Zombie process - Definition

On Unix systems a zombie process is a process that has completed execution but the exit status of which has not been read by the parent process yet. In the term's colorful metaphor, the process has died but has not yet been reaped.

The book-keeping information for the zombie has to be retained so it can eventually be supplied to the parent when it does a "wait" system call. After the parent's wait call (or in the lack of a wait call, after the parent terminates), the zombie process will be removed. Typically, zombies that exist for more than a short period of time indicate a bug somewhere.

A zombie process is not the same as an orphan process. Orphan processes don't become zombie processes; instead, they are adopted by init (process ID 1), and init will usually do a "wait" system call for them.

The term zombie process takes its meaning from the common definition of zombie–an undead person.