OpenBSD
FAQ - Building the System from Source
[FAQ Index]
OpenBSD's Flavors
There are three flavors of OpenBSD:
- releases: The version of OpenBSD shipped every six months.
- -current: The development branch.
Every six months, -current is tagged and becomes the next release.
- -stable: A release plus patches found on the
errata page.
When very important fixes are made to -current, they are backported
to the supported -stable branches.
Only the two most recent OpenBSD releases receive
security and reliability fixes for the
base system.
New users should be running either -stable or a release.
That being said, many people do run -current on production systems to
help catch bugs and test new features.
Development Snapshots
Snapshots of the -current branch are made available between formal releases
of OpenBSD.
These are builds of whatever code is in the tree at the time.
A recent snapshot is usually all you need to run -current.
If you wish to build it from source, starting from the latest snapshot is
required.
Check the following -current and using snapshots
page for any configuration changes or extra steps needed to build from source.
It is possible that you may uncover bugs in snapshots.
This is one of the reasons why they are built and distributed.
If you find a bug, make sure it is reported.
Building OpenBSD from Source
Building OpenBSD from source involves a number of steps:
- Upgrading to the closest available binaries
- Fetching the source code
- Building a new kernel and userland, as explained in steps 2 and 3 of
release(8)
- Optionally, making a release and
building X
This FAQ section is intended to help you with the necessary preparation.
The main reference is release(8).
Upgrading to the Closest Available Binaries
Do not attempt to go from one release to another by compiling from source.
Make sure you have the closest available binaries installed.
This is either OpenBSD x.y if you want to build OpenBSD x.y-stable,
or the latest snapshot if you wish to build -current.
Fetching the Source Code
OpenBSD uses the CVS
version control system to manage its source.
The cvs(1) program is used to pull a
copy of the desired source to your local machine for compilation.
An introduction to cvs(1)
and detailed instructions for fetching the source trees are on the
anonymous CVS page.
First, you must cvs checkout the source tree.
After that, you maintain the tree by running cvs update to pull
updated files to your local tree.
You can also maintain a local CVS repository using the reposync
program, available as a package.
Setting up a mirror of the repository is also explained on the
anonymous CVS page.
Avoiding Root Privileges
Avoid running cvs(1) as root.
The /usr/src directory (where your source will typically go) is
writable by the wsrc group by default, so add users that need
to use cvs(1) to that group.
# user mod -G wsrc exampleuser
This change takes effect with exampleuser's next login.
If you want to fetch xenocara or ports as this user, you must create the
directories and set their permissions manually.
# cd /usr
# mkdir -p xenocara ports
# chgrp wsrc xenocara ports
# chmod 775 xenocara ports
Fetching -stable
To fetch the -stable src tree, specify the branch you want with
the -r flag:
$ cd /usr
$ cvs -qd anoncvs@anoncvs.example.org:/cvs checkout -rOPENBSD_7_7 -P src
Once you have the tree checked out, you can update it at a later time with:
$ cd /usr/src
$ cvs -q up -Pd -rOPENBSD_7_7
Replace src with xenocara or ports
as appropriate.
As all parts of OpenBSD must be kept in sync, all the trees you use should be
checked out and updated at the same time.
Fetching -current
To fetch a -current src tree, you can use the following:
$ cd /usr
$ cvs -qd anoncvs@anoncvs.example.org:/cvs checkout -P src
Update the tree with:
$ cd /usr/src
$ cvs -q up -Pd -A
Replace src with the module you want, such as xenocara
or ports.
Building OpenBSD
At this point you are ready to build OpenBSD from source.
If you are building -current, review changes and special build
instructions listed on this page.
Follow the detailed instructions in steps 2 and 3 of
release(8).
Further Reading on the Build Process
- mk.conf(5)
-
src/Makefile
-
/usr/share/mk/bsd.README
- config(8)
- options(4)
Making a Release
A release is the complete set of files that can be used to install or upgrade
OpenBSD on another system.
An example use would be to build -stable on a fast machine, then make a
release to be installed on all your other machines.
If you have only one computer running OpenBSD, you really don't have any reason
to make a release, as the above build process will do everything you need.
The instructions on making a release are in
release(8).
The release process uses the binaries created in the /usr/obj
directory in the building process above.
Note: if you wish to distribute the resulting file sets by HTTP(s) for use by
the upgrade or install scripts, you will need to add an index.txt
file that contains the list of all the files in your newly created release.
# ls -nT > index.txt
If you'd like to cryptographically sign the sets you created, the
signify(1) man page has details
on how to do so.
Setting Up Your System
Making a release requires a noperm partition.
This allows the build infrastructure to use the unprivileged build
user for much of the process.
Create a filesystem on /dest with the noperm
mount(8) option set.
The corresponding fstab(5)
line might look like this:
c73d2198f83ef845.m /dest ffs rw,nosuid,noperm 1 2
The root directory of this filesystem must be owned by build with
permissions 700:
# chown build /dest
# chmod 700 /dest
Create the DESTDIR directories for base and xenocara:
# mkdir /dest/{,x}base
Your RELEASEDIR does not need to be on a noperm
filesystem.
Make sure that it is owned by build and has at least permissions
u=rwx.
Using an mfs noperm Partition
You may want to use an mfs
partition instead of a physical disk.
Add a line similar to this to your /etc/fstab:
swap /dest mfs rw,nosuid,noperm,-P/var/dest,-s1.5G,noauto 0 0
Create the prototype DESTDIR directories:
# mkdir -p /var/dest/{,x}base
# chown -R build /var/dest
# chmod -R 700 /var/dest
Now you can mount /dest before making a release:
# mount /dest
Building X
Starting with X.Org v7, X switched to a
modular build system, splitting the X.Org source tree into more than
three hundred more-or-less independent packages.
To simplify life for OpenBSD users, a meta-build called
Xenocara was developed.
This system converts X back into one big tree to be built in one process.
As an added bonus, this build process is much more similar to the build
process used by the rest of OpenBSD than the previous versions were.
The official instructions for building X exist in the
xenocara/README.md file and in step 5 of
release(8).
Common Problems When Compiling
Most of the time, problems in the build process are caused by not following the
directions carefully.
There are occasional real problems with building -current from the most
recent snapshot, but failures when building a release or -stable
are almost always user error.
Most problems are usually one of the following:
I forgot to make obj before make build
By doing a make build before doing a make obj,
you will end up with the object files scattered in your /usr/src
directory.
This is a bad thing.
If you wish to try to avoid re-fetching your entire src tree again, you
can try the following to clean out obj files:
$ cd /usr/src
$ find . -type l -name obj -delete
$ make cleandir
$ rm -rf /usr/obj/*
$ make obj
The build stopped with a "Signal 11" error
Building OpenBSD and other programs from source is a task which pushes hardware
harder than most others, making intensive use of CPU, disk and memory.
Signal 11 failures are typically caused by hardware problems.
You will probably find it best to repair or replace the components that are
causing trouble, as problems may show themselves in other ways in the future.
For much more information, see the
Sig11 FAQ.
Miscellaneous Questions and Tips
Add your user to the wobj group
If you intend to compile individual programs in the source tree -- for example,
to do development -- you'll want to add your user to the wobj
group.
This will allow you to write to /usr/obj.
Tag Files
Being editors for developers, mg(1)
and vi(1) have built-in support for
ctags(1) files, which allow you
to navigate source trees quickly.
In most program or library source directories, you can create a
./tags
file by running:
$ make tags
When building and installing libc, a
/var/db/libc.tags file is also created.
By default, kernel tags for each architecture are located in
/sys/arch/$(machine)/.
These files can be created with make tags from
/sys/kern.
You may want to run make links as root to place a symlink to
your architecture's kernel tags file in each directory and in
/var/db/.
How do I skip building parts of the tree?
Use the SKIPDIR option of
mk.conf(5).
Can I cross-compile?
Cross-compiling tools are in the system, for use by developers bringing
up a new platform.
However, they are not maintained for general use.
When the developers bring up support for a new platform, one of the
first big tests is a native-build.
Building the system from source puts considerable load on the OS and machine,
and does a very good job of testing how well the system really works.
For this reason, OpenBSD does all the build process on the platform the build
is being used for.
Custom Kernels
There are three ways to customize a kernel:
- temporary boot-time configuration using
boot_config(8)
- permanent modification of a compiled kernel using
config(8)
- compilation of a custom kernel
Boot-Time Configuration
OpenBSD's boot-time kernel configuration,
boot_config(8),
allows an administrator to modify certain kernel settings, such as
enabling or disabling support for various devices, without recompiling
the kernel itself.
To boot into the User Kernel Config, or UKC, use the -c
option at startup time:
Using drive 0, partition 3.
Loading......
probing: pc0 com0 com1 mem[638K 1918M a20=on]
disk: hd0+ hd1+
>> OpenBSD/amd64 BOOT 3.33
boot> boot hd0a:/bsd -c
Doing this will bring up a UKC prompt.
Type help for a list of available commands.
Using boot_config(8)
only provides a temporary change, meaning the procedure would have to be
repeated on every reboot.
The next section explains how to make the changes permanent.
Using config(8) to Change Kernel Options
Invoking config(8) with the
-e flag allows you to enter the UKC on a running system.
Any changes made will then take effect on the next reboot.
The -u flag tests to see if any changes were made to the running
kernel during boot, meaning you used boot -c to enter the UKC
while booting the system.
To avoid the risk of overwriting the working kernel with a broken one,
consider using the -o flag to write the changes out to a
separate kernel file for testing:
# config -e -o /bsd.new /bsd
This will write your changes to the /bsd.new file.
Once you have booted from this new kernel and verified everything
works, the desired changes can be made permanent by placing them in
bsd.re-config(5).
Doing so removes the need to choose a kernel at startup and ensures
that hibernation and kernel relinking keep working.
Kernel modification examples are given in the
config(8) man page.
Building a Custom Kernel
Only the GENERIC and GENERIC.MP kernels are supported
by the OpenBSD team.
The GENERIC kernel configuration is the combination of the options
in /sys/arch/$(machine)/conf/GENERIC
and /sys/conf/GENERIC.
Reporting a problem on a customized kernel will almost always result in
you being told to try to reproduce the problem with a GENERIC
kernel.
Read the config(8) and the
options(4) man pages first.
The following steps are part of compiling a custom kernel:
$ cd /sys/arch/$(machine)/conf
$ cp GENERIC CUSTOM
$ vi CUSTOM # make your changes
$ config CUSTOM
$ cd ../compile/CUSTOM
$ make
Preparing a Diff
If you have made changes to the source code that you want to share
with developers, follow these conventions:
- Base your diff on a -current checkout.
- Use
cvs diff -uNp to generate the diff.
- Send your diff inline in an email to the tech
mailing list.
Make sure your email client does not mangle the whitespace.
If you are using a git mirror
of the OpenBSD source tree, set
$ git config diff.noprefix true
$ git config diff.renames false
in your repository and generate your diff like this:
$ git diff --relative .
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