Download Core System Services

Core System Services
INIT Daemon
• The init process is the patron of all processes.
• first process that gets started in any Linux/
UNIX -based system.
INIT
• Start up system run level.
• Specify processes to be executed during
system boot.
• Specify processes to be run when the
specified run level is entered.
• Specify certain actions or processes to be run
if certain signals or user actions are indicated.
upstart
• upstart is an event-based replacement for the
init daemon which handles starting of tasks
and services during boot, stopping them
during shutdown, and supervising them while
the system is running
Run level
• A runlevel is a preset operating state on a
Unix-like operating system.
• A system can be booted into any of several
runlevels, each of which is represented by a
single digit integer. Each runlevel designates a
different system configuration and allows
access to a different combination of processes
Run Levels in Linux
Run Level
Description
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 , command line.
4
User Defined
5
Full Multiuser with Networking and X Windows(GUI)
6
Reboot.
The /etc/inittab File
• The /etc/inittab file contains all the
information init needs for starting runlevels.
INETD
• The role of inetd is to function as a “superserver” to other network server–related
processes, such as telnet, ftp, tftp, etc.
• So instead of constantly maintaining potentially
dozens of services loaded in memory waiting to
be used, they are all listed in inetd’s configuration
file, /etc/inetd.conf. On their behalf, inetd listens
for incoming connections. Thus, only a single
process needs to be in memory.
INETD
• low-volume services (such as tftp) are usually
best run through the inetd, whereas highervolume services (such as web servers) are
better run as a stand-alone process that is
always in memory, ready to handle requests
XINETD
• xinetd, the eXtended InterNET Daemon, is an
open-source daemon which runs on many
Linux and Unix systems and manages Internetbased connectivity. It offers a more secure
extension to or version of inetd, the Internet
daemon.
syslogd Daemon
• Syslogd provides two system utilities which
provide support for system logging and kernel
message trapping. Support of both internet
and unix domain sockets enables this utility
package to support both local and remote
logging.
• The syslog daemon processing is controlled by
a configuration file called /etc/syslog.conf in
which you define logging rules and output
destinations for error messages, authorization
violation messages, and trace data.
THE CRON PROGRAM
• The cron program allows any user in the
system to schedule a program to run on any
date, at any time, or on a particular day of
week, down to the minute.
• Using cron is an extremely efficient way to
automate your system, generate reports on a
regular basis
CRON
• The tool that allows you to edit entries to be
executed is crontab.