Freedom251 › Process Monitoring Software
s6
What s6 is
s6 is a free suite of UNIX programs for supervising processes and managing services on POSIX-compliant systems. Its supervision system maintains a tree of services, provides process controls, and monitors service states. It can notify other services when a service is ready, which can support dependency management. The suite includes s6-log and utilities for syslog-like functions, along with access-control tools and controlled privilege gain without setuid programs. For socket activation, s6 can hold file descriptors without requiring changes to application code, a special library, or a different init system. Related projects include s6-linux-init, s6-rc, s6-frontend, and s6-overlay for Docker images. s6 is free software under the ISC license. Installation requires a POSIX-compliant system, a standard C development environment, and GNU make 3.81 or later. Building requires skalibs 2.15.1.0 or later; execline is recommended for full functionality. The maker provides self-contained documentation and lists a supervision mailing list, an OFTC IRC channel, and a contact email.
Who it suits
s6 suits administrators and developers managing processes and services on POSIX-compliant systems. It is free software, but building it requires a C development environment and specific dependencies.
What it does well
- Maintains and monitors a supervision tree
- Provides service readiness notifications
- Includes logging and access-control utilities
- Supports socket activation with held file descriptors
- Available under the ISC license
What to know first
- Requires a POSIX-compliant system
- Building requires skalibs 2.15.1.0 or later
- GNU make 3.81 or later is required
Limits
The free s6 plan is listed as free. Installation requires a POSIX-compliant system, a standard C development environment, and GNU make 3.81 or later; building requires skalibs 2.15.1.0 or later, with execline recommended for full functionality.
Plans
| Plan | Billed and limits | Price |
|---|---|---|
| s6 | Free software · ISC license · POSIX-compliant system required | Free |
As skarnet.org lists them, read 9 Oct 2026. The maker's own page has the final word.
Getting started
- Visit the s6 website.
- Use a POSIX-compliant system with a standard C development environment.
- Ensure GNU make 3.81 or later is available.
- Obtain skalibs 2.15.1.0 or later to build s6; add execline for recommended full functionality.
- Use the source repository or a listed Codeberg, GitHub, or SourceHut mirror.
Verdict
s6 offers process supervision, service controls, readiness notifications, and logging utilities as free software. Review its system and build requirements before choosing it.
Questions
How much does s6 cost?
The listed s6 plan costs nothing. s6 is free software under the ISC license.
Which systems does s6 support?
It supports POSIX-compliant systems, including Linux and self-hosted environments.
What does s6 do?
It provides process supervision and low-level administration of processes and services, including process controls and service-state monitoring.
What are the installation requirements?
Installation requires a POSIX-compliant system, a standard C development environment, and GNU make 3.81 or later. Building requires skalibs 2.15.1.0 or later; execline is recommended for full functionality.
Does s6 support service readiness and socket activation?
Yes. It provides readiness notifications that can support dependency management and can hold file descriptors for socket activation without application-code changes.
Where can I find s6 documentation and support?
The maker provides self-contained documentation and lists a supervision mailing list, an OFTC IRC channel, and a contact email on skarnet.org.
Facts from s6's own pages
- Dependencies
- Building s6 requires skalibs 2.15.1.0 or later, and execline is recommended for full functionality. · skarnet.org, 9 Oct 2026
- Distribution
- The maker lists release 2.15.1.0 and provides the source repository plus Codeberg, GitHub, and SourceHut mirrors. · skarnet.org, 9 Oct 2026
- Documentation and support
- The maker provides self-contained documentation, points to a supervision mailing list and an OFTC IRC channel, and lists a contact email on skarnet.org. · skarnet.org, 9 Oct 2026
- Integrations
- Related projects include s6-linux-init, s6-rc, s6-frontend, and s6-overlay for Docker images. · skarnet.org, 9 Oct 2026
- License
- s6 is free software available under the ISC license. · skarnet.org, 9 Oct 2026
- Logging
- Its utilities include s6-log and tools for syslog-like functionality. · skarnet.org, 9 Oct 2026
- Platform requirements
- Installation requires a POSIX-compliant system with a standard C development environment and GNU make 3.81 or later. · skarnet.org, 9 Oct 2026
- Privilege handling
- The suite can provide controlled privilege gain without using setuid programs. · skarnet.org, 9 Oct 2026
- Purpose
- s6 is a small suite of UNIX programs for process supervision and low-level administration of processes and services. · skarnet.org, 9 Oct 2026
- Readiness
- s6 provides reliable service readiness notification, which can serve as the basis for service dependency management. · skarnet.org, 9 Oct 2026
- Security
- The s6 page describes the suite as small and secure and lists utilities for access control and privilege handling; it does not state a security certification. · skarnet.org, 9 Oct 2026
- Service control
- Its supervision system maintains a supervision tree and provides tools to control processes and monitor service states. · skarnet.org, 9 Oct 2026
- Socket activation
- s6 supports fd-holding for socket activation without requiring application code changes, linking servers to a specific library, or switching init systems. · skarnet.org, 9 Oct 2026
Where s6 stands on Freedom251
- Process Monitoring Software#20 of 26