What is zombie state in Unix?
A zombie process is a process that completed execution but still
in process table. When a process ends, all of the memory and
resources associated with it are deallocated so they can be used by
other processes. However, the process's entry in the process table
remains. The parent can read the child's exit status by executing
the wait system call, at which stage the zombie is removed After
the zombie is removed, its process ID and entry in the process
table can then be reused. However, if a parent fails to call wait,
the zombie will be left in the process table. In some situations
this may be desirable, for example if the parent creates another
child process it ensures that it will not be allocated the same
process ID.