Ansible Role :vertical_traffic_light: Systemd

Table of Contents

• Supported Platforms
• Requirements
• Role Variables
  • Install
  • Config
  • Launch
• Dependencies
• Example Playbook
• License
• Author Information

Ansible role that installs and configures Systemd units: system components and services managed by the Linux systemd system/service manager.

Supported Platforms:

* Debian
* Redhat(CentOS/Fedora)
* Ubuntu

Requirements

systemd is generally considered the de-facto service management tool for Linux distributions and should be included with most OS installations. While typically not a concern, it may be worth noting that Linux kernel >= 3.13 is required by systemd and Linux kernel >= 4.2 is necessary for unified cgroup hierarchy support.

Reference the systemd README for further details.

Role Variables

Variables are available and organized according to the following software & machine provisioning stages:

• install
• config
• launch

Install

[unit_config: <config-list-entry>:] path: (default: /etc/systemd/system)

• load path to systemd unit configuration.

  In addition to /etc/systemd/system (default), unit configs and associated drop-in ".d" directory overrides for system services can be placed in /usr/lib/systemd/system or /run/systemd/system directories.

  Files in /etc take precedence over those in /run which in turn take precedence over those in /usr/lib. Drop-in files under any of these directories take precedence over unit files wherever located. Multiple drop-in files with different names are applied in lexicographic order, regardless of which of the directories they reside in. See table below and consult systemd(1) for additional details regarding path load priority.

Load paths when running in system mode (--system)

Unit Load File Path	Description
/etc/systemd/system	Local configuration
/run/systemd/system	Runtime units
/usr/local/lib/systemd/system	Units installed for local system administration
/usr/lib/systemd/system	Units of installed packages

Load paths when running in user mode (--user)

Unit Load File Path	Description
$XDG_CONFIG_HOME/systemd/user or $HOME/.config/systemd/user	User configuration ($XDG_CONFIG_HOME is used if set, ~/.config otherwise)
/etc/systemd/user	User units created by the administrator
$XDG_RUNTIME_DIR/systemd/user	Runtime units (only used when $XDG_RUNTIME_DIR is set)
/run/systemd/user	Runtime units
$dir/systemd/user for each $dir in $XDG_DATA_DIRS	Additional locations for installed user units, one for each entry in $XDG_DATA_DIRS
/usr/local/lib/systemd/user	User units installed for local system administration
/usr/lib/systemd/user	User units installed by the distribution package manager

Example

 unit_config:
   - name: apache
     path: /run/systemd/system
     Service:
       ExecStart: /usr/sbin/httpd
       ExecReload: /usr/sbin/httpd $OPTIONS -k graceful
     Install:
       WantedBy: multi-user.target

[unit_config: <config-list-entry>:] type: <string> (default: service)

• type of systemd unit to configure. There are currently 11 different unit types, ranging from daemons and the processes they consist of to path modification triggers. Consult systemd(1) for the full list of available units.

Example

 unit_config:
   - name: apache
     type: socket
     Socket:
       ListenStream: 0.0.0.0:8080
       Accept: yes
     Install:
       WantedBy: sockets.target

Config

Configuration of a systemd unit is declared in an ini-style config file. A systemd unit INI config is composed of sections: 2 common amongst all unit types (Unit and Install) and 1 specific to each unit type. These unit configurations can be expressed within the role's unit_config hash variable as lists of dicts containing key-value pairs representing the name, type, load path of the unit and a combination of the aforemented section definitions.

Each configuration section definition provides a dict containing a set of key-value pairs for corresponding section options (e.g. the ExecStart specification for a system or web service [Service] section or the ListenStream option for a web [Socket] section).

[unit_config: <list-entry>:] Unit | <unit-type e.g. Service, Socket, Device or Mount> | Install: <dict> (default: {})

• section definitions for a unit configuration

Any configuration setting/value key-pair supported by the corresponding Systemd unit type specification should be expressible within each unit_config collection and properly rendered within the associated INI config.

The following provides an overview and example configuration of each unit type for reference.

[Service]

Manages daemons and the processes they consist of.

Example

 unit_config:
   # path: /etc/systemd/system/example-service.service
   - name: example-service
     Unit:
       Description: Sleepy service
     Service:
       ExecStart: /usr/bin/sleep infinity
     Install:
       WantedBy: multi-user.target

[Socket]

Encapsulates local IPC or network sockets in the system.

Example

 unit_config:
   - name: docker
     type: socket
     Unit:
       Description: Listens/accepts connection requests at /var/run/docker/sock (implicitly *Requires=* associated docker.service)
     Socket:
       ListenStream: /var/run/docker.sock
       SocketMode: 0660
       SockerUser: root
       SocketGroup: docker
     Install:
       WantedBy: sockets.target

[Mount]

Controls mount points in the sytem.

Example

 unit_config:
   - name: tmp_new
     type: mount
     Unit:
       Description: New Temporary Directory (/tmp_new)
       Conflicts: umount.target
       Before: local-fs.target umount.target
       After: swap.target
     Mount:
       What: tmpfs
       Where: /tmp_new
       Type: tmpfs
       Options: mode=1777,strictatime,nosuid,nodev

[Automount]

Provides automount capabilities for on-demand mounting of file systems as well as parallelized boot-up.

Example

 unit_config:
   - name: proc-sys-fs-binfmt_misc
     type: automount
     Unit:
       Description: Arbitrary Executable File Formats File System Automount Point
       Documentation: https://www.kernel.org/doc/html/latest/admin-guide/binfmt-misc.html
       ConditionPathExists: /proc/sys/fs/binfmt_misc/
       ConditionPathIsReadWrite: /proc/sys/
     Automount:
       Where: /proc/sys/fs/binfmt_misc

[Device]

Exposes kernel devices and implements device-based activation.

This unit type has no specific options and as such a separate [Device] section does not exist. The common configuration items are configured in the generic [Unit] and [Install] sections. systemd will dynamically create device units for all kernel devices that are marked with the "systemd" udev tag (by default all block and network devices, and a few others). To tag a udev device, use TAG+="systemd in the udev rules file. Also note that device units are named after the /sys and /dev paths they control.

Example

# /usr/lib/udev/rules.d/10-nvidia.rules

SUBSYSTEM=="pci", ATTRS{vendor}=="0x12d2", ATTRS{class}=="0x030000", TAG+="systemd", ENV{SYSTEMD_WANTS}="nvidia-fallback.service"

# Will result in the automatic generation of a nvidia-fallback.device file with appropriate [Unit] and [Install] sections set

[Target]

Provides unit organization capabilities and setting of well-known synchronization points during boot-up.

This unit type has no specific options and as such a separate [Target] section does not exist. The common configuration items are configured in the generic [Unit] and [Install] sections.

Example

 unit_config:
   - name: graphical
     path: /usr/lib/systemd/system/graphical.target
     type: target
     Unit:
       Description: Graphical Interface
       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

[Timer]

Triggers activation of other units based on timers.

Example

 unit_config:
   - name: dnf-makecache
     type: timer
     Timer:
       OnBootSec: 10min
       OnUnitInactiveSec: 1h
       Unit: dnf-makecache.service
     Install:
       WantedBy: multi-user.target

[Swap]

Encapsulates memory swap partitions or files of the operating system.

Example

 # Ensure existence of swap file
 mkdir -p /var/vm
 fallocate -l 1024m /var/vm/swapfile
 chmod 600 /var/vm/swapfile
 mkswap /var/vm/swapfile

------------------------------------

 unit_config:
   - name: var-vm-swap
     type: swap
     Unit:
       Description=Turn on swap for /var/vm/swapfile
     Swap:
       What: /var/vm/swapfile
     Install:
       WantedBy: multi-user.target

[Path]

Activates other services when file system objects change or are modified.

Example

 unit_config:
   - name: Repository Code Coverage Analysis trigger
     type: path
     Unit:
       Description: Activate code coverage analysis on modified git repositories
     Path:
       PathChanged: /path/to/git/repo
       Unit: code-coverage-analysis

[Scope]

Manages a set of system or foreign/remote processes.

Scope units are not configured via unit configuration files, but are only created programmatically using the bus interfaces of systemd. Unlike service units, scope units manage externally created processes and do not fork off processes on their own. The main purpose of scope units is grouping worker processes of a system service for organization and for managing resources.

Example

# *This configuration is for a transient unit file, created programmatically via the systemd API. Do not copy or edit.*
 unit_config:
   - name: user-session
     type: scope

     Unit:
       Description: Session of user
       Wants: [email protected]
       Wants: [email protected]
       After: systemd-logind.service systemd-user-sessions.service [email protected] [email protected]
       RequiresMountsFor: /home/user
       Scope:
         Slice: user-1000.slice
      Scope:
         SendSIGHUP=yes
         TasksMax=infinity

[Slice]

Group and manage system processes in a hierarchical tree for resource management purposes.

The name of the slice encodes the location in the tree. The name consists of a dash-separated series of names, which describes the path to the slice from the root slice. By default, service and scope units are placed in system.slice, virtual machines and containers registered with systemd-machined(1) are found in machine.slice and user sessions handled by systemd-logind(1) in user.slice.

See systemd.slice(5) for more details.

[Drop-in]

Provides override capabilities for units.

Example

 unit_config:
   - name: override.conf
     type: conf
     path: "/lib/systemd/system/[email protected]"
     Service:
       ExecStart:
         - ""
         - "-/sbin/agetty -a muru --noclear %I $TERM"
       EnvironmentFile=/path/to/some/file

Launch

[unit_config: <config-list-entry>:] enabled: (default: no)

• whether the service should start on boot

[unit_config: <config-list-entry>:] state: (default: stopped)

• unit activation state

Dependencies

None

Example Playbook

default example (no custom unit configurations specified):

- hosts: all
  roles:
  - role: 0x0I.systemd

service/socket/mount pair:

- hosts: webservers
  roles:
  - role: 0x0i.systemd
    vars:
      unit_config:
      - name: "my-service"
        Unit:
          After: network-online.target
          Wants: network-online.target
          Requires: my-service.socket
        Service:
          User: 'web'
          Group: 'web'
          ExecStart: '/usr/local/bin/my_service $ARGS'
          ExecReload: '/bin/kill -s HUP $MAINPID'
        Install:
          WantedBy: 'multi-user.target'
      - name: "my-service"
        type: "socket"
        Socket:
          ListenStream: '0.0.0.0:4321'
          Accept: 'true'
        Install:
          WantedBy: 'sockets.target'
      - name: "var-data-my_service"
        type: "mount"
        path: "/run/systemd/system"
        Mount:
          What: '/dev/nvme0'
          Where: '/var/data/my_service'
        Install:
          WantedBy: 'multi-user.target'

License

MIT

Author Information

This role was created in 2019 by O1.IO.