Comparison of init systems

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This article compares and contrasts init systems. Some of the init systems compared below are available for Gentoo, while others (like launchd and SMF) are not.

Available software

Feature Init system
sysvinit OpenRC upstart systemd SMF launchd Epoch finit runit s6 + s6-rc BSD rc.d
Supported in Gentoo partially (used by OpenRC) Yes (default init) No Yes No No Yes No Yes No No
Package / Bug# sys-apps/sysvinit sys-apps/openrc bug #498376
sys-apps/upstart in unity-gentoo overlay.
sys-apps/systemd - - sys-apps/epoch - sys-process/runit sys-apps/s6 + sys-apps/s6-rc -
Supported platforms Linux / BSD Linux + BSD Linux Linux Solaris MacOSX Linux Linux Linux / BSD / MacOSX Linux / BSD / MacOSX BSD
Main coding language C POSIX shell (+ C) C C C C C C C C POSIX shell (+ C)
Main dependencies - init (sysv or BSD) D-Bus D-Bus init(sysv?) - libc, /bin/sh ? - skalibs, execline rcorder
Init script/service format single config file shell scripts config files + shell fragments config files (ini) XML (+ shell scripts) plist multiple or single .conf multiple or single .conf shell scripts execline or shell scripts shell scripts
Per-service configuration No Yes (conf.d) With in-job mechanisms (normal exit, respawn) Yes Yes (service instances) ? Yes (v1.1+) ? No No No
Running as a daemon Yes (PID 1) Yes (PID 1) Yes (PID 1) Yes (PID 1) Yes (invoked) Yes (PID 1) Yes (PID 1) Yes (PID 1) Yes (PID 1) Yes (sys-apps/s6-linux-init) Yes (PID 1)
Cross-service dependencies/events No Yes Yes Yes Yes No Yes (basic support, v1.3+) ? Yes Yes Yes
Parallel service startup Yes Yes (optional) Yes Yes Yes Yes No Yes Yes Yes Yes
Keeping daemons alive Yes Yes (optional v0.21+ via supervise-daemon) Yes Yes Yes Yes Yes Yes Yes Yes Yes
Preferred service file supplier n/a Gentoo Ubuntu upstream Solaris MacOSX n/a n/a Void Linux n/a NetBSD, FreeBSD, OpenBSD
License GPL v2+ 2-cl. BSD GPL v2 LGPL v2.1+ ? Apache License 2.0 Unlicense MIT BSD ISC BSD

Supported services (in Gentoo)

Feature OpenRC systemd
Filesystem mounting One script per group (root, local, network, swap...). Two units per mountpoint (fsck + mount), runtime-generated with dependencies.
getty (terminal prompts) Started through /etc/inittab or via agetty script One unit per console, instantiated from template on-demand.
Networking setup Several options[1] like dhcpcd[2][3], netifrc[4], iwd [5], or NetworkManager.[6][7] External (NetworkManager, networkd, DHCP daemons).
X11 Display Manager setup Single service for all (required to auto-restart). Separate DM units.

See also

External resources