Administration Guide Draft/Daemons

Services and Daemons

Introduction

Services (daemons) are programs that perform useful functions on a system but are not normally started by the user. For example, MySQL runs normally as a service; it is not started every time another service needs to connect to the database. Instead, it is normally always running once configured, unless manually shut down.

Services can be started at other times than at system boot. They may be turned on,off, or restarted without restarting the machine as well as being set to run only at certain run levels.

Run levels are various states the machine can exist in. There are two main run levels most Linux users see. Run level 5 is usually the default for most systems, and presents a full graphical environment. The other is run level 3, which is typically used on servers that don't run a graphical environment, or for trouble shooting and low level system driver installation. Run level 0 is a system halt. Run level 6 is a system reboot. To change run levels, use the init command.

Services and Security

Turn off any service not being used. Leaving a service running that is not used leaves a potential system vulnerability for no benefit. For example, Bluetooth in Fedora is enabled by default. If the system isn't actively connecting to a Bluetooth device, there is no reason to keep the service running. Until recently an ISDN service ran by default. If the system does not use ISDN to connect to the Internet, there is no reason to have it installed and always running. There are several ways to find out what a running system's purpose is. [[The GUI service menus often ]have descriptions.?? On the command line, the command man <service name> produces documentation about most services. The general rule is to leave it running unless it is known what the services does.

Configuring Services

1. In KDE (presumes the kde-admin tools are installed): Click on the Fedora icon in the toolbar on the default desktop, then navigate to Administration > Server Settings > Services.
2. In Gnome, in the toolbar click on System > Server Settings > Services.
3. Give the root password when prompted.

In the KDE services application, clicking on a service produces a description of that service and its status. Services without a check mark are not started at run (boot) time. To prevent a service from running on system start up, uncheck the box next to it.

• To enable a service at start up, check the box.
• To stop a service select it, then click on the Stop button.

In the GNOME services application, the On Demand Services tab is for services that are loaded when a client program calls them. For example, the backup system Amanda only runs when an Amanda client talks to the system.

To save the new configuration, click on the Save button. Failing to save changes means the services do not change start up behavior. Clicking on the Revert button erases all the changes.

Services can be configured to start/not start from the command line using chkconfig. The basic usage of chkconfig is to check the list of services and what run level they start in:

/sbin/chkconfig --list
NetworkManager  0:off   1:off   2:on    3:on    4:on    5:on    6:off
NetworkManagerDispatcher        0:off   1:off   2:off   3:off   4:off   5:off   6:off
acpid           0:off   1:off   2:off   3:off   4:off   5:off   6:off
anacron         0:off   1:off   2:on    3:on    4:on    5:on    6:off
apmd            0:off   1:off   2:on    3:on    4:on    5:on    6:off
atd             0:off   1:off   2:off   3:on    4:on    5:on    6:off
auditd          0:off   1:off   2:on    3:on    4:on    5:on    6:off
autofs          0:off   1:off   2:off   3:on    4:on    5:on    6:off
avahi-daemon    0:off   1:off   2:off   3:on    4:on    5:on    6:off
...

1. Open a terminal window (Applications > Accessories > Terminal)
2. To disable a service such as sendmail:

   su -c 'chkconfig --level 2345 sendmail off'

   This stops sendmail from being started in run levels 2,3,4, and 5.
3. To turn sendmail on for run levels 3 and 5:

   su -c 'chkconfig --level 35 sendmail on'

A full list of chkconfig options is available on the manual page:

man chkconfig

To manually stop, restart, or start a service that wasn't already running, use the service command. This example starts the sendmail service:

su -c 'service sendmail restart'

In the screen capture you see an example of stopping a service that failed. In this case because the service was already stopped. You will also see an example of starting NFS. Notice that not just NFS started. 3 other services started automatically when NFS started. Many services are like this.

There is one final way to edit services.

It is highly recommended to use chkconfig or the GUI tools to modify services, as well as using the service command.

To stop a service, use ps to acquire its PID, then stop the PID using the kill command. To modify the stop/start of a service in a particular run time level, edit the /etc/rc files:

ls -d /etc/rc*
rc          rc1.d/      rc3.d/      rc5.d/      rc.d/       rc.sysinit
rc0.d/      rc2.d/      rc4.d/      rc6.d/      rc.local

Each directory corresponds with the same numbered run time level. To start a service for run time level 5, add a link in the /etc/rc5.d/ directory to the corresponding start script in /etc/init.d. The S and K prefix with a number refers to the order in which that service is started or stopped when the system is starting up or shutting down.

These last methods are recommended only for experienced users. On rare occasions it is necessary to modify these files to change default behavior. Generally, an administrator never has to directly touch these files.

xinetd-Based Services

Many services run as sub-services managed by the xinetd service. FTP servers, backup servers, rsync, and a host of others. To enable or disable these services, use the chkconfig command as with init based services.

A default configuration of xinetd services is:

/sbin/chkconfig --list
...
xinetd based services:
amanda:         off
amandaidx:      off
amidxtape:      off
apgd:           off
chargen-dgram:  off
chargen-stream: off
csync2:         off
cups-lpd:       off
cvs:            off
daytime-dgram:  off
daytime-stream: off
discard-dgram:  off
discard-stream: off
echo-dgram:     off
echo-stream:    off
eklogin:        off
ekrb5-telnet:   off
gssftp:         off
klogin:         off
krb5-telnet:    off
kshell:         off
ktalk:          off
rsync:          off
tcpmux-server:  off
time-dgram:     off
time-stream:    off

For example, to turn on the xinetd service for rsync, use the following command:

/sbin/chkconfig rsync on

Then reload the service's configuration with the command su -c 'service xinetd reload'.

Re-issueing the /sbin/chkconfig --list command you now see

/sbin/chkconfig --list | grep rsync
rsync:          on

To customize the configuration of an xinetd service, edit the file for that service in the /etc/xinetd.d directory. For more information on the syntax of these configuration files, refer to the man page for xinetd.conf(5).

Common Services

Some services commonly found on Fedora installations.

Service	Description
Amanda BackupPC	Backup software
abrt	Automatic Bug-Reporting Tool.
acpid	Advanced Configuration and Power Interface daemon which controls and allows interfacing to power management and certain input devices..
amd	Runs the automount daemon for remote filesystem mounting such as nfs.
anacron and crond	Runs certain programs at specified times.
apmd	Monitors laptop battery power and shuts down if power gets too low.
atd	at scheduler. Automatically runs programs/scripts that meet certain criteria.
auditd	System audit daemon
autofs	Used to automatically mount filesystems listed in fstab.
avahi-daemon, avahi-dnsconfd	Supports Apple's Zeroconf protocol.
bluetooth	Provides Bluetooth functionality.
btseed, bttrack	Bittorrent related utils.
cfenvd, cfexecd, cfservd	Part of the cfengine services. cfengine is a system configuration an anomaly detection.
cman	Cluster manager
cpuspeed	System sensor and CPU speed adjustment.
cups	Printing support
dbmail, Postfix, Sendmail, spamassassin, dovecot	Email services and spam protection.
dc_client, dc_server	Caching services
denyhosts	Log watcher that bans hosts with too many failed login attempts.
dhcdbd	Allow systems to use a DHCP server to obtain an IP address.
dund	Bluetooth dial-up networking
firstboot	Used after installation for post-installation configuration. You should turn this off after these configurations are complete.
gpm	Mouse support on the console
haldaemon	Hardware detection layer
hidd	Bluetooth HID daemon
hplip	HP Linux Imaging and Printing
httpd	Apache web server
ip6tables and iptable	Firewall
ipsec	IPsec encryption/authentication
irda	Provides infrared device services.
irqbalance	Distributes hardware interrupts across processors on a multi-processor system.
isdn	Provides ISDN functionality.
jexec	This is provided as a helper to directly run java JAR applications. This is will be included if you installed Sun Java. It is not necessary and can be disabled.
kdump	kexec based crash dumping mechanism for Linux.
kudzu	Looks for new hardware at boot. Runs only at boot time.
ldap	LDAP server
lirc	Linux infrared support
lisa	Network discovery and protocols
lm_sensors	Support for hardware sensors such as CPU temp.
lpd	local printer services
lvm2-monitor	This is a monitoring application for your LVM (Logical Volume Management) system. This is recommended if you use LVM, however if you use manually partition your drives it can be disabled.
mcstran	SELinux related
mdmonitor	Software RAID support. Turn off if you are not using it.
mdmpd	Multipath device support
messagebus	App to app communications
multipathd	failover and multipath support
microcode_ctl	Support for IA32 (Intel PII and newer) microcode
mysqld, Postgresql, Oracle	Database servers
named	Bind DNS server
netfs	Mounts NFS, SMB and other remote filesystems.
netplugd	Linux networking related services
network	Brings up the network.
nfs, nfslock	Provides NFS services.
nscd	Name service cache daemon
ntpd	Syncs your computer clock with time servers.
openais	Clustering, failover, checkpointing and related API.
pand	BlueZ Bluetooth PAN daemon
pcmcia	Provides pcmcia support. May be safely stopped if you are not using a laptop.
pcscd	Smart card support
portmap	Support for port mapping and RPC.
psacct	Monitors system activity and provides audit trail of user actions.
pxe	Provides pxe support. (Preboot execution environment)
raduisd	Provides radius VPN support.
random	Kernel random number generator.
rdisc	Network discovery daemon
readahead_early, readahead_later	Used in speeding up boot time.
restorecond	Sets default SELinux context on new files.
rpcgssd, rpcidmap, rpcsvcgssd	Network file-sharing support
rsync	rsync run as a service. Synchronises files mostly between remote systems.
saslauthd	SASL authentication server
sgi_fam	File alteration monitor
smartd	Watches hard-drives for problems.
smb	Samba server
snmpd, snmtrapd	Linux SNMP support
squid	Proxy server
sshd	SSH server
syslog	System logging service
sysstat	Starts special system logging services.
tux	Tux web server
vncserver	VNC server
vsftpd	FTP server
winbind	Maps Windows domain databases to UNIX
wpa_supplicant	WPA (Wi-Fi Protected Access) supplicant for Linux
xend, xendomains, VMware, libvirtd	Provides a virtual machine.
xfs	X Font Server
ypbind	YP/NIS support
yum-updatesd	Automatic yum updates