1. UNIX Services and Daemons

2. Overview
Daemons are:
background processes that perform a system-related task
are independent processes rather than part of the kernel
started at boot time or when there is a need for them.
The historical meaning of the word daemon is: an independent spirit, nor good or evil. To quote from the Handbook “UNIX systems seem to be infested with both daemons and demons.”

3. Essential daemons Init (don’t play with it if you are not an expert).
is the first process to start after boot and places the system in single user mode of spawns a shell to read the startup files
you can re-start the system by sending SIGHUP to init.
cron
runs commands at preset times
accepts crontabs (schedule files) from both users and administrators
inetd
is a daemon that manages other daemons
only works with network daemons

4. inetd.conf and services
/etc/inetd.conf
list the services name, type of socket (stream=TCP), protocol (tcp or udp), requests (multiple=wait), username to run, fully qualified path name of daemon. See example.
/etc/services
list the services name, port/protocol, alias. See example.
It is used by inetd to assign ports.

5. The cron daemon It starts at boot and remains up.
Almost anything you can do in a shell window can be done in cron.
SGI: /etc/cron.d directory for defaults (deny, allow) and /usr/var/spool/cron directory for crontabs.
Crontabs are the scheduling files. See an example here. Are created by user, e.g. root, abento, etc.
format: min hour daymo month daywk cmd