An important aspect for all the services is how they are started up. FC6 includes a series of utilities for managing the service daemons (including the network ones). As we have seen on the chapter on local administration, the runlevel is the operating mode that will specify which daemons will be executed. In FC we can find: runlevel 1 (single user), runlevel 2 (multiuser), runlevel 3 (multiuser with network), runlevel 5 (X11 plus /runlevel 3). Typically, we would execute runlevel 5 or 3 if we do not need any graphical interfaces. In order to determine the level that is being executed, we can use /sbin/runlevel, and to know which level will start up by default cat /etc/inittab | grep :initdefault:which will give us information such as id:5:initdefault: (we can also edit /etc/inittab to change the default value.)
To visualise the services that are executing, we can use /sbin/chkconfig –list and to manage them, we can use system-config-services in the graphic mode or ntsysv in the command line. To enable individual services, we can use chkconfig; for example the following command enables the crond service for levels 3 and 5: /sbin/chkconfig --level 35 crond on. Regardless of how the services were started up, we can use /sbin/service –status-all or individually /sbin/service crond status to see the status of each service. And we can also manage this (start, stop, status, reload, restart), for example service crond stop to stop it or service crond restart to restart it.
It is important to not disable the following services (unless you know what you are doing): acpid, haldaemon, messagebus, klogd, network, syslogd. The most important services linked to the network (although this is not an exhaustive list and some have been left out, most of the services are listed here) are:
NetworkManager, NetworkManagerDispatcher: is a daemon with which we can easily change networks (Wifi and Ethernet basically). If we only have one network, it does not have to be executed.
avahi-daemon, avahi-dnsconfd: is an implementation of zeroconf and it is useful for detecting devices and services on local networks without DNS (it is the same as mDNS).
bluetooth, hcid, hidd, sdpd, dund, pand: Bluetooth wireless network is for portable devices (it is not wifi, 802.11). For example, keyboards, mouse, telephones, speakers/headphones etc.
capi, isdn: network based on ISDN hardware.
Iptables: this is the standard firewall service in Linux. It is essential for security if we have a network connection (cable, DSL, T1).
Ip6tables: the same applies but for the protocol and networks based on Ipv6.
netplugd: Netplugd can monitor the network and execute commands when the status changes.
netfs: it is used to automatically mount the file systems through the network (NFS, Samba etc.) during startup.
nfs, nfslock: these are the standard daemons for sharing file systems through the network in Unix/Linux/BSD-type operating systems.
ntpd: server of time and date through the network.
portmap: is a complementary service for NFS (file sharing) and/or NIS (authentication).
rpcgssd, rpcidmapd, rpcsvcgssd: it is used for NFS v4 (new version of NFS).
sendmail: this service can be used to manage the mails (MTA) or support services such as IMAP or POP3.
smb: this daemon makes it possible to share files over Windows systems.
sshd: SSH allows other users to connect interactively and securely to the local machine.
yum-updatesd: FC network updating service.
xinetd: alternative service of inetd that presents a set of features and improvements, such as, for example, launching multiple services through the same port (this service may not be installed by default).