Unix foundations

Zombie Processes

• after exit(), process holds only proc structure and is in zombie state until cleaned completely.
• wait() (issued by the parent or the init process)frees the proc structure and completes process exit,
• If the child dies before the parent which does not wait for it, the proc is not released until the system is rebooted.
• Parent can specify that it will not wait for its children

LINUX

• Modular structure – collection of modules, some of them loadable and unloadable on demand,
• Module – object file whose code be linked and unlinked from the kernel at runtime, executed in kernel mode on behalf of the current process
• Loadable module characteristic – Dynamic linking, -- Stackable modules – may serve as libraries when they are referenced by client modules higher up in the hierarchy, and as clients when they reference modules further down the hierarchy.

Linux components

• At user level – tasks (specific to Linux – combine features of processes and threads);
• At kernel level – interacting collection of components;
• Hardware components – in this case IA-64 Intel Itanium architecture

Linux Task Data Structure

• State
• Scheduling information
• Identifiers
• Interprocess communication
• Links
• Times and timers
• File system
• Address space
• Processor-specific context

Linux States of a Process/Thread

• Running
• Interruptable
• Uninterruptable
• Stopped
• Zombie