4380
Comment: Replaced "/etc/init.d/" with modern "service" command
|
← Revision 46 as of 2017-08-19 10:27:16 ⇥
5248
|
Deletions are marked like this. | Additions are marked like this. |
Line 4: | Line 4: |
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: |
Line 11: | Line 11: |
== 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]]. |
== 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]]. |
Line 16: | Line 55: |
== Daemon management == === A brief introduction to Debian init scripts === |
=== A brief introduction to Debian sysvinit init scripts === |
Line 40: | Line 78: |
''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.'' |
Line 42: | Line 80: |
==== Enabling daemons ==== To (re)enable a daemon (using the default settings) run the following command, where ''<daemon>'' corresponds to the name of the init script as listed in {{{/etc/init.d/}}}: |
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/}}}: |
Line 45: | Line 83: |
# insserv <daemon> | # update-rc.d <daemon> enable|disable |
Line 48: | Line 86: |
==== Disabling daemons ==== To disable a daemon at its default runlevels, execute the following command, where ''<daemon>'' corresponds to the name of the init script as listed in {{{/etc/init.d/}}}: {{{ # insserv -r <daemon> }}} |
For more detail on what these commands do, refer to the [[DebianMan:8/update-rc.d|update-rc.d manpage]]. |
Line 54: | Line 88: |
For more detail on what these commands do, refer to the [[DebianMan:8/insserv|insserv manpage]]. These commands assume the daemon's script in /etc/init.d has the appropriate LSB headers. For more information on Debian's new way of enabling/disabling scripts see [[https://wiki.debian.org/LSBInitScripts/DependencyBasedBoot]] and [[https://wiki.debian.org/LSBInitScripts]]. |
For more information on Debian's way of managing and writing init scripts see [[LSBInitScripts/DependencyBasedBoot]] and [[LSBInitScripts]]. |
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.