UNIX Services and Daemons

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.”

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

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.

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