OpenBSD for Linux Users

This quickstart introduces Linux 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 is already installed and you have command-line access. For installation, see the site’s installation chapter.

Shells #

The default shell for both root and regular users is the Korn shell, ksh(1) . Its command language is a superset of the traditional Bourne shell. Shells such as Bash and Zsh 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 may be unavailable in a limited-recovery scenario. The base ksh(1) resides in /bin.

# install common alternative shells (as root)
# use doas(1) from a regular account; see the next section
# pkg_add bash zsh

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

Privilege escalation: doas (instead of sudo) #

OpenBSD provides doas(1) for privilege escalation. Configure it via doas.conf(5) . A sample file exists in /etc/examples/.

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

By default, each invocation prompts for a password. To cache authentication similarly to many sudo setups, use the persist option:

permit persist keepenv :wheel

A sudo package is available if required; see sudo(8) . In most workflows, doas fulfills the same role with simpler configuration.

Software management #

OpenBSD separates the base system from packages. Package tools are documented in packages(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) . Use it regularly:

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

Packages are updated independently within a release. To update installed packages to the latest for your release, use:

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

Upgrading (to a new release) #

OpenBSD targets approximately two releases per year. Use sysupgrade(8) to fetch and perform a release upgrade:

$ doas sysupgrade

After the base upgrade and reboot, update packages:

$ doas pkg_add -Uu

Networking #

OpenBSD names network interfaces by driver name rather than eth0, enp0s1, and so on. Examples include re0 (Realtek), bge0 (Broadcom), and em0 (Intel). See ifconfig(8) for details.

Interface configuration with hostname.if #

Per-interface configuration lives in hostname.if(5) , where if is the interface name. For example, /etc/hostname.re0:

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 re0 10.0.0.100 255.255.255.0

Apply configuration from files using the same script used at boot, netstart(8) :

$ doas sh /etc/netstart
  # Reload all interfaces
$ doas sh /etc/netstart re0
  # 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) . There are no SysV-style run levels.

System defaults are in /etc/rc.conf. Do not edit it directly; override and localize settings in /etc/rc.conf.local.

To enable the base web server, httpd(8) , at boot, either use rcctl(8) 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 command equivalents #

See pkg_add(1) , pkg_info(1) , pcidump(8) , and usbdevs(8) for details.