is psutil.STATUS_DEAD status same as psutil.STATUS_ZOMBIE?

Question

In python psutil module, I see two status for a process, psutil.STATUS_DEAD and psutil.STATUS_ZOMBIE. I need to understand the difference between both. I am able to simulate Zombie process using kill -1 and kill -3 command, but not able to simulate Dead process.

Any thought here?

Answer 1

They are different as defined in the 'psutil/_commom.py':

STATUS_ZOMBIE = "zombie"
STATUS_DEAD = "dead"

But if you search STATUS_DEAD in version 5.9.0, you may find they may be the same in some sense.

In 'psutil/_psbsd.py' shows that STATUS_DEAD is not used in any BSD platforms

# OPENBSD
        # According to /usr/include/sys/proc.h SZOMB is unused.
        # test_zombie_process() shows that SDEAD is the right
        # equivalent. Also it appears there's no equivalent of
        # psutil.STATUS_DEAD. SDEAD really means STATUS_ZOMBIE.
        # cext.SZOMB: _common.STATUS_ZOMBIE,
        cext.SDEAD: _common.STATUS_ZOMBIE,
        cext.SZOMB: _common.STATUS_ZOMBIE,

In 'psutil/_pslinux.py' about Linux shows:

# See:
# https://github.com/torvalds/linux/blame/master/fs/proc/array.c
# ...and (TASK_* constants):
# https://github.com/torvalds/linux/blob/master/include/linux/sched.h
PROC_STATUSES = {
    "R": _common.STATUS_RUNNING,
    "S": _common.STATUS_SLEEPING,
    "D": _common.STATUS_DISK_SLEEP,
    "T": _common.STATUS_STOPPED,
    "t": _common.STATUS_TRACING_STOP,
    "Z": _common.STATUS_ZOMBIE,
    "X": _common.STATUS_DEAD,
    "x": _common.STATUS_DEAD,
    "K": _common.STATUS_WAKE_KILL,
    "W": _common.STATUS_WAKING,
    "I": _common.STATUS_IDLE,
    "P": _common.STATUS_PARKED,
}

The statuses corresponds to the linux's task states:

// https://github.com/torvalds/linux/blame/master/fs/proc/array.c
static const char * const task_state_array[] = {

    /* states in TASK_REPORT: */
    "R (running)",      /* 0x00 */
    "S (sleeping)",     /* 0x01 */
    "D (disk sleep)",   /* 0x02 */
    "T (stopped)",      /* 0x04 */
    "t (tracing stop)", /* 0x08 */
    "X (dead)",     /* 0x10 */
    "Z (zombie)",       /* 0x20 */
    "P (parked)",       /* 0x40 */

    /* states beyond TASK_REPORT: */
    "I (idle)",     /* 0x80 */
};

Therefore, the difference between them in linux is clear. What Is a “Zombie Process” on Linux?

In psutil, if you create one process p using psutil.Popen(), then kill it. As long as the parent process isn't terminated or you don't call p.wait(), the process will always keep 'Zombie' status.