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51 lines
1.9 KiB
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51 lines
1.9 KiB
Text
[id='understanding-systemd']
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= Understanding systemd
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systemd is a system and service manager for Linux, compatible with SysV and LSB init scripts. systemd provides:
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* Aggressive parallelization capabilities
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* Uses socket and D-Bus activation for starting services
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* Offers on-demand starting of daemons, keeps track of processes using Linux cgroups
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* Supports snapshotting and restoring of the system state
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* Maintains mount and automount points
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* Implements an elaborate transactional dependency-based service control logic.
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The `systemctl` command is the primary tool to manage systemd. It combines the functionality of SysVinit's `service` and `chkconfig` commands into a single tool you can use to enable and disable services permanently or only for the current session.
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systemd manages _units_, which are representations of system resources and services. This following list shows the unit types that systemd can manage:
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service::
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A service on the system, including instructions for starting, restarting, and stopping the service.
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socket::
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A network socket associated with a service.
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device::
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A device specifically managed with systemd.
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mount::
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A mountpoint managed with systemd.
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automount::
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A mountpoint automatically mounted on boot.
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swap::
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Swap space on the system.
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target::
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A synchronization point for other units. Usually used to start enabled services on boot.
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path::
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A path for path-based activation. For example, you can start services based on the state of a certain path, such as whether it exists or not.
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timer::
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A timer to schedule activation of another unit.
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snapshot::
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A snapshot of the current systemd state. Usually used to rollback after making temporary changes to systemd.
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slice::
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Restrivtion of resources through Linux Control Group nodes (cgroups).
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scope::
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Information from systemd bus interfaces. Usually used to manage external system processes.
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