This document discusses daemons and init services in Linux. It begins by introducing daemons as processes that run in the background and are started during system bootup. It describes the basic structure of daemons, including forking, changing file permissions, and closing standard file descriptors. It also discusses how daemons can be controlled through start, stop, reload commands. The document then explains that init is the parent process that starts other processes during boot according to runlevels, and describes the different runlevels like single-user mode or full multiuser mode with networking.

1. Daemons And Init Services In
Linux
OMKAR M. BHAGAT
LINUX

2. Objectives
 Introduction Of Daemons .
 Basic Structure Of Daemons .
 Controls Of Daemons .
 About Init Services .
 Runlevels In Linux .
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3. Introduction Of Daemons
 Daemons are processes that 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,
they run in the background.
 Linux systems have numerous daemons that
perform day-to-day activities.
 Typically daemons have names that end with
the letter “d” : for example syslogd.
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4. Basic Structure Of Daemons
 Fork off the parent process.
 Change file mode mask (umask).
 Open any logs for writing.
 Create a unique Session ID (SID).
 Change the current working directory to a safe
place.
 Close standard file descriptors.
 Enter actual daemon code.
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5. Controls Of Daemons
 Service daemon start –To start the daemon
process .
 Service daemon status –To know the status of
daemon.
 Service daemon reload –To restart the daemon
process.
 Service daemon stop –To stop the daemon
process.
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6. About Init Services
 Init is the root/parent of all processes executing
on Linux.
 The first processes that init starts is a script
/etc / rc.d / rc.sysinit.
 Based on the appropriate run-level, scripts are
executed to start various processes to run the
system and make it functional.
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7. Runlevels In Linux
 A run level is a state of init and the whole
system that defines what system services are
operating.
 Run levels are identified by numbers.
 Some system administrators use run levels to
define which subsystems are working,
e.g., whether X is running, whether the network
is operational, and so on.
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8. Runlevels In Linux
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 0 - Halt the system.
 1 - Single-user mode (for special administration).
 2 - Local Multiuser with Networking but without
network service (like NFS).
 3 - Full Multiuser with Networking.
 4 - Not Used.
 5 - Full Multiuser with Networking and X
Windows(GUI).
 6 – Reboot.

9. THANK YOU
OMKAR M.BHAGAT