OpenBSD FAQ - Migrating to OpenBSD [FAQ Index]



Tips for users of other Unix-like operating systems

While OpenBSD is a very traditional Unix-like operating system and will be very familiar to those who have used other Unix-like systems, there are important differences. New users to OpenBSD must look at their own experience: if your only knowledge of Unix is some experience with one variant of Linux, you may find OpenBSD "strange." Rest assured, Linux looks pretty strange to anyone who starts from OpenBSD. You must recognize the difference between "standard" and your experience.

If you learned Unix from any of the good books on general Unix, understanding the "Unix philosophy" and then extending your knowledge to a particular platform, you will find OpenBSD to be a very "true" and familiar Unix. If you learned Unix using a "type this to do that" process or a book such as "Learn PinkBeenie v8.3 in 31.4 Hours" and told yourself you "know" Unix, you will most likely find OpenBSD very different.

One important difference between OpenBSD and many other operating systems is the documentation. OpenBSD developers take great pride in the system man pages. The man pages are the authoritative source of OpenBSD documentation -- not this FAQ, not third-party independently maintained pages, not "howto" guides, etc. When a developer makes a change to the system, they are expected to update the man pages along with their change to the system code, not "later" or "when they get around to it" or "when someone complains." A manual page exists for virtually every program, utility, driver, configuration file, and so on on the stock system. It is expected that a user will check the man pages before asking for help on the mailing lists.

Here are some of the commonly encountered differences between OpenBSD and other Unix variants.

Dual booting Linux and OpenBSD (amd64/i386)

Multibooting is not trivial, and it requires an understanding of ALL the operating systems you wish to have coexist on the machine. The GRUB loader commonly used with Linux can boot OpenBSD as a generic operating system. From time to time, GRUB tries to natively handle OpenBSD booting -- using this feature is NOT recommended, as there is no coordination with OpenBSD development. As such, this feature is often broken, and there's really no need for it. Just use OpenBSD's boot code, and what GRUB terms "chain loading" to invoke it.

A GRUB entry which could boot OpenBSD installed on the second MBR partition (partition "1" in OpenBSD's fdisk) might look like:

menuentry "OpenBSD" {
	set root=(hd0,2)
	chainloader +1
}
Your milage will vary.

Converting your Linux (or other Sixth Edition-style) password file to BSD-style

First, figure out if your Linux password file is shadowed or not. If it is, install John the Ripper from packages or ports (security/john) and use the "unshadow" utility that comes with it to merge your passwd and shadow files into one Sixth Edition-style file.

Using your Linux password file, we'll call it linux_passwd, you need to add in ::0:0 between fields four and seven. awk(1) does this for you.

# awk -F : '{printf("%s:%s:%s:%s::0:0:%s:%s:%s\n", \
> $1,$2,$3,$4,$5,$6,$7); }' linux_passwd > new_passwd
At this point, you want to edit the new_passwd file and remove the root and other system entries that are already present in your OpenBSD password file or aren't applicable with OpenBSD (all of them). Also, make sure there are no duplicate usernames or user IDs between new_passwd and your OpenBSD box's /etc/passwd. The easiest way to do this is to start with a fresh /etc/passwd.
# cat new_passwd >> /etc/master.passwd
# pwd_mkdb -p /etc/master.passwd
The last step, pwd_mkdb is necessary to rebuild the /etc/spwd.db and /etc/pwd.db files. It also creates a Sixth Edition-style password file (minus encrypted passwords) at /etc/passwd for programs which use it. OpenBSD uses a stronger encryption for passwords, blowfish, which is very unlikely to be found on any system which uses full Sixth Edition-style password files. To switch over to this stronger encryption, simply have the users run passwd and change their password. The new password they enter will be encrypted with your default setting (usually blowfish unless you've edited /etc/login.conf). Or, as root, you can run passwd username.

Accessing your Linux files from OpenBSD

OpenBSD supports the EXT2 file system for read/write, and can read EXT4. See also here.