have a zombie process who's momma is /usr/bin/aura, a process spawned by sudo /usr/bin/aura.

Running sudo kill -9 21138 will kill the parent, thereby subsequently killing its zombie spawn.

PID   TTY      STAT   TIME COMMAND
23858 pts/9    S+     0:00 sudo sudo ps ef LANG=en_US.utf8 DISPLAY=:0 SHLVL=3 LOGNAME=hav3lock XDG_VTNR=1 PWD=/home/hav3lock/sy.l/repos/pub_rel/slen/linux/src HG=/usr/b
23860 pts/9    S+     0:00  \_ sudo ps ef LANG=en_US.utf8 DISPLAY=:0 LS_COLORS=no=0:fi=0:di=34:ln=00;96:or=91;4:mi=00;31;9:mh=01;37:pi=33;7:so=01;35:do=35:bd=01;33:cd=9
23861 pts/9    R+     0:00      \_ ps ef LANG=en_US.utf8 DISPLAY=:0 LS_COLORS=no=0:fi=0:di=34:ln=00;96:or=91;4:mi=00;31;9:mh=01;37:pi=33;7:so=01;35:do=35:bd=01;33:cd=93
13405 tty2     S<sl+   3:49 X :0 HOME=/home/hav3lock USER=hav3lock SHELL=/bin/zsh TERM=linux PATH=/usr/local/sbin:/usr/local/bin:/usr/bin:/usr/bin/site_perl:/usr/bin/ve`