OpenBSD for FreeBSD Users

This quickstart introduces FreeBSD administrators to OpenBSD by mapping familiar concepts to OpenBSD tooling and conventions. It highlights practical differences; it is not an exhaustive comparison nor a discussion of philosophy. The guide assumes OpenBSD 7.8 is already installed and you have command-line access.

Shells #

On OpenBSD, the default shell for both root and regular users is the Korn shell, ksh(1) . This differs from FreeBSD, where the root account defaults to tcsh. OpenBSD’s ksh(1) implements a superset of the traditional Bourne shell language.

Alternative shells are available as packages; see pkg_add(1) and chsh(1) .

Recommendation: Do not change root’s shell to a package-provided shell. Non-base shells live under /usr/local/bin, which might be unavailable in a limited-recovery scenario. The base ksh(1) resides in /bin.

# install common alternative shells (as root)
# pkg_add bash zsh

$ doas pkg_add bash zsh
$ chsh -s /usr/local/bin/zsh

Privilege escalation: doas #

OpenBSD provides doas(1) in the base system for privilege escalation. Configure it via doas.conf(5) . A documented example exists in /etc/examples/.

$ doas cp /etc/examples/doas.conf /etc/doas.conf
  # Start from the example configuration

By default, each invocation prompts for a password. To cache authentication in a manner similar to some sudo configurations, add persist:

permit persist keepenv :wheel

A sudo package is available if required; see sudo(8) .

Software management #

OpenBSD separates the base system from packages. Prefer prebuilt packages; see packages(7) . Building from ports is documented in ports(7) .

Installing and removing packages #

Install prebuilt packages with pkg_add(1) :

$ doas pkg_add nginx

Remove packages with pkg_delete(1) :

$ doas pkg_delete nginx

List installed packages with pkg_info(1) :

$ pkg_info

Updating (same release) #

OpenBSD ships binary patches for the base system via syspatch(8) .

$ doas syspatch -c
  # Show available base patches
$ doas syspatch
  # Apply base patches; reboot if required

Update installed packages to the latest for your release with:

$ doas pkg_add -Uu
  # Upgrade all packages within the current release

Upgrading (to a new release) #

Use sysupgrade(8) to fetch and perform a release upgrade. After the reboot, merge configuration changes with sysmerge(8) if prompted, then update packages.

$ doas sysupgrade
  # Upgrade base to the next release

$ doas pkg_add -Uu
  # Update packages after the base upgrade

Networking #

Interface names are driver-based on both systems, so em0, re0, and similar names are familiar. The configuration model differs.

Interface configuration with hostname.if #

Per-interface configuration lives in hostname.if(5) , where if is the interface name. For example, /etc/hostname.em0:

Static IPv4:

inet 10.0.0.100 255.255.255.0

Static IPv6:

inet6 2001:db8:6000:9344::154 64

DHCP:

dhcp

Temporary, runtime changes can be made with ifconfig(8) :

$ doas ifconfig em0 10.0.0.100 255.255.255.0

Apply configuration from files using netstart(8) :

$ doas sh /etc/netstart
  # Reload all interfaces
$ doas sh /etc/netstart em0
  # Reload a single interface

Hostname #

Set the system’s fully qualified domain name in myname(5) (/etc/myname). The name must resolve via /etc/hosts or DNS.

host.example.com

Reload networking with sh /etc/netstart after changes.

Default gateway #

Set the default gateway(s) in mygate(5) (/etc/mygate). One address per line; the first of each family is used.

192.0.2.1
2001:db8:6000:9344::1

Reload networking with sh /etc/netstart.

DNS resolvers #

Configure resolvers in resolv.conf(5) :

nameserver 192.0.2.1
lookup file bind

Reload networking with sh /etc/netstart.

Daemons and startup #

OpenBSD uses the traditional BSD init and rc system; see init(8) , rc(8) , and rc.conf(8) . System defaults are in /etc/rc.conf. Do not edit it directly; override and localize settings in /etc/rc.conf.local.

FreeBSD administrators commonly use service(8) and sysrc(8). On OpenBSD, use rcctl(8) to control and enable daemons.

To enable the base web server, httpd(8) , at boot, either use rcctl enable httpd or set an empty flags line in rc.conf.local:

httpd_flags=

Control daemons with rcctl(8) :

$ doas rcctl start httpd # Start the httpd service immediately
$ doas rcctl stop httpd # Stop the running httpd service
$ doas rcctl reload httpd # Reload httpd configuration without a full restart
$ doas rcctl enable httpd # Enable httpd to start at boot
$ doas rcctl disable httpd # Disable automatic start at boot

Common equivalents #

For further details, consult the referenced manual pages on this site.