Daemon Processes

Posted on September 6th, 2006 by Neo.
Categories: Linux, Open Source.

Daemons are processes that live for a long time. They are often started when the system is bootstrapped and terminate only when the system is shut down. Because they don’t have a controlling terminal, we say that they run in the background. UNIX systems have numerous daemons that perform day-to-day activities.

Anything with a parent process ID of 0 is usually a kernel process started as part of the system bootstrap procedure. (An exception to this is init, since it is a user-level command started by the kernel at boot time.) 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.

Process 1 is usually init.. It is a system daemon responsible for, among other things, starting system services specific to various run levels. These services are usually implemented with the help of their own daemons.

Some of the Daemon processes are:

    kevenTD: provides process context for running scheduled functions in the kernel.

  bdflush and kupdated : The Linux kernel flushes cached data to disk The bdflush daemon flushes dirty buffers from the buffer cache back to disk when available memory reaches a low-water mark. The kupdated daemon flushes dirty pages back to disk at regular intervals to decrease data loss in the event of a system failure.

The cron daemon: (crond) executes commands at specified dates and times.

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