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| ~-[[DebianWiki/EditorGuide#translation|Translation(s)]]: English-~ | ~-[[DebianWiki/EditorGuide#translation|Translation(s)]]: English - [[fr/Daemon|Français]] - [[it/Daemon|Italiano]]-~ |
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| A [[WikiPedia:Daemon_(computing)|daemon]], or system service, is a background process usually started during the initial boot sequence by [[init]]. Daemons typically run independent of users, waiting for system events to occur and providing services in response. Some common daemons include: | A [[WikiPedia:Daemon_(computing)|daemon]], or system service, is a background process usually started during the boot sequence. Daemons typically run independent of users, waiting for events to occur and providing services in response. Some common daemons include: |
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| == Daemons in Debian == Debian makes use of [[WikiPedia:Init#SysV-style|System V]]-style init scripts for daemon management. This allows daemons to operate conditionally, based on the current RunLevel of the computer. For example, a daemon can be configured to run only when the computer is in single-user mode (runlevel 1) or, more commonly, when in multi-user mode (runlevels 2-5). For more information, see [[init]] and [[RunLevel]]. |
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| == Managing Daemons == === A brief introduction to Debian init scripts === Daemon init scripts are stored in {{{/etc/init.d/}}} |
== Daemon management with systemd == Since [[DebianJessie]], [[systemd]] is used to manage daemons. === Common daemon control === Daemons are controlled with the systemctl command: {{{ # systemctl <COMMAND> <NAME> }}} where NAME is the name of the service or daemon. The most common commands for controlling daemons are: * '''start''': starts a service immediately * '''stop''': stops a service immediately * '''restart''': restarts a service * '''reload''': asks a service to reload its configuration * '''status''': shows the current status of a service For instance, the sshd daemon is restarted by {{{ # systemctl restart ssh }}} === Enable/disable daemons === The systemctl command is also used to enable or disable the start of a daemon during system boot: {{{ # systemctl <COMMAND> <NAME> }}} where NAME is the name of the service or daemon. The most important commands to enable/disable daemons are: * '''enable''': enable service to be started during boot sequence * '''disable''': do not start service during boot sequence * '''is-enabled''': check if a service is already enabled Note that the enable/disable commands only affect the system at the next boot. To change the system immediately, use the ''--now'' option. For instance: {{{ # systemctl --now disable ssh }}} will prevent starting sshd at the next boot and stop the daemon immediately. == Daemon management with sysvinit == Before [[DebianJessie]], [[WikiPedia:Init#SysV-style|System V]]-style init scripts were used for daemon management by default. This allows daemons to operate conditionally, based on the current RunLevel of the computer. For example, a daemon can be configured to run only when the computer is in single-user mode (runlevel 1) or, more commonly, when in multi-user mode (runlevels 2-5). For more information, see [[Init]] and [[RunLevel]]. The [[http://www.debian.org/doc/debian-policy/|Debian Policy Manual]] (sections [[http://www.debian.org/doc/debian-policy/ch-opersys.html#s-sysvinit|9.3]] and [[http://www.debian.org/doc/debian-policy/ch-opersys.html#s9.4|9.4]]) is an excellent resource for better understanding daemon init scripts in Debian. === A brief introduction to Debian sysvinit init scripts === Daemon init scripts are stored in {{{/etc/init.d/}}} along with the system's other boot-time init scripts. |
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| To view a list of currently available services: | Daemon init scripts are treated as configuration files by [[dpkg]]. This means they remain on the system after a package is uninstalled, unless the '{{{purge}}}' option is used. === Common daemon controls === Most daemon scripts accept a common set of options, which can be passed directly to the script at the command line, for example: |
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| $ ls /etc/init.d }}} === Common service tasks === Most system services accept a common set of options, which can be passed directly to the daemon script at the command line, for example: {{{ # /etc/init.d/ssh restart |
# service ssh restart |
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| ''Note: Many daemons provide essential services to a working Debian installation; others can pose unnecessary security risks when enabled carelessly. Caution should be used whenever managing daemons. When in doubt, refer to the documentation of the daemon itself.'' | ''Note: When in doubt, refer to the documentation of the daemon itself.'' |
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| Several tools exist to manage system services, including DebianPkg:rcconf and DebianPkg:sys-v-conf. The default tool however is '''update-rc.d''' and that is what the following examples use. | |
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| ==== Enabling services ==== To (re)enable a service, using the default settings, run the following: |
To (re)enable/disable a daemon (using the default settings & runlevels) run the following command, where ''<daemon>'' corresponds to the name of the init script as listed in {{{/etc/init.d/}}}: |
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| # update-rc.d <servicename> defaults }}} ==== Disabling services ==== To disable a service, run the following in a terminal as root: {{{ # update-rc.d -f <servicename> remove |
# update-rc.d <daemon> enable|disable |
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| For more information on Debian's way of managing and writing init scripts see [[LSBInitScripts/DependencyBasedBoot]] and [[LSBInitScripts]]. === GUI utilities for daemon management === Several GUI tools exist to make daemon management even simpler; some popular examples available for Debian include: DebianPkg:rcconf and DebianPkg:sysv-rc-conf. |
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| * [[init]] | * [[Init]] |
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| * manpages: [[DebianMan:5/inittab|inittab]],[[DebianMan:8/init|init]],[[DebianMan:5/rcS|rcS]], [[DebianMan:8/update-rc.d|update-rc.d]], [[DebianMan:8/runlevel|runlevel]] | * manpages: [[DebianMan:5/inittab|inittab]], [[DebianMan:8/init|init]], [[DebianMan:5/rcS|rcS]], [[DebianMan:8/update-rc.d|update-rc.d]], [[DebianMan:8/runlevel|runlevel]], [[DebianMan:8/insserv|insserv]] |
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| ## If this page belongs to an existing Category, add it below. ## CategorySomething | CategoryAnother |
CategoryBootProcess |
Translation(s): English - Français - Italiano
A daemon, or system service, is a background process usually started during the boot sequence. Daemons typically run independent of users, waiting for events to occur and providing services in response. Some common daemons include:
sshd - listens for and manages incoming ?SSH connections
acpid - listens for power management events and executes scripts based on them
apache - provides a local HTTP web server
Contents
Daemon management with systemd
Since DebianJessie, systemd is used to manage daemons.
Common daemon control
Daemons are controlled with the systemctl command:
# systemctl <COMMAND> <NAME>
where NAME is the name of the service or daemon. The most common commands for controlling daemons are:
start: starts a service immediately
stop: stops a service immediately
restart: restarts a service
reload: asks a service to reload its configuration
status: shows the current status of a service
For instance, the sshd daemon is restarted by
# systemctl restart ssh
Enable/disable daemons
The systemctl command is also used to enable or disable the start of a daemon during system boot:
# systemctl <COMMAND> <NAME>
where NAME is the name of the service or daemon. The most important commands to enable/disable daemons are:
enable: enable service to be started during boot sequence
disable: do not start service during boot sequence
is-enabled: check if a service is already enabled
Note that the enable/disable commands only affect the system at the next boot. To change the system immediately, use the --now option. For instance:
# systemctl --now disable ssh
will prevent starting sshd at the next boot and stop the daemon immediately.
Daemon management with sysvinit
Before DebianJessie, System V-style init scripts were used for daemon management by default. This allows daemons to operate conditionally, based on the current RunLevel of the computer. For example, a daemon can be configured to run only when the computer is in single-user mode (runlevel 1) or, more commonly, when in multi-user mode (runlevels 2-5). For more information, see Init and RunLevel.
The Debian Policy Manual (sections 9.3 and 9.4) is an excellent resource for better understanding daemon init scripts in Debian.
A brief introduction to Debian sysvinit init scripts
Daemon init scripts are stored in /etc/init.d/ along with the system's other boot-time init scripts.
When a daemon is enabled or disabled, symbolic links targeting the respective init script are created or removed under the various /etc/rc*.d/ directories, corresponding to the RunLevel(s) in which the daemon is to run.
Daemon init scripts are treated as configuration files by dpkg. This means they remain on the system after a package is uninstalled, unless the 'purge' option is used.
Common daemon controls
Most daemon scripts accept a common set of options, which can be passed directly to the script at the command line, for example:
# service ssh restart Restarting OpenBSD Secure Shell server: sshd.
A brief description of the most common options follows:
start: start a service
stop: stop a service
restart: restart a service without reloading its job config file
reload: send a SIGHUP signal to running process
status: return the status of a service
Starting and stopping daemons in this manner is temporary and will not survive a reboot. Refer to the next section to enable/disable daemons on a permanent basis.
Enable/disable daemons
Note: When in doubt, refer to the documentation of the daemon itself.
To (re)enable/disable a daemon (using the default settings & runlevels) run the following command, where <daemon> corresponds to the name of the init script as listed in /etc/init.d/:
# update-rc.d <daemon> enable|disable
For more detail on what these commands do, refer to the update-rc.d manpage.
For more information on Debian's way of managing and writing init scripts see LSBInitScripts/DependencyBasedBoot and LSBInitScripts.
GUI utilities for daemon management
Several GUI tools exist to make daemon management even simpler; some popular examples available for Debian include: rcconf and sysv-rc-conf.