| Daemon - Daemons are processes
that are started by the UNIX kernel and exist for a specific purpose.
For instance, the lpsched daemon exists for the sole purpose of
handling print jobs. When no printing is taking place on the system,
the lpsched daemon is running but inactive. When a print job is
submitted, this daemon becomes active until the job is finished. The dtlogin
daemon provides the CDE login screen at the beginning of a user's
session and again after the user exits CDE. UNIX daemons are
similar to services in Windows NT/2000 and NetWare Loadable
Modules (NLMs) with Novell NetWare.
Parent - A process which spawns
another process is referred to as its parent. Following system
boot-up, a process called init daemon is invoked. Every process
except init has a parent process. The init daemon is always
process number one. The init process is at the top of the
process hierarchy and is responsible for spawning many system
processes. The dtlogin daemon is spawned by init and
is, therefore, referred to as the parent process of the dtlogin
daemon.
Child - A process which is
spawned by another process is referred to as a child process.
When a user is working in a terminal window in CDE, that terminal's PID
is the Parent Process ID (PPID) of any commands
issued in the terminal. These commands are child processes of the
terminal process. The parent process receives and displays the output
from the child process and then "kills" the process. When
you issue a command from the shell, the shell spawns a child process,
waits for it to execute and when it is finished, control returns to
the shell.
Orphan - If a command is issued
in a terminal window and the window is closed before the command
returns output, that process becomes an orphan. The system
passes the orphan process to init which then becomes the parent
process and terminates the child process.
Zombie (or Defunct) -
Occasionally a child process does not return to the parent process
with its output. This process becomes "lost" in the system.
The only resource this process uses is a slot in the process table; it
cannot be stopped in a conventional manner. This type of process is
called a zombie or defunct process. The only way to kill
a defunct process is to reboot the system.
|