24.2. FreeBSD Update

Written by Tom Rhodes.
Based on notes provided by Colin Percival.

Applying security patches in a timely manner and upgrading to a newer release of an operating system are important aspects of ongoing system administration. FreeBSD includes a utility called freebsd-update which can be used to perform both these tasks.

This utility supports binary security and errata updates to FreeBSD, without the need to manually compile and install the patch or a new kernel. Binary updates are available for all architectures and releases currently supported by the security team. The list of supported releases and their estimated end-of-life dates are listed at http://www.FreeBSD.org/security/.

This utility also supports operating system upgrades to minor point releases as well as upgrades to another release branch. Before upgrading to a new release, review its release announcement as it contains important information pertinent to the release. Release announcements are available from http://www.FreeBSD.org/releases/.

Note:

If a crontab utilizing the features of freebsd-update(8) exists, it must be disabled before upgrading the operating system.

This section describes the configuration file used by freebsd-update, demonstrates how to apply a security patch and how to upgrade to a minor or major operating system release, and discusses some of the considerations when upgrading the operating system.

24.2.1. The Configuration File

The default configuration file for freebsd-update works as-is. Some users may wish to tweak the default configuration in /etc/freebsd-update.conf, allowing better control of the process. The comments in this file explain the available options, but the following may require a bit more explanation:

# Components of the base system which should be kept updated.
Components world kernel

This parameter controls which parts of FreeBSD will be kept up-to-date. The default is to update the entire base system and the kernel. Individual components can instead be specified, such as src/base or src/sys. However, the best option is to leave this at the default as changing it to include specific items requires every needed item to be listed. Over time, this could have disastrous consequences as source code and binaries may become out of sync.

# Paths which start with anything matching an entry in an IgnorePaths
# statement will be ignored.
IgnorePaths /boot/kernel/linker.hints

To leave specified directories, such as /bin or /sbin, untouched during the update process, add their paths to this statement. This option may be used to prevent freebsd-update from overwriting local modifications.

# Paths which start with anything matching an entry in an UpdateIfUnmodified
# statement will only be updated if the contents of the file have not been
# modified by the user (unless changes are merged; see below).
UpdateIfUnmodified /etc/ /var/ /root/ /.cshrc /.profile

This option will only update unmodified configuration files in the specified directories. Any changes made by the user will prevent the automatic updating of these files. There is another option, KeepModifiedMetadata, which will instruct freebsd-update to save the changes during the merge.

# When upgrading to a new FreeBSD release, files which match MergeChanges
# will have any local changes merged into the version from the new release.
MergeChanges /etc/ /var/named/etc/ /boot/device.hints

List of directories with configuration files that freebsd-update should attempt to merge. The file merge process is a series of diff(1) patches similar to mergemaster(8), but with fewer options. Merges are either accepted, open an editor, or cause freebsd-update to abort. When in doubt, backup /etc and just accept the merges. See Section 24.6.4, “Merging Configuration Files” for more information about mergemaster.

# Directory in which to store downloaded updates and temporary
# files used by FreeBSD Update.
# WorkDir /var/db/freebsd-update

This directory is where all patches and temporary files are placed. In cases where the user is doing a version upgrade, this location should have at least a gigabyte of disk space available.

# When upgrading between releases, should the list of Components be
# read strictly (StrictComponents yes) or merely as a list of components
# which *might* be installed of which FreeBSD Update should figure out
# which actually are installed and upgrade those (StrictComponents no)?
# StrictComponents no

When this option is set to yes, freebsd-update will assume that the Components list is complete and will not attempt to make changes outside of the list. Effectively, freebsd-update will attempt to update every file which belongs to the Components list.

24.2.2. Applying Security Patches

The process of applying FreeBSD security patches has been simplified, allowing an administrator to keep a system fully patched using freebsd-update. More information about FreeBSD security advisories can be found in Section 14.11, “FreeBSD Security Advisories”.

FreeBSD security patches may be downloaded and installed using the following commands. The first command will determine if any outstanding patches are available, and if so, will list the files that will be modifed if the patches are applied. The second command will apply the patches.

# freebsd-update fetch
# freebsd-update install

If the update applies any kernel patches, the system will need a reboot in order to boot into the patched kernel. If the patch was applied to any running binaries, the affected applications should be restarted so that the patched version of the binary is used.

The system can be configured to automatically check for updates once every day by adding this entry to /etc/crontab:

@daily                                  root    freebsd-update cron

If patches exist, they will automatically be downloaded but will not be applied. The root user will be sent an email so that the patches may be reviewed and manually installed with freebsd-update install.

If anything goes wrong, freebsd-update has the ability to roll back the last set of changes with the following command:

# freebsd-update rollback
Uninstalling updates... done.

Again, the system should be restarted if the kernel or any kernel modules were modified and any affected binaries should be restarted.

Only the GENERIC kernel can be automatically updated by freebsd-update. If a custom kernel is installed, it will have to be rebuilt and reinstalled after freebsd-update finishes installing the updates. However, freebsd-update will detect and update the GENERIC kernel if /boot/GENERIC exists, even if it is not the current running kernel of the system.

Note:

Always keep a copy of the GENERIC kernel in /boot/GENERIC. It will be helpful in diagnosing a variety of problems and in performing version upgrades. Refer to either Section 24.2.3.1, “Custom Kernels with FreeBSD 9.X and Later” or Section 24.2.3.2, “Custom Kernels with FreeBSD 8.X” for instructions on how to get a copy of the GENERIC kernel.

Unless the default configuration in /etc/freebsd-update.conf has been changed, freebsd-update will install the updated kernel sources along with the rest of the updates. Rebuilding and reinstalling a new custom kernel can then be performed in the usual way.

The updates distributed by freebsd-update do not always involve the kernel. It is not necessary to rebuild a custom kernel if the kernel sources have not been modified by freebsd-update install. However, freebsd-update will always update /usr/src/sys/conf/newvers.sh. The current patch level, as indicated by the -p number reported by uname -r, is obtained from this file. Rebuilding a custom kernel, even if nothing else changed, allows uname to accurately report the current patch level of the system. This is particularly helpful when maintaining multiple systems, as it allows for a quick assessment of the updates installed in each one.

24.2.3. Performing Major and Minor Version Upgrades

Upgrades from one minor version of FreeBSD to another, like from FreeBSD 9.0 to FreeBSD 9.1, are called minor version upgrades. Major version upgrades occur when FreeBSD is upgraded from one major version to another, like from FreeBSD 9.X to FreeBSD 10.X. Both types of upgrades can be performed by providing freebsd-update with a release version target.

Note:

If the system is running a custom kernel, make sure that a copy of the GENERIC kernel exists in /boot/GENERIC before starting the upgrade. Refer to either Section 24.2.3.1, “Custom Kernels with FreeBSD 9.X and Later” or Section 24.2.3.2, “Custom Kernels with FreeBSD 8.X” for instructions on how to get a copy of the GENERIC kernel.

The following command, when run on a FreeBSD 9.0 system, will upgrade it to FreeBSD 9.1:

# freebsd-update -r 9.1-RELEASE upgrade

After the command has been received, freebsd-update will evaluate the configuration file and current system in an attempt to gather the information necessary to perform the upgrade. A screen listing will display which components have and have not been detected. For example:

Looking up update.FreeBSD.org mirrors... 1 mirrors found.
Fetching metadata signature for 9.0-RELEASE from update1.FreeBSD.org... done.
Fetching metadata index... done.
Inspecting system... done.

The following components of FreeBSD seem to be installed:
kernel/smp src/base src/bin src/contrib src/crypto src/etc src/games
src/gnu src/include src/krb5 src/lib src/libexec src/release src/rescue
src/sbin src/secure src/share src/sys src/tools src/ubin src/usbin
world/base world/info world/lib32 world/manpages

The following components of FreeBSD do not seem to be installed:
kernel/generic world/catpages world/dict world/doc world/games
world/proflibs

Does this look reasonable (y/n)? y

At this point, freebsd-update will attempt to download all files required for the upgrade. In some cases, the user may be prompted with questions regarding what to install or how to proceed.

When using a custom kernel, the above step will produce a warning similar to the following:

WARNING: This system is running a "MYKERNEL" kernel, which is not a
kernel configuration distributed as part of FreeBSD 9.0-RELEASE.
This kernel will not be updated: you MUST update the kernel manually
before running "/usr/sbin/freebsd-update install"

This warning may be safely ignored at this point. The updated GENERIC kernel will be used as an intermediate step in the upgrade process.

Once all the patches have been downloaded to the local system, they will be applied. This process may take a while, depending on the speed and workload of the machine. Configuration files will then be merged. The merging process requires some user intervention as a file may be merged or an editor may appear on screen for a manual merge. The results of every successful merge will be shown to the user as the process continues. A failed or ignored merge will cause the process to abort. Users may wish to make a backup of /etc and manually merge important files, such as master.passwd or group at a later time.

Note:

The system is not being altered yet as all patching and merging is happening in another directory. Once all patches have been applied successfully, all configuration files have been merged and it seems the process will go smoothly, the changes can be committed to disk by the user using the following command:

# freebsd-update install

The kernel and kernel modules will be patched first. If the system is running with a custom kernel, use nextboot(8) to set the kernel for the next boot to the updated /boot/GENERIC:

# nextboot -k GENERIC

Warning:

Before rebooting with the GENERIC kernel, make sure it contains all the drivers required for the system to boot properly and connect to the network, if the machine being updated is accessed remotely. In particular, if the running custom kernel contains built-in functionality usually provided by kernel modules, make sure to temporarily load these modules into the GENERIC kernel using the /boot/loader.conf facility. It is recommended to disable non-essential services as well as any disk and network mounts until the upgrade process is complete.

The machine should now be restarted with the updated kernel:

# shutdown -r now

Once the system has come back online, restart freebsd-update using the following command. Since the state of the process has been saved, freebsd-update will not start from the beginning, but will instead move on to the next phase and remove all old shared libraries and object files.

# freebsd-update install

Note:

Depending upon whether any library version numbers were bumped, there may only be two install phases instead of three.

The upgrade is now complete. If this was a major version upgrade, reinstall all ports and packages as described in Section 24.2.3.3, “Rebuilding Ports After a Major Version Upgrade”.

24.2.3.1. Custom Kernels with FreeBSD 9.X and Later

Before using freebsd-update, ensure that a copy of the GENERIC kernel exists in /boot/GENERIC. If a custom kernel has only been built once, the kernel in /boot/kernel.old is the GENERIC kernel. Simply rename this directory to /boot/kernel.

If a custom kernel has been built more than once or if it is unknown how many times the custom kernel has been built, obtain a copy of the GENERIC kernel that matches the current version of the operating system. If physical access to the system is available, a copy of the GENERIC kernel can be installed from the installation media:

# mount /cdrom
# cd /cdrom/usr/freebsd-dist
# tar -C/ -xvf kernel.txz boot/kernel/kernel

Alternately, the GENERIC kernel may be rebuilt and installed from source:

# cd /usr/src
# make kernel __MAKE_CONF=/dev/null SRCCONF=/dev/null

For this kernel to be identified as the GENERIC kernel by freebsd-update, the GENERIC configuration file must not have been modified in any way. It is also suggested that the kernel is built without any other special options.

Rebooting into the GENERIC kernel is not required as freebsd-update only needs /boot/GENERIC to exist.

24.2.3.2. Custom Kernels with FreeBSD 8.X

On an FreeBSD 8.X system, the instructions for obtaining or building a GENERIC kernel differ slightly.

Assuming physical access to the machine is possible, a copy of the GENERIC kernel can be installed from the installation media using the following commands:

# mount /cdrom
# cd /cdrom/X.Y-RELEASE/kernels
# ./install.sh GENERIC

Replace X.Y-RELEASE with the version of the release being used. The GENERIC kernel will be installed in /boot/GENERIC by default.

To instead build the GENERIC kernel from source:

# cd /usr/src
# env DESTDIR=/boot/GENERIC make kernel __MAKE_CONF=/dev/null SRCCONF=/dev/null
# mv /boot/GENERIC/boot/kernel/* /boot/GENERIC
# rm -rf /boot/GENERIC/boot

For this kernel to be picked up as GENERIC by freebsd-update, the GENERIC configuration file must not have been modified in any way. It is also suggested that it is built without any other special options.

Rebooting into the GENERIC kernel is not required.

24.2.3.3. Rebuilding Ports After a Major Version Upgrade

Generally, installed applications will continue to work without problems after minor version upgrades. Major versions use different Application Binary Interfaces (ABIs), which will break most third-party applications. After a major version upgrade, all installed packages and ports need to be upgraded using a utility such as ports-mgmt/portmaster. A rebuild of all installed applications can be accomplished with this command:

# portmaster -af

This command will display the configuration screens for each application that has configurable options and wait for the user to interact with those screens. To prevent this behavior, and use only the default options, include -G in the above command.

Once the software upgrades are complete, finish the upgrade process with a final call to freebsd-update in order to tie up all the loose ends in the upgrade process:

# freebsd-update install

If the GENERIC kernel was temporarily used, this is the time to build and install a new custom kernel using the instructions in Chapter 9, Configuring the FreeBSD Kernel.

Reboot the machine into the new FreeBSD version. The upgrade process is now complete.

24.2.4. System State Comparison

The state of the installed FreeBSD version against a known good copy can be tested using freebsd-update IDS. This command evaluates the current version of system utilities, libraries, and configuration files and can be used as a built-in Intrusion Detection System (IDS).

Warning:

This command is not a replacement for a real IDS such as security/snort. As freebsd-update stores data on disk, the possibility of tampering is evident. While this possibility may be reduced using kern.securelevel and by storing the freebsd-update data on a read-only file system when not in use, a better solution would be to compare the system against a secure disk, such as a DVD or securely stored external USB disk device. An alternative method for providing IDS functionality using a built-in utility is described in Section 14.2.6, “Binary Verification”

To begin the comparison, specify the output file to save the results to:

# freebsd-update IDS >> outfile.ids

The system will now be inspected and a lengthy listing of files, along with the SHA256 hash values for both the known value in the release and the current installation, will be sent to the specified output file.

The entries in the listing are extremely long, but the output format may be easily parsed. For instance, to obtain a list of all files which differ from those in the release, issue the following command:

# cat outfile.ids | awk '{ print $1 }' | more
/etc/master.passwd
/etc/motd
/etc/passwd
/etc/pf.conf

This sample output has been truncated as many more files exist. Some files have natural modifications. For example, /etc/passwd will be modified if users have been added to the system. Kernel modules may differ as freebsd-update may have updated them. To exclude specific files or directories, add them to the IDSIgnorePaths option in /etc/freebsd-update.conf.

All FreeBSD documents are available for download at http://ftp.FreeBSD.org/pub/FreeBSD/doc/

Questions that are not answered by the documentation may be sent to <freebsd-questions@FreeBSD.org>.
Send questions about this document to <freebsd-doc@FreeBSD.org>.