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What are threads and kernel threads?
A kernel thread is the schedulable entity, which means that the system scheduler handles kernel threads. These threads, known by the system scheduler, are strongly implementation-dependent. To facilitate the writing of portable programs, libraries provide user threads.
What are kernel level threads used for?
Advantages of Kernel-Level Threads Multiple threads of the same process can be scheduled on different processors in kernel-level threads. The kernel routines can also be multithreaded. If a kernel-level thread is blocked, another thread of the same process can be scheduled by the kernel.
How are kernel processes different from other processes?
Kernel processes are special and generally exist for the entire lifetime of the system. They run with superuser privileges and have no controlling terminal and no command line. In the (above) sample ps output, kernel daemons has their names in square brackets.
What’s the difference between a daemon and a process?
Process – Process is a running program. At a particular instant of time, it can be either running, sleeping, or zombie (completed process, but waiting for it’s parent process to pick up the return value). A daemon is a background, non-interactive program.
What are the different types of system daemons?
This section describes some common system daemons with the concepts of process groups, controlling terminals, and sessions as described in Chapter 9. The -a option shows the status of processes owned by others. The -x option shows processes that don’t have a controlling terminal.
How are daemons started without a controlling terminal?
None of the daemons has a controlling terminal: the terminal name is set to a question mark. The kernel daemons are started without a controlling terminal. The lack of a controlling terminal in the user-level daemons is probably the result of the daemons having called setsid.