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# SystemD
`afm-system-daemon` is used to:
- Manage users and user sessions.
- Setup applications and services (_CGroups_, _namespaces_, autostart, permissions).
- Use of `libsystemd` for its programs (event management, **D-Bus** interface).
<!-- section-config -->
Domain | Object | Recommendations
------------------ | -------------- | ------------------------------------
Platform-SystemD-1 | Security model | Use Namespaces for containerization.
Platform-SystemD-2 | Security model | Use CGroups to organise processes.
<!-- end-section-config -->
See [systemd integration and user management](http://iot.bzh/download/public/2017/AMM-Dresden/AGL-systemd.pdf) for more information.
## Benefits
- Removal of one privileged process: **afm-user-daemon**
- Access and use of high level features:
- Socket activation.
- Management of users and integration of **PAM**.
- Dependency resolution to services.
- `Cgroups` and resource control.
- `Namespaces` containerization.
- Autostart of required API.
- Permissions and security settings.
- Network management.
<!-- pagebreak -->
## CGroups
Control Groups offer a lot of features, with the most useful ones you can
control: Memory usage, how much CPU time is allocated, how much device I/O is
allowed or which devices can be accessed. **SystemD** uses _CGroups_ to organise
processes (each service is a _CGroups_, and all processes started by that
service use that _CGroups_). By default, **SystemD** automatically creates a
hierarchy of slice, scope and service units to provide a unified structure for
the _CGroups_ tree. With the `systemctl` command, you can further modify this
structure by creating custom slices. Currently, in AGL, there are 2 slices
(**user.slice** and **system.slice**).
## Namespaces
### User side
There are several ways of authenticating users (Key Radio Frequency, Phone,
Gesture, ...). Each authentication provides dynamic allocation of **uids** to
authenticated users. **Uids** is used to ensure privacy of users and **SMACK**
for applications privacy.
First, the user initiates authentication with **PAM** activation. **PAM**
Standard offers highly configurable authentication with modular design like
face recognition, Voice identification or with a password. Then users should
access identity services with services and applications.
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