Daemons

ro:Daemon zh-CN:Daemon A daemon is a program that runs in the background, waiting for events to occur and offering services. A good example is a web server that waits for a request to deliver a page or a ssh server waiting for someone trying to log in. While these are full featured applications, there are daemons whose work is not that visible. Daemons are for tasks like writing messages into a log file (e.g. syslog, metalog) or keeping your system time accurate (e.g. ntpd).

Note: The word daemon is sometimes used for a class of programs that are started at boot but have no process which remains in memory. They are called daemons simply because they utilize the same startup/shutdown framework (e.g. /etc/rc.d/ scripts) used to start traditional daemons. For example, the /etc/rc.d scripts for alsa and cpufreq provide persistent configuration support for their perspective kernel modules but do not start additional background processes to service requests or respond to events.

From the user's perspective the distinction is typically not significant unless the user tries to look for the "daemon" in a process list.

Starting on Boot

A default install of Arch Linux will leave you with very few services (or daemons) enabled during boot. You can add or remove services by editing the DAEMONS array in your rc.conf file. It will initially look something like this:

DAEMONS=(syslog-ng network netfs crond)

They will start in the order you have them listed. You can disable one and keep it in the array by prefixing it with an exclamation mark (!). You can also have them start in the background by adding the @ symbol in front of it.

Daemon scripts are stored in /etc/rc.d/. You can print the list of all the available daemons on your system, along with their current status, with:

$ rc.d list

Performing daemon actions manually

Every daemon has a series of actions that can be called with specific commands: usually there are at least start, stop, and restart. You can issue each with:

# /etc/rc.d/daemon-name {start|stop|restart|...}

A completely equivalent way is:

# rc.d {start|stop|restart|...} daemon-name-1 daemon-name-2 daemon-name-3 ...

which, as it is clear from the example, works also with a list of daemons, calling for each the given action.

For a list of all the available commands for a specific daemon, check its documentation, or just open the script in a text viewer.

Essentials

You do not have to add any more services, if you do not feel the need. However, a typical desktop user will add at least CUPS and dbus. As you install new services, you will have to manually add them to the DAEMONS array in /etc/rc.conf (located at the very end).

Starting Daemons in Background

This is helpful for starting a service and letting the next service start before the previous one has finished. Which services to start background depends on your needs. Do not background anything you need immediately. Here is an example:

DAEMONS=(syslog-ng gensplash dbus network netfs @avahi-daemon @samba @crond @openntpd @cupsd @mpd)

Starting openntpd in the background could lead to synchronization errors between the actual time and the time stored on your computer. If you recognize an increasing time difference between your desktop clock and the actual time, try to start the openntpd daemon normally and not in the background.

rc.conf GUI front-ends

rc.conf GUI front-ends allow one to easily change settings in /etc/rc.conf using a graphical application.

List of Daemons

Here is a list of daemons. Note that any package can provide a daemon, so this list will never be complete. Please feel free to add any missing daemons here, in alphabetical order. For each daemon the name of the script (for initscripts) and of the service (for systemd) is given.

Initscripts	Systemd	Description
acpid	acpid.service	Delivers ACPI events.
alsa	alsa-store.service alsa-restore.service	Advanced Linux Sound Architecture; provides device drivers for sound cards.
atd	not yet implemented	Run jobs queued for later execution.
avahi-daemon	avahi-daemon.service	Allows programs to automatically find local network services.
avahi-dnsconfd	avahi-dnsconfd.service
clamav	clamd.service freshclamd.service	Antivirus.
cpupower	cpupower.service	Userspace tools for the kernel cpufreq subsystem
craftbukkit	not yet implemented	CraftBukkit Minecraft server
crond	cronie.service	Daemon to schedule and time events. The daemon name crond is used by at least two packages, cronie and dcron.
cupsd	cupsd.service or cups.service	Common UNIX Printing System daemon.
dbus	dbus.service	Message bus system for software communication.
dropboxd	not yet implemented	Cross-platform file synchronisation with version control.
fam	deprecated	File Alteration Monitor. (deprecated)
fancontrol	fancontrol.service	Fan control daemon (part of lm_sensors)
fbsplash	not yet implemented	Graphical boot splash screen for the user.
ftpd	not yet implemented	Inetutils ftp daemon
gdm	gdm.service (in community/systemd-arch-units)	Gnome Display Manager (Login Screen)
git-daemon	not yet implemented	GIT daemon
gpm	gpm.service	Console mouse support.
hal	deprecated	Hardware Abstraction Layer. (Deprecated)
hddtemp	hddtemp.service	Hard drive temperature monitor daemon
healthd	healthd.service	A daemon which can be used to alert you in the event of a hardware health monitoring alarm (part of lm_sensors).
iptables	iptables.service	Load firewall rules.
ip6tables	ip6tables.service	Load firewall rules for ipv6.
httpd	not yet implemented See Systemd/Services#apache2 for manual configuration.	Apache HTTP Server (Web Server)
hwclock		Not a daemon as such, but on shutdown, updates hwclock to compensate for drift. Only run this daemon if ntpd is not running as both daemons adjust the hardware clock.
irqbalance	not yet implemented	Irqbalance is the Linux utility tasked with making sure that interrupts from your hardware devices are handled in as efficient a manner as possible.
kdm	kdm.service	KDE Display Manager (Graphical Login)
krb5-kadmind	krb5-kadmind.service	Kerberos 5 administration server
krb5-kdc	krb5-kdc.service	Kerberos 5 KDC
krb5-kpropd	krb5-kpropd.service	Kerberos 5 propagation server
laptop-mode	laptop-mode-tools.service	Laptop Power Saving Tools
lighttpd	lighttpd.service	Lighttpd HTTP Server (Web Server).
mdadm	mdadm.service	MD Administration (Linux Software RAID).
mpd	mpd.service	Music Player Daemon.
mysqld	mysqld.service	MySQL database server.
netfs	unused, handled automatically, see remote-fs.service to manually execute scripts	Mounts network file systems.
net-auto-wired	net-auto-wired.service	Netcfg replacement for network - connects to wired network
net-auto-wireless	net-auto-wireless.service	Netcfg replacement for network - connects to wireless network
net-profiles	netcfg.service	Netcfg replacement for network - connects to profiles
network	(dynamic Ethernet) dhcpcd@.service	To bring up the network connections.
networkmanager	NetworkManager.service NetworkManager-wait-online.service	Replaces network, and provides configuration and detection for automatic network connections.
nginx	nginx.service	Nginx HTTP Server and IMAP/POP3 proxy server (Web Server)
nscd	nscd.service	Name service cache daemon
ntpd	ntpd.service	Network Time Protocol daemon (client and server).
openntpd	openntpd.service	alternate Network Time Protocol daemon (client and server).
php-fpm		FastCGI Process Manager for PHP
postgresql	postgresql.service	PostgreSQL database server.
powernowd	not yet implemented	To adjust speed of CPU depending on system load. See also CPU Frequency Scaling
ppp	not yet implemented	A daemon which implements the Point-to-Point Protocol for dial-up networking.
preload	preload.service	Makes applications run faster by prefetching binaries and shared objects.
pure-ftpd	not yet implemented	FTP server.
readahead	systemd-readahead-collect.service systemd-readahead-done.service systemd-readahead-drop.service systemd-readahead-replay.service	Readahead for faster boot
rfkill	rfkill.service	(Un)block radio devices. (.service does not seem to provide equivalent functionality.)
rsyncd	rsyncd.service	Rsync daemon.
rsyslogd	rsyslog.service	The latest version of a system logger.
samba	smbd.service nmbd.service winbindd.service	File and print services for Microsoft Windows clients.
saned	saned@.service	To share the scanner system over network.
sensord	sensord.service	Sensor information logging daemon (part of lm_sensors)
sensors	lm_sensors.service	Hardware (temperature, fans etc) monitoring.
slim	slim.service	Simple Login Manager
smartd	smartd.service	Self-Monitoring, Analysis, and Reporting Technology (S.M.A.R.T) Hard Disk Monitoring
snmpd	not yet implemented	A suite of applications used to implement SNMP
soundmodem	not yet implemented	Multiplatform Soundcard Packet Radio Modem
sshd	sshd.service sshd@.service sshdgenkeys.service	OpenSSH (secure shell) daemon.
stbd	deprecated	This daemon was previously necessary for gnome-system-tools. However, as of gnome-tools 2.28, it is no longer needed.
svnserve	svnserve.service	Subversion server
syslogd	deprecated	This was the older and basic system logger.
syslog-ng	syslog-ng.service	System logger next generation.
timidity++	not yet implemented	Software synthesizer for MIDI.
vboxservice	vboxservice.service	VirtualBox Guest Service
vsftpd	vsftpd.service vsftpd@.service vsftpd-ssl.service	FTP server.
wicd	wicd.service	Combine with dbus to replace network, a lightweight alternative to NetworkManager.
x11vnc	not yet implemented	VNC remote desktop daemon

See also

• Initscripts
• Systemd
• Examples for writing rc.d scripts
• Examples for writing Systemd/Services