Copyright © 2008 The FreeBSD Documentation Project
FreeBSD is a registered trademark of the FreeBSD Foundation.
Linux is a registered trademark of Linus Torvalds.
Intel, Celeron, EtherExpress, i386, i486, Itanium, Pentium, and Xeon are trademarks or registered trademarks of Intel Corporation or its subsidiaries in the United States and other countries.
Red Hat, RPM, are trademarks or registered trademarks of Red Hat, Inc. in the United States and other countries.
UNIX is a registered trademark of The Open Group in the United States and other countries.
Many of the designations used by manufacturers and sellers to distinguish their products are claimed as trademarks. Where those designations appear in this document, and the FreeBSD Project was aware of the trademark claim, the designations have been followed by the “™” or the “®” symbol.
This document is intended to quickly familiarize intermediate to advanced Linux® users with the basics of FreeBSD.
This document will highlight the differences between FreeBSD and Linux® so that intermediate to advanced Linux® users can quickly familiarize themselves with the basics of FreeBSD. This is just a technical quickstart, it does not attempt to design “philosophical” differences between the two operating systems.
This document assumes that you have already installed FreeBSD. If you have not installed FreeBSD or need help with the installation process please refer to the Installing FreeBSD chapter of the FreeBSD Handbook.
Those coming from Linux® are often surprised to find that Bash is not the default shell in FreeBSD. In fact, Bash is not even in the default installation. Instead, FreeBSD uses tcsh(1) as the default shell. Although, Bash and your other favorite shells are available in FreeBSD's Packages and Ports Collection.
If you do install other shells you can use chsh(1) to set
a user's default shell. It is, however, recommended that the
root's default shell remain unchanged. The
reason for this is that shells not included in the base distribution
are normally installed in /usr/local/bin or
/usr/bin. In the event of a problem the file
systems where /usr/local/bin and
/usr/bin are located may not be mounted. In this
case root would not have access to its default
shell, preventing root from logging in. For this
reason a second root account, the
toor account, was created for use with non-default
shells. See the security FAQ for information regarding the toor account.
In addition to the traditional UNIX® method of installing software (download source, extract, edit source code, and compile), FreeBSD offers two other methods for installing applications: packages and ports. A complete list of of all available ports and packages can be found here.
Packages are pre-compiled applications, the FreeBSD equivalents
of .deb files on Debian/Ubuntu based systems
and .rpm files on Red Hat/Fedora based
systems. Packages are installed using pkg_add(1). For example,
the following command installs
Apache 2.2:
#pkg_add /tmp/apache-2.2.6_2.tbz
Using the -r switch will tell pkg_add(1)
to automatically fetch a package and install it, as well as any
dependencies:
#pkg_add -r apache22Fetching ftp://ftp.freebsd.org/pub/FreeBSD/ports/i386/packages-6.2-release/Latest/apache22.tbz... Done. Fetching ftp://ftp.freebsd.org/pub/FreeBSD/ports/i386/packages-6.2-release/All/expat-2.0.0_1.tbz... Done. Fetching ftp://ftp.freebsd.org/pub/FreeBSD/ports/i386/packages-6.2-release/All/perl-5.8.8_1.tbz... Done. [snip] To run apache www server from startup, add apache22_enable="YES" in your /etc/rc.conf. Extra options can be found in startup script.
If you are running a release version of FreeBSD (6.2, 6.3, 7.0,
etc., generally installed from CD-ROM) pkg_add -r
will download packages built for that specific release. These
packages may not be the most up-to-date
version of the application. You can use the
PACKAGESITE variable to override this default
behavior. For example, set PACKAGESITE to
ftp://ftp.freebsd.org/pub/FreeBSD/ports/i386/packages-6-stable/Latest/
to download the most recent packages built for the
6.X series.
For more information on packages please refer to section 4.4 of the FreeBSD Handbook: Using the Packages System.
FreeBSD's second method for installing applications is the
Ports Collection. The Ports Collection is a framework of
Makefiles and patches specifically customized
for installing various software applications from source on FreeBSD.
When installing a port the system will fetch the source code, apply
any required patches, compile the code, and install the application
(and do the same for any dependencies).
The Ports Collection, sometimes referred to as the ports tree,
can be found in /usr/ports. That is assuming
the Ports Collection was installed during the FreeBSD installation
process. If the Ports Collection has not been installed it can be
added from the installation discs using sysinstall(8), or pulled
from the FreeBSD servers using csup(1) or portsnap(8).
Detailed instructions for installing the Ports Collection can be
found in section 4.5.1
of the handbook.
Installing a port is as simple (generally) as changing in to the port's directory and starting the build process. The following example installs Apache 2.2 from the Ports Collection:
#cd /usr/ports/www/apache22#make install clean
A major benefit of using ports to install software is the
ability to customize the installation options. For example, when
installing Apache 2.2 from ports you can
enable mod_ldap by setting the
WITH_LDAP make(1) variable:
#cd /usr/ports/www/apache22#make WITH_LDAP="YES" install clean
Please see section 4.5 of the FreeBSD Handbook, Using the Ports Collection, for more information about the Ports Collection.
Packages are just pre-compiled ports, so it is really a matter of installing from source (ports) versus installing from binary packages. Each method has its own benefits:
If you do not have any special requirements, packages will
probably suit your situation just fine. If you may ever need to
customize, ports are the way to go. (And remember, if you
need to customize but prefer packages, you can build a custom
package from ports using make
package and then copy the package to
other servers.)
Linux® uses the SysV init system, whereas FreeBSD uses the
traditional BSD-style init(8). Under the BSD-style init(8)
there are no run-levels and no /etc/inittab,
instead startup is controlled by the rc(8) utility. The
/etc/rc script reads
/etc/defaults/rc.conf and
/etc/rc.conf to determine which services are to be
started. The specified services are then started by running the
corresponding service initialization scripts located in
/etc/rc.d/ and
/usr/local/etc/rc.d/. These scripts are similar to
the scripts located in /etc/init.d/ on Linux®
systems.
Services are enabled by specifying
ServiceName_enable="YES" in
/etc/rc.conf (rc.conf(5)). Take a look at
/etc/defaults/rc.conf for the system defaults,
these default settings are overridden by settings in
/etc/rc.conf. Also, when installing additional
applications be sure to review the documentation to determine how to
enable any associated services.
The following snippet from /etc/rc.conf enables
sshd(8) and Apache 2.2. It also
specifies that Apache should be started
with SSL.
# enable SSHD sshd_enable="YES" # enable Apache with SSL apache22_enable="YES" apache22_flags="-DSSL"
Once a service has been enabled in /etc/rc.conf,
the service can be started from the command line (without rebooting the
system):
#/etc/rc.d/sshd start
If a service has not been enabled it can be started from the
command line using forcestart:
#/etc/rc.d/sshd forcestart
Instead of a generic ethX identifier that
Linux® uses to identify a network interface, FreeBSD uses the driver
name followed by a number as the identifier. The following output
from ifconfig(8) shows two Intel® Pro 1000 network
interfaces (em0 and em1):
%ifconfigem0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500 options=b<RXCSUM,TXCSUM,VLAN_MTU> inet 10.10.10.100 netmask 0xffffff00 broadcast 10.10.10.255 ether 00:50:56:a7:70:b2 media: Ethernet autoselect (1000baseTX <full-duplex>) status: active em1: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500 options=b<RXCSUM,TXCSUM,VLAN_MTU> inet 192.168.10.222 netmask 0xffffff00 broadcast 192.168.10.255 ether 00:50:56:a7:03:2b media: Ethernet autoselect (1000baseTX <full-duplex>) status: active
An IP address can be assigned to an interface using
ifconfig(8). However, to remain persistent across reboots the
IP configuration must be included in
/etc/rc.conf. The following example
specifies the hostname, IP address, and default gateway:
hostname="server1.example.com" ifconfig_em0="inet 10.10.10.100 netmask 255.255.255.0" defaultrouter="10.10.10.1"
Use the following to configure an interface for DHCP:
hostname="server1.example.com" ifconfig_em0="DHCP"
Like IPTABLES in Linux®, FreeBSD also offers a kernel level firewall; actually FreeBSD offers three firewalls:
IPFIREWALL or IPFW (the command to manage an IPFW ruleset is ipfw(8)) is the firewall developed and maintained by the FreeBSD developers. IPFW can be paired with dummynet(4) to provide traffic shaping capabilities and simulate different types of network connections.
Sample IPFW rule to allow SSH in:
ipfw add allow tcp from any to me 22 in via $ext_if
IPFILTER is the firewall application developed by Darren Reed. It is not specific to FreeBSD, and has been ported to several operating systems including NetBSD, OpenBSD, SunOS, HP/UX, and Solaris.
Sample IPFILTER command to allow SSH in:
pass in on $ext_if proto tcp from any to any port = 22
The last firewall application, PF, is developed by the OpenBSD project. PF was created as a replacement for IPFILTER. As such, the PF syntax is very similar to that of IPFILTER. PF can be paired with altq(4) to provide QoS features.
Sample PF command to allow SSH in:
pass in on $ext_if inet proto tcp from any to ($ext_if) port 22
There are three methods for updating a FreeBSD system: from source, binary updates, and the installation discs.
Updating from source is the most involved update method, but offers the greatest amount of flexibility. The process involves synchronizing a local copy of the FreeBSD source code with the FreeBSD Subversion servers. Once the local source code is up to date you can build new versions of the kernel and userland. For more information on source updates see the chapter on updating in the FreeBSD Handbook.
Binary updates are similar to using yum or
apt-get to update a Linux® system. The command
freebsd-update(8) will fetch new updates and install them. The
updates can be scheduled using cron(8).
If you do use cron(8) to schedule the updates, please be sure
to use freebsd-update cron in your crontab(1)
to reduce the possibility of a large number of machines all pulling
updates at the same time.
0 3 * * * root /usr/sbin/freebsd-update cron
The last update method, updating from the installation discs, is a straight-forward process. Boot from the installation discs and select the option to upgrade.
In Linux®, you may have looked at
/proc/sys/net/ipv4/ip_forward to determine if
IP forwarding was enabled. Under FreeBSD you should use sysctl(8) to
view this and other system settings, as procfs(5) has been
deprecated in current versions of FreeBSD. (Although
sysctl is available in Linux® as well.)
In the IP forwarding example, you would use the following to determine if IP forwarding is enabled on your FreeBSD system:
%sysctl net.inet.ip.forwardingnet.inet.ip.forwarding: 0
The -a flag is used to list all the system
settings:
%sysctl -akern.ostype: FreeBSD kern.osrelease: 6.2-RELEASE-p9 kern.osrevision: 199506 kern.version: FreeBSD 6.2-RELEASE-p9 #0: Thu Nov 29 04:07:33 UTC 2007 root@i386-builder.daemonology.net:/usr/obj/usr/src/sys/GENERIC kern.maxvnodes: 17517 kern.maxproc: 1988 kern.maxfiles: 3976 kern.argmax: 262144 kern.securelevel: -1 kern.hostname: server1 kern.hostid: 0 kern.clockrate: { hz = 1000, tick = 1000, profhz = 666, stathz = 133 } kern.posix1version: 200112 ...
Some of these sysctl values are
read-only.
There are occasions where procfs is required, such as running
older software, using truss(1) to trace system calls, and
Linux® Binary Compatibility.
(Although, Linux® Binary Compatibility uses its own procfs, linprocfs(5).)
If you need to mount procfs you can add the following to
/etc/fstab:
proc /proc procfs rw,noauto 0 0
noauto will prevent
/proc from being automatically mounted at
boot.
And then mount procfs with:
#mount /proc
| Linux® command (Red Hat/Debian) | FreeBSD equivalent | Purpose |
|---|---|---|
yum install package / apt-get install package | pkg_add -r package | Install package from remote repository |
rpm -ivh package / dpkg -i package | pkg_add -v package | Install package |
rpm -qa / dpkg -l | pkg_info | List installed packages |
Hopefully this document has provided you with enough to get started with FreeBSD. Be sure to take a look at the FreeBSD Handbook for more in depth coverage of the topics touched on as well as the many topics not covered in this document.