Systemd Execution

Flux can optionally execute jobs as transient systemd units, providing cgroup-based resource enforcement and process isolation. This document describes the internal architecture of that integration for developers.

For administrator configuration, see flux-config-systemd(5) and flux-config-exec(5).

The systemd integration consists of three components:

libsdexec

A common C library that abstracts the D-Bus interface to systemd. It translates libsubprocess-style command objects into StartTransientUnit D-Bus calls, manages I/O channels, and tracks unit state.

sdbus module

A broker module that maintains a connection to the user-level systemd D-Bus session. It translates incoming Flux RPCs to D-Bus method calls and translates D-Bus signals into Flux streaming RPC responses. One instance runs per broker rank.

sdexec module

A broker module that implements the sdexec subprocess service, an alternative to the built-in rexec service. It uses libsdexec and sdbus to launch jobs as transient systemd units, multiplex their I/O, and track their lifecycle. One instance runs per broker rank.

When job-exec selects the sdexec service, it issues sdexec.exec RPCs to the sdexec module on each rank of the allocation. sdexec then drives the full unit lifecycle via sdbus and libsdexec, returning streaming responses (started, output, finished) that mirror the libsubprocess client protocol.

• D-Bus Bridge Module
• Systemd Execution Module
• Systemd Client Library