Requires : このユニットが依存するユニット。前のユニットの起動が失敗したら起動しない 1; Wants : このユニットが依存するユニット。前のユニットの起動が失敗しても起動する 1; Conflicts : 指定したユニットと一緒に起動しない [Service] サービスに関する設定。 We see how to set dependencies for a service and how can we specify the commands to be executed when it is started stopped or reloaded. 気になったので、Wants=, Requires=, BindsTo= のそれぞれで、挙動を調べてみました。 環境は CentOS 8 / systemd-239-18.el8_1.1.x86_64 です。 Wants=unitB See systemd.target(5) for details. For example, the foo service might require network connectivity, which means the foo services requires network.target as a dependency. So if your app needs another service, use Requires=.

All other programs are either started directly by systemd or by one of its child processes. This has the effect that a dependency of type Wants= or Requires= is added from the listed unit to the current unit.

WantsやRequiresは不要では無いのですか？ しかし、各種デーモンのServiceUnitを確認すると そのようなケースが散見されます。 Systemdのロジック的に、まずWantsとRequiresを見て 起動するUnit一覧を確認する、みたいな記述をどこかで見た記憶があり、 Defines unit to use as a dependency for the service.

systemd.unit - Unit configuration ... For example, target units will complement all configured dependencies of type Wants= or Requires= with dependencies of type After= unless DefaultDependencies=no is set in the specified units. Unit dependencies are expressed though Requires, Wants, and Conflicts: Requires: A list of units that this unit depends on, which is started when this unit is started That means if network.target is not there or if it fails to start, this unit would be started anyway. If you activate the unit, systemd activates the units listed in Requires as well.

The various type of services and their differences are also discussed.

The real anger against systemd is that it's inflexible by design because it wants to combat fragmentation, it wants to exist in the same way everywhere to do that. 気になったので、Wants=, Requires=, BindsTo= のそれぞれで、挙動を調べてみました。 環境は CentOS 8 / systemd-239-18.el8_1.1.x86_64 です。 Wants=unitB See the description of Wants= and Requires= in the [Unit] section for details. So if your app needs another service, use Requires=. In this tutorial we analyze the structure of systemd ".service" units, and examine the most common options which can be used to modify how the service behaves. After= (and Before=) is used only for ordering, not for dependency management. 4. The program systemd is the process with process ID 1. That means if network.target is not there or if it fails to start, this unit would be started anyway. But the unit as you defined it here has no strict dependencies, only weak (Wants= instead of Requires=). Hot Network Questions Why Not Prune Your Neural Network? What is the difference between Requires, Wants and Conflicts in systemd unit file? Requires : このユニットが依存するユニット。前のユニットの起動が失敗したら起動しない 1; Wants : このユニットが依存するユニット。前のユニットの起動が失敗しても起動する 1; Conflicts : 指定したユニットと一緒に起動しない [Service] サービスに関する設定。 But the unit as you defined it here has no strict dependencies, only weak (Wants= instead of Requires=). Like it or not, systemd is here to stay, so we might as well know what to do with it. tl;dr: make it possible to start the network at any time by starting network-online.target In the initial design, foobar-wait-online.service would have Requisite=foobar.service, so that foobar-wait-online.service could be enabled unconditionally, irrespective of whether foobar.service itself is enabled. Units that require swap to be available can specify this condition using the Wants=, Requires=, and After= specifications to indicate the nature of their relationship. systemd is started directly by the kernel and resists signal 9, which normally terminates processes. Documentation =man:systemd.special (7) Requires =multi-user.target Wants =display-manager.service Conflicts =rescue.service rescue.target After =multi-user.target rescue.service rescue.target display-manager.service AllowIsolate = yes [root @ testvm1 system] #

Systemd: Requires vs wants. The primary result is that the current unit will be started when the listed unit is started. 1. systemd: finish the execution of custom shell script before starting nginx.

Systemd automatically resolves the dependencies and activates the units/services listed in the Wants/Requires statements. 0. systemd service wants/after optional. Requires. The After/Before statements of a unit define the order in which the unit should be started. Systemd starts all units of the system. The After= directive can be used to delay unit activation until another unit is started, such as network, or another service, like mysql.service This doesn’t make it a hard dependant of that service, though you can do that with the Requires= or Wants= directives. A "want" does not need to be fulfilled in order for the unit to start successfully. Getting and Setting the Default Target. The subdirectories in /etc/systemd/system are lists of wants for various targets.

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