FreeBSD is a modern operating system for desktops, laptops, servers, and embedded systems with support for a large number of platforms.

It is based on U.C. Berkeley's “4.4BSD-Lite” release, with some “4.4BSD-Lite2” enhancements. It is also based indirectly on William Jolitz's port of U.C. Berkeley's “Net/2” to the i386™, known as “386BSD”, though very little of the 386BSD code remains.

FreeBSD is used by companies, Internet Service Providers, researchers, computer professionals, students and home users all over the world in their work, education and recreation.

For more detailed information on FreeBSD, refer to the FreeBSD Handbook.

The goal of the FreeBSD Project is to provide a stable and fast general purpose operating system that may be used for any purpose without strings attached.

Yes. Those restrictions do not control how the code is used, but how to treat the FreeBSD Project itself. The license itself is available at license and can be summarized like this:

Many of us have a significant investment in the project and would certainly not mind a little financial compensation now and then, but we definitely do not insist on it. We believe that our first and foremost “mission” is to provide code to any and all comers, and for whatever purpose, so that the code gets the widest possible use and provides the widest possible benefit. This, we believe, is one of the most fundamental goals of Free Software and one that we enthusiastically support.

Code in our source tree which falls under the GNU General Public License (GPL) or GNU Library General Public License (LGPL) comes with slightly more strings attached, though at least on the side of enforced access rather than the usual opposite. Due to the additional complexities that can evolve in the commercial use of GPL software, we do, however, endeavor to replace such software with submissions under the more relaxed FreeBSD license whenever possible.

For most people, yes. But this question is not quite that cut-and-dried.

Most people do not actually use an operating system. They use applications. The applications are what really use the operating system. FreeBSD is designed to provide a robust and full-featured environment for applications. It supports a wide variety of web browsers, office suites, email readers, graphics programs, programming environments, network servers, and much more. Most of these applications can be managed through the Ports Collection.

If an application is only available on one operating system, that operating system cannot just be replaced. Chances are, there is a very similar application on FreeBSD, however. As a solid office or Internet server or a reliable workstation, FreeBSD will almost certainly do everything you need. Many computer users across the world, including both novices and experienced UNIX® administrators, use FreeBSD as their only desktop operating system.

Users migrating to FreeBSD from another UNIX®-like environment will find FreeBSD to be similar. Windows® and Mac OS® users may be interested in instead using GhostBSD, MidnightBSD or NomadBSD three FreeBSD-based desktop distributions. Non-UNIX® users should expect to invest some additional time learning the UNIX® way of doing things. This FAQ and the FreeBSD Handbook are excellent places to start.

It is worth pointing out that the word “free” is being used in two ways here: one meaning “at no cost” and the other meaning “do whatever you like”. Apart from one or two things you cannot do with the FreeBSD code, for example pretending you wrote it, you can really do whatever you like with it.

James Howard wrote a good explanation of the history and differences between the various projects, called The BSD Family Tree which goes a fair way to answering this question. Some of the information is out of date, but the history portion in particular remains accurate.

Most of the BSDs share patches and code, even today. All of the BSDs have common ancestry.

The design goals of FreeBSD are described in Q: 1.2, above. The design goals of the other most popular BSDs may be summarized as follows:

At any point in the development of FreeBSD, there can be multiple parallel branches. 12.X releases are made from the 12-STABLE branch, and 11.X releases are made from the 11-STABLE branch.

Up until the release of 12.0, the 11.X series was the one known as -STABLE. However, as of 13.X, the 11.X branch will be designated for an “extended support” status and receive only fixes for major problems, such as security-related fixes.

Releases are made every few months. While many people stay more up-to-date with the FreeBSD sources (see the questions on FreeBSD-CURRENT and FreeBSD-STABLE) than that, doing so is more of a commitment, as the sources are a moving target.

More information on FreeBSD releases can be found on the Release Engineering page and in release(7).

FreeBSD-CURRENT is the development version of the operating system, which will in due course become the new FreeBSD-STABLE branch. As such, it is really only of interest to developers working on the system and die-hard hobbyists. See the relevant section in the Handbook for details on running -CURRENT.

Users not familiar with FreeBSD should not use FreeBSD-CURRENT. This branch sometimes evolves quite quickly and due to mistake can be un-buildable at times. People that use FreeBSD-CURRENT are expected to be able to analyze, debug, and report problems.

FreeBSD-STABLE is the development branch from which major releases are made. Changes go into this branch at a slower pace and with the general assumption that they have first been tested in FreeBSD-CURRENT. However, at any given time, the sources for FreeBSD-STABLE may or may not be suitable for general use, as it may uncover bugs and corner cases that were not yet found in FreeBSD-CURRENT. Users who do not have the resources to perform testing should instead run the most recent release of FreeBSD. FreeBSD-CURRENT, on the other hand, has been one unbroken line since 2.0 was released.

For more detailed information on branches see “FreeBSD Release Engineering: Creating the Release Branch”, the status of the branches and the upcoming release schedule can be found on the Release Engineering Information page.

Version 12.1 is the latest release from the 12-STABLE branch; it was released in November 2019. Version 11.3 is the latest release from the 11-STABLE branch; it was released in July 2019.

The Release Engineering Team <re@FreeBSD.org> releases a new major version of FreeBSD about every 18 months and a new minor version about every 8 months, on average. Release dates are announced well in advance, so that the people working on the system know when their projects need to be finished and tested. A testing period precedes each release, to ensure that the addition of new features does not compromise the stability of the release. Many users regard this caution as one of the best things about FreeBSD, even though waiting for all the latest goodies to reach -STABLE can be a little frustrating.

More information on the release engineering process (including a schedule of upcoming releases) can be found on the release engineering pages on the FreeBSD Web site.

For people who need or want a little more excitement, binary snapshots are made weekly as discussed above.

FreeBSD snapshot releases are made based on the current state of the -CURRENT and -STABLE branches. The goals behind each snapshot release are:

No claims are made that any -CURRENT snapshot can be considered “production quality” for any purpose. If a stable and fully tested system is needed, stick to full releases.

Snapshot releases are directly available from snapshot.

Official snapshots are generated on a regular basis for all actively developed branches.

The key decisions concerning the FreeBSD project, such as the overall direction of the project and who is allowed to add code to the source tree, are made by a core team of 9 people. There is a much larger team of more than 350 committers who are authorized to make changes directly to the FreeBSD source tree.

However, most non-trivial changes are discussed in advance in the mailing lists, and there are no restrictions on who may take part in the discussion.

Every significant release of FreeBSD is available via anonymous FTP from the FreeBSD FTP site:

Information about obtaining FreeBSD on CD, DVD, and other media can be found in the Handbook.

The Problem Report database of all user change requests may be queried by using our web-based PR query interface.

The web-based problem report submission interface can be used to submit problem reports through a web browser.

Before submitting a problem report, read Writing FreeBSD Problem Reports, an article on how to write good problem reports.

The project produces a wide range of documentation, available online from this link: https://www.FreeBSD.org/docs.html.

Yes. The documentation is available in a number of different formats and compression schemes on the FreeBSD FTP site, in the /ftp/doc/ directory.

The documentation is categorized in a number of different ways. These include:

After choosing the format and compression mechanism, download the compressed files, uncompress them, and then copy the appropriate documents into place.

For example, the split HTML version of the FAQ, compressed using bzip2(1), can be found in doc/en_US.ISO8859-1/books/faq/book.html-split.tar.bz2 To download and uncompress that file, type:

# fetch https://download.freebsd.org/ftp/doc/en_US.ISO8859-1/books/faq/book.html-split.tar.bz2
# tar xvf book.html-split.tar.bz2

If the file is compressed, tar will automatically detect the appropriate format and decompress it correctly, resulting in a collection of .html files. The main one is called index.html, which will contain the table of contents, introductory material, and links to the other parts of the document.

Refer to the Handbook entry on mailing-lists and the Handbook entry on newsgroups.

Yes, most major IRC networks host a FreeBSD chat channel:

The FreeBSD wiki has a good list of IRC channels.

Each of these channels are distinct and are not connected to each other. Since their chat styles differ, try each to find one suited to your chat style.

The official FreeBSD forums are located at https://forums.FreeBSD.org/.

iXsystems, Inc., parent company of the FreeBSD Mall, provides commercial FreeBSD and TrueOS software support, in addition to FreeBSD development and tuning solutions.

BSD Certification Group, Inc. provides system administration certifications for DragonFly BSD, FreeBSD, NetBSD, and OpenBSD. Refer to their site for more information.

Any other organizations providing training and support should contact the Project to be listed here.

amd64 is the term FreeBSD uses for 64-bit compatible x86 architectures (also known as "x86-64" or "x64"). Most modern computers should use amd64. Older hardware should use i386. When installing on a non-x86-compatible architecture, select the platform which best matches the hardware.

On the Getting FreeBSD page, select [iso] next to the architecture that matches the hardware.

Any of the following can be used:

Full instructions on this procedure and a little bit more about installation issues in general can be found in the Handbook entry on installing FreeBSD.

This can be caused by not downloading the image in binary mode when using FTP.

Some FTP clients default their transfer mode to ascii and attempt to change any end-of-line characters received to match the conventions used by the client's system. This will almost invariably corrupt the boot image. Check the SHA-256 checksum of the downloaded boot image: if it is not exactly that on the server, then the download process is suspect.

When using a command line FTP client, type binary at the FTP command prompt after getting connected to the server and before starting the download of the image.

Installation instructions can be found at Handbook entry on installing FreeBSD.

Customized FreeBSD installation media can be created by building a custom release. Follow the instructions in the Release Engineering article.

If Windows® is installed first, then yes. FreeBSD's boot manager will then manage to boot Windows® and FreeBSD. If Windows® is installed afterwards, it will overwrite the boot manager. If that happens, see the next section.

This depends upon the boot manager. The FreeBSD boot selection menu can be reinstalled using boot0cfg(8). For example, to restore the boot menu onto the disk ada0:

# boot0cfg -B ada0

The non-interactive MBR bootloader can be installed using gpart(8):

# gpart bootcode -b /boot/mbr ada0

For more complex situations, including GPT disks, see gpart(8).

In general, no. There is nothing in the base system which requires the presence of the source to operate. Some ports, like sysutils/lsof, will not build unless the source is installed. In particular, if the port builds a kernel module or directly operates on kernel structures, the source must be installed.

Usually not. The supplied GENERIC kernel contains the drivers an ordinary computer will need. freebsd-update(8), the FreeBSD binary upgrade tool, cannot upgrade custom kernels, another reason to stick with the GENERIC kernel when possible. For computers with very limited RAM, such as embedded systems, it may be worthwhile to build a smaller custom kernel containing just the required drivers.

FreeBSD uses SHA512 by default. DES passwords are still available for backwards compatibility with operating systems that still use the less secure password format. FreeBSD also supports the Blowfish and MD5 password formats. Which password format to use for new passwords is controlled by the passwd_format login capability in /etc/login.conf, which takes values of des, blf (if these are available) or md5. See the login.conf(5) manual page for more information about login capabilities.

For FFS file systems, the largest file system is practically limited by the amount of memory required to fsck(8) the file system. fsck(8) requires one bit per fragment, which with the default fragment size of 4 KB equates to 32 MB of memory per TB of disk. This does mean that on architectures which limit userland processes to 2 GB (e.g., i386™), the maximum fsck(8)'able filesystem is ~60 TB.

If there was not a fsck(8) memory limit the maximum filesystem size would be 2 ^ 64 (blocks) * 32 KB => 16 Exa * 32 KB => 512 ZettaBytes.

The maximum size of a single FFS file is approximately 2 PB with the default block size of 32 KB. Each 32 KB block can point to 4096 blocks. With triple indirect blocks, the calculation is 32 KB * 12 + 32 KB * 4096 + 32 KB * 4096^2 + 32 KB * 4096^3. Increasing the block size to 64 KB will increase the max file size by a factor of 16.

The world and kernel are out of sync. This is not supported. Be sure to use make buildworld and make buildkernel to update the kernel.

Boot the system by specifying the kernel directly at the second stage, pressing any key when the | shows up before loader is started.

Yes. bsdconfig provides a nice interface to configure FreeBSD post-installation.

The most likely reason is the difference between physical memory addresses and virtual addresses.

The convention for most PC hardware is to use the memory area between 3.5 GB and 4 GB for a special purpose (usually for PCI). This address space is used to access PCI hardware. As a result real, physical memory cannot be accessed by that address space.

What happens to the memory that should appear in that location is hardware dependent. Unfortunately, some hardware does nothing and the ability to use that last 500 MB of RAM is entirely lost.

Luckily, most hardware remaps the memory to a higher location so that it can still be used. However, this can cause some confusion when watching the boot messages.

On a 32-bit version of FreeBSD, the memory appears lost, since it will be remapped above 4 GB, which a 32-bit kernel is unable to access. In this case, the solution is to build a PAE enabled kernel. See the entry on memory limits for more information.

On a 64-bit version of FreeBSD, or when running a PAE-enabled kernel, FreeBSD will correctly detect and remap the memory so it is usable. During boot, however, it may seem as if FreeBSD is detecting more memory than the system really has, due to the described remapping. This is normal and the available memory will be corrected as the boot process completes.

Signal 11 errors are caused when a process has attempted to access memory which the operating system has not granted it access to. If something like this is happening at seemingly random intervals, start investigating the cause.

These problems can usually be attributed to either:

It is probably not a FreeBSD bug if the problem occurs compiling a program, but the activity that the compiler is carrying out changes each time.

For example, if make buildworld fails while trying to compile ls.c into ls.o and, when run again, it fails in the same place, this is a broken build. Try updating source and try again. If the compile fails elsewhere, it is almost certainly due to hardware.

In the first case, use a debugger such as gdb(1) to find the point in the program which is attempting to access a bogus address and fix it.

In the second case, verify which piece of hardware is at fault.

Common causes of this include:

Read the section on Signal 11 for a further explanation and a discussion on how memory testing software or hardware can still pass faulty memory. There is an extensive FAQ on this at the SIG11 problem FAQ.

Finally, if none of this has helped, it is possibly a bug in FreeBSD. Follow these instructions to send a problem report.

The FreeBSD developers are interested in these errors, but need more information than just the error message. Copy the full crash message. Then consult the FAQ section on kernel panics, build a debugging kernel, and get a backtrace. This might sound difficult, but does not require any programming skills. Just follow the instructions.

The FreeBSD kernel will only allow a certain number of processes to exist at one time. The number is based on the kern.maxusers sysctl(8) variable. kern.maxusers also affects various other in-kernel limits, such as network buffers. If the machine is heavily loaded, increase kern.maxusers. This will increase these other system limits in addition to the maximum number of processes.

To adjust the kern.maxusers value, see the File/Process Limits section of the Handbook. While that section refers to open files, the same limits apply to processes.

If the machine is lightly loaded but running a very large number of processes, adjust the kern.maxproc tunable by defining it in /boot/loader.conf. The tunable will not get adjusted until the system is rebooted. For more information about tuning tunables, see loader.conf(5). If these processes are being run by a single user, adjust kern.maxprocperuid to be one less than the new kern.maxproc value. It must be at least one less because one system program, init(8), must always be running.

The remote machine may be setting the terminal type to something other than xterm which is required by the FreeBSD console. Alternatively the kernel may have the wrong values for the width and height of the terminal.

Check the value of the TERM environment variable is xterm. If the remote machine does not support that try vt100.

Run stty -a to check what the kernel thinks the terminal dimensions are. If they are incorrect, they can be changed by running stty rows RR cols CC.

Alternatively, if the client machine has x11/xterm installed, then running resize will query the terminal for the correct dimensions and set them.

The symptom: there is a long delay between the time the TCP connection is established and the time when the client software asks for a password (or, in telnet(1)'s case, when a login prompt appears).

The problem: more likely than not, the delay is caused by the server software trying to resolve the client's IP address into a hostname. Many servers, including the Telnet and SSH servers that come with FreeBSD, do this to store the hostname in a log file for future reference by the administrator.

The remedy: if the problem occurs whenever connecting the client computer to any server, the problem is with the client. If the problem only occurs when someone connects to the server computer, the problem is with the server.

If the problem is with the client, the only remedy is to fix the DNS so the server can resolve it. If this is on a local network, consider it a server problem and keep reading. If this is on the Internet, contact your ISP.

If the problem is with the server on a local network, configure the server to resolve address-to-hostname queries for the local address range. See hosts(5) and named(8) for more information. If this is on the Internet, the problem may be that the local server's resolver is not functioning correctly. To check, try to look up another host such as www.yahoo.com. If it does not work, that is the problem.

Following a fresh install of FreeBSD, it is also possible that domain and name server information is missing from /etc/resolv.conf. This will often cause a delay in SSH, as the option UseDNS is set to yes by default in /etc/ssh/sshd_config. If this is causing the problem, either fill in the missing information in /etc/resolv.conf or set UseDNS to no in sshd_config as a temporary workaround.

This error message indicates that the number of available file descriptors have been exhausted on the system. Refer to the kern.maxfiles section of the Tuning Kernel Limits section of the Handbook for a discussion and solution.

The computer has two or more clocks, and FreeBSD has chosen to use the wrong one.

Run dmesg(8), and check for lines that contain Timecounter. The one with the highest quality value that FreeBSD chose.

# dmesg | grep Timecounter
Timecounter "i8254" frequency 1193182 Hz quality 0
Timecounter "ACPI-fast" frequency 3579545 Hz quality 1000
Timecounter "TSC" frequency 2998570050 Hz quality 800
Timecounters tick every 1.000 msec

Confirm this by checking the kern.timecounter.hardware sysctl(3).

# sysctl kern.timecounter.hardware
kern.timecounter.hardware: ACPI-fast

It may be a broken ACPI timer. The simplest solution is to disable the ACPI timer in /boot/loader.conf:

debug.acpi.disabled="timer"

Or the BIOS may modify the TSC clock—perhaps to change the speed of the processor when running from batteries, or going into a power saving mode, but FreeBSD is unaware of these adjustments, and appears to gain or lose time.

In this example, the i8254 clock is also available, and can be selected by writing its name to the kern.timecounter.hardware sysctl(3).

# sysctl kern.timecounter.hardware=i8254
kern.timecounter.hardware: TSC -> i8254

The computer should now start keeping more accurate time.

To have this change automatically run at boot time, add the following line to /etc/sysctl.conf:

kern.timecounter.hardware=i8254

This means that a process is trying to page memory from disk, and the page attempt has hung trying to access the disk for more than 20 seconds. It might be caused by bad blocks on the disk drive, disk wiring, cables, or any other disk I/O-related hardware. If the drive itself is bad, disk errors will appear in /var/log/messages and in the output of dmesg. Otherwise, check the cables and connections.

The FreeBSD kernel uses a number of resource locks to arbitrate contention for certain resources. When multiple kernel threads try to obtain multiple resource locks, there's always the potential for a deadlock, where two threads have each obtained one of the locks and blocks forever waiting for the other thread to release one of the other locks. This sort of locking problem can be avoided if all threads obtain the locks in the same order.

A run-time lock diagnostic system called witness(4), enabled in FreeBSD-CURRENT and disabled by default for stable branches and releases, detects the potential for deadlocks due to locking errors, including errors caused by obtaining multiple resource locks with a different order from different parts of the kernel. The witness(4) framework tries to detect this problem as it happens, and reports it by printing a message to the system console about a lock order reversal (often referred to also as LOR).

It is possible to get false positives, as witness(4) is conservative. A true positive report does not mean that a system is dead-locked; instead it should be understood as a warning that a deadlock could have happened here.

This means that a function that may sleep was called while a mutex (or other unsleepable) lock was held.

The reason this is an error is because mutexes are not intended to be held for long periods of time; they are supposed to only be held to maintain short periods of synchronization. This programming contract allows device drivers to use mutexes to synchronize with the rest of the kernel during interrupts. Interrupts (under FreeBSD) may not sleep. Hence it is imperative that no subsystem in the kernel block for an extended period while holding a mutex.

To catch such errors, assertions may be added to the kernel that interact with the witness(4) subsystem to emit a warning or fatal error (depending on the system configuration) when a potentially blocking call is made while holding a mutex.

In summary, such warnings are non-fatal, however with unfortunate timing they could cause undesirable effects ranging from a minor blip in the system's responsiveness to a complete system lockup.

For additional information about locking in FreeBSD see locking(9).

This error does not mean that the touch(1) utility is missing. The error is instead probably due to the dates of the files being set sometime in the future. If the CMOS clock is set to local time, run adjkerntz -i to adjust the kernel clock when booting into single-user mode.

Refer to the ports page for info on software packages ported to FreeBSD.

Most ports should work on all supported versions of FreeBSD. Those that do not are specifically marked as such. Each time a FreeBSD release is made, a snapshot of the ports tree at the time of release is also included in the ports/ directory.

FreeBSD supports compressed binary packages to easily install and uninstall ports. Use pkg(7) to control the installation of packages.

Any of the methods listed here work:

If the installed FreeBSD version lags significantly behind -CURRENT or -STABLE, update the Ports Collection using the instructions in Using the Ports Collection. If the system is up-to-date, someone might have committed a change to the port which works for -CURRENT but which broke the port for -STABLE. Submit a bug report, since the Ports Collection is supposed to work for both the -CURRENT and -STABLE branches.

First, make sure that the Ports Collection is up-to-date. Errors that affect building INDEX from an up-to-date copy of the Ports Collection are high-visibility and are thus almost always fixed immediately.

There are rare cases where INDEX will not build due to odd cases involving OPTIONS_SET being set in make.conf. If you suspect that this is the case, try to make INDEX with those variables turned off before reporting it to FreeBSD ports mailing list.

FreeBSD does not include a port upgrading tool, but it does have some tools to make the upgrade process somewhat easier. Additional tools are available to simplify port handling and are described the Upgrading Ports section in the FreeBSD Handbook.

Yes! While a recent system will run with software compiled under an older release, things will randomly crash and fail to work once other ports are installed or updated.

When the system is upgraded, various shared libraries, loadable modules, and other parts of the system will be replaced with newer versions. Applications linked against the older versions may fail to start or, in other cases, fail to function properly.

For more information, see the section on upgrades in the FreeBSD Handbook.

In general, no. FreeBSD developers do their utmost to guarantee binary compatibility across all releases with the same major version number. Any exceptions will be documented in the Release Notes, and advice given there should be followed.

Many people need to write shell scripts which will be portable across many systems. That is why POSIX® specifies the shell and utility commands in great detail. Most scripts are written in Bourne shell (sh(1)), and because several important programming interfaces (make(1), system(3), popen(3), and analogues in higher-level scripting languages like Perl and Tcl) are specified to use the Bourne shell to interpret commands. As the Bourne shell is so often and widely used, it is important for it to be quick to start, be deterministic in its behavior, and have a small memory footprint.

The existing implementation is our best effort at meeting as many of these requirements simultaneously as we can. To keep /bin/sh small, we have not provided many of the convenience features that other shells have. That is why other more featureful shells like bash, scsh, tcsh(1), and zsh are available. Compare the memory utilization of these shells by looking at the “VSZ” and “RSS” columns in a ps -u listing.

Not at all! Check out the kernel config section of the Handbook.

GENERIC kernels shipped with FreeBSD are compiled in debug mode. Kernels built in debug mode contain debug data in separate files that are used for debugging. FreeBSD releases prior to 11.0 store these debug files in the same directory as the kernel itself, /boot/kernel/. In FreeBSD 11.0 and later the debug files are stored in /usr/lib/debug/boot/kernel/. Note that there will be little or no performance loss from running a debug kernel, and it is useful to keep one around in case of a system panic.

When running low on disk space, there are different options to reduce the size of /boot/kernel/ and /usr/lib/debug/.

To not install the symbol files, make sure the following line exists in /etc/src.conf:

WITHOUT_KERNEL_SYMBOLS=yes

For more information see src.conf(5).

If you want to avoid building debug files altogether, make sure that both of the following are true:

Either of the above settings will cause the kernel to be built in debug mode.

To build and install only the specified modules, list them in /etc/make.conf:

MODULES_OVERRIDE= accf_http ipfw

Replace accf_httpd ipfw with a list of needed modules. Only the listed modules will be built. This reduces the size of the kernel directory and decreases the amount of time needed to build the kernel. For more information, read /usr/share/examples/etc/make.conf.

Unneeded devices can be removed from the kernel to further reduce the size. See Q: 7.1 for more information.

To put any of these options into effect, follow the instructions to build and install the new kernel.

For reference, the FreeBSD 11 amd64 kernel (/boot/kernel/kernel) is approximately 25 MB.

There are a number of possible causes for this problem:

The name of the scheduler currently being used is directly available as the value of the kern.sched.name sysctl:

% sysctl kern.sched.name
kern.sched.name: ULE

kern.sched.quantum is the maximum number of ticks a process can run without being preempted in the 4BSD scheduler.

See the Adding Disks section in the FreeBSD Handbook.

The best way is to reinstall the operating system on the new disk, then move the user data over. This is highly recommended when tracking -STABLE for more than one release or when updating a release instead of installing a new one. Install booteasy on both disks with boot0cfg(8) and dual boot until you are happy with the new configuration. Skip the next paragraph to find out how to move the data after doing this.

Alternatively, partition and label the new disk with either sade(8) or gpart(8). If the disks are MBR-formatted, booteasy can be installed on both disks with boot0cfg(8) so that the computer can dual boot to the old or new system after the copying is done.

Once the new disk set up, the data cannot just be copied. Instead, use tools that understand device files and system flags, such as dump(8). Although it is recommended to move the data while in single-user mode, it is not required.

When the disks are formatted with UFS, never use anything but dump(8) and restore(8) to move the root file system. These commands should also be used when moving a single partition to another empty partition. The sequence of steps to use dump to move the data from one UFS partitions to a new partition is:

For example, to move /dev/ada1s1a with /mnt as the temporary mount point, type:

# newfs /dev/ada1s1a
# mount /dev/ada1s1a /mnt
# cd /mnt
# dump 0af - / | restore rf -

Rearranging partitions with dump takes a bit more work. To merge a partition like /var into its parent, create the new partition large enough for both, move the parent partition as described above, then move the child partition into the empty directory that the first move created:

# newfs /dev/ada1s1a
# mount /dev/ada1s1a /mnt
# cd /mnt
# dump 0af - / | restore rf -
# cd var
# dump 0af - /var | restore rf -

To split a directory from its parent, say putting /var on its own partition when it was not before, create both partitions, then mount the child partition on the appropriate directory in the temporary mount point, then move the old single partition:

# newfs /dev/ada1s1a
# newfs /dev/ada1s1d
# mount /dev/ada1s1a /mnt
# mkdir /mnt/var
# mount /dev/ada1s1d /mnt/var
# cd /mnt
# dump 0af - / | restore rf -

The cpio(1) and pax(1) utilities are also available for moving user data. These are known to lose file flag information, so use them with caution.

Short answer: Soft Updates can usually be safely used on all partitions.

Long answer: Soft Updates has two characteristics that may be undesirable on certain partitions. First, a Soft Updates partition has a small chance of losing data during a system crash. The partition will not be corrupted as the data will simply be lost. Second, Soft Updates can cause temporary space shortages.

When using Soft Updates, the kernel can take up to thirty seconds to write changes to the physical disk. When a large file is deleted the file still resides on disk until the kernel actually performs the deletion. This can cause a very simple race condition. Suppose one large file is deleted and another large file is immediately created. The first large file is not yet actually removed from the physical disk, so the disk might not have enough room for the second large file. This will produce an error that the partition does not have enough space, even though a large chunk of space has just been released. A few seconds later, the file creation works as expected.

If a system should crash after the kernel accepts a chunk of data for writing to disk, but before that data is actually written out, data could be lost. This risk is extremely small, but generally manageable.

These issues affect all partitions using Soft Updates. So, what does this mean for the root partition?

Vital information on the root partition changes very rarely. If the system crashed during the thirty-second window after such a change is made, it is possible that data could be lost. This risk is negligible for most applications, but be aware that it exists. If the system cannot tolerate this much risk, do not use Soft Updates on the root file system!

/ is traditionally one of the smallest partitions. If /tmp is on /, there may be intermittent space problems. Symlinking /tmp to /var/tmp will solve this problem.

Finally, dump(8) does not work in live mode (-L) on a filesystem, with Journaled Soft Updates (SU+J).

FreeBSD supports a variety of other file systems.

FreeBSD includes the Network File System NFS and the FreeBSD Ports Collection provides several FUSE applications to support many other file systems.

The secondary DOS partitions are found after all the primary partitions. For example, if E is the second DOS partition on the second SCSI drive, there will be a device file for “slice 5” in /dev. To mount it:

# mount -t msdosfs /dev/da1s5 /dos/e

Yes, gbde(8) and geli(8). See the Encrypting Disk Partitions section of the FreeBSD Handbook.

To boot FreeBSD using GRUB, add the following to either /boot/grub/menu.lst or /boot/grub/grub.conf, depending upon which is used by the Linux® distribution.

title FreeBSD 9.1
	root (hd0,a)
	kernel /boot/loader

Where hd0,a points to the root partition on the first disk. To specify the slice number, use something like this (hd0,2,a). By default, if the slice number is omitted, GRUB searches the first slice which has the a partition.

Install LILO at the start of the Linux® boot partition instead of in the Master Boot Record. Then boot LILO from BootEasy.

This is recommended when running Windows® and Linux® as it makes it simpler to get Linux® booting again if Windows® is reinstalled.

This cannot be accomplished with the standard boot manager without rewriting it. There are a number of other boot managers in the sysutils category of the Ports Collection.

If the drive already has a file system on it, use a command like this:

# mount -t msdosfs /dev/da0s1 /mnt

If the drive will only be used with FreeBSD systems, partition it with UFS or ZFS. This will provide long filename support, improvement in performance, and stability. If the drive will be used by other operating systems, a more portable choice, such as msdosfs, is better.

# dd if=/dev/zero of=/dev/da0 count=2
# gpart create -s GPT /dev/da0
# gpart add -t freebsd-ufs /dev/da0

Finally, create a new file system:

# newfs /dev/da0p1

and mount it:

# mount /dev/da0s1 /mnt

It is a good idea to add a line to /etc/fstab (see fstab(5)) so you can just type mount /mnt in the future:

/dev/da0p1 /mnt ufs rw,noauto 0 0

The type of device to mount must be specified. This is described in the Handbook section on Using Data CDs.

This generally means that there is no CD in the drive, or the drive is not visible on the bus. Refer to the Using Data CDs section of the Handbook for a detailed discussion of this issue.

The CD probably uses the “Joliet” extension for storing information about files and directories. This is discussed in the Handbook section on Using Data CD-ROMs.

This means a raw file was burned to the CD, rather than creating an ISO 9660 file system. Take a look at the Handbook section on Using Data CDs.

This is discussed in the Handbook section on Writing Data to an ISO File System. For more on working with CD-ROMs, see the Creating CDs Section in the Storage chapter in the Handbook.

Trying to mount an audio CD will produce an error like cd9660: /dev/cd0: Invalid argument. This is because mount only works on file systems. Audio CDs do not have file systems; they just have data. Instead, use a program that reads audio CDs, such as the audio/xmcd package or port.

By default, mount(8) will attempt to mount the last data track (session) of a CD. To load an earlier session, use the -s command line argument. Refer to mount_cd9660(8) for specific examples.

As root set the sysctl variable vfs.usermount to 1.

# sysctl vfs.usermount=1

To make this persist across reboots, add the line vfs.usermount=1 to /etc/sysctl.conf so that it is reset at system boot time.

Users can only mount devices they have read permissions to. To allow users to mount a device permissions must be set in /etc/devfs.conf.

For example, to allow users to mount the first USB drive add:

# Allow all users to mount a USB drive.
	    own       /dev/da0       root:operator
	    perm      /dev/da0       0666

All users can now mount devices they could read onto a directory that they own:

% mkdir ~/my-mount-point
% mount -t msdosfs /dev/da0 ~/my-mount-point

Unmounting the device is simple:

% umount ~/my-mount-point

Enabling vfs.usermount, however, has negative security implications. A better way to access MS-DOS® formatted media is to use the emulators/mtools package in the Ports Collection.

This is due to how these commands actually work. du goes through the directory tree, measures how large each file is, and presents the totals. df just asks the file system how much space it has left. They seem to be the same thing, but a file without a directory entry will affect df but not du.

When a program is using a file, and the file is deleted, the file is not really removed from the file system until the program stops using it. The file is immediately deleted from the directory listing, however. As an example, consider a file large enough to affect the output of du and df. A file being viewed with more can be deleted wihout causing an error. The entry is removed from the directory so no other program or user can access it. However, du shows that it is gone as it has walked the directory tree and the file is not listed. df shows that it is still there, as the file system knows that more is still using that space. Once the more session ends, du and df will agree.

This situation is common on web servers. Many people set up a FreeBSD web server and forget to rotate the log files. The access log fills up /var. The new administrator deletes the file, but the system still complains that the partition is full. Stopping and restarting the web server program would free the file, allowing the system to release the disk space. To prevent this from happening, set up newsyslog(8).

Note that Soft Updates can delay the freeing of disk space and it can take up to 30 seconds for the change to be visible.

This section of the Handbook describes how to do this.

Disk manufacturers calculate gigabytes as a billion bytes each, whereas FreeBSD calculates them as 1,073,741,824 bytes each. This explains why, for example, FreeBSD's boot messages will report a disk that supposedly has 80 GB as holding 76,319 MB.

Also note that FreeBSD will (by default) reserve 8% of the disk space.

A portion of each UFS partition (8%, by default) is reserved for use by the operating system and the root user. df(1) does not count that space when calculating the Capacity column, so it can exceed 100%. Notice that the Blocks column is always greater than the sum of the Used and Avail columns, usually by a factor of 8%.

For more details, look up -m in tunefs(8).

A minimum of 4GB of RAM is required for comfortable usage, but individual workloads can vary widely.

The ZIL (ZFS intent log) is a write log used to implement posix write commitment semantics across crashes. Normally writes are bundled up into transaction groups and written to disk when filled (“Transaction Group Commit”). However syscalls like fsync(2) require a commitment that the data is written to stable storage before returning. The ZIL is needed for writes that have been acknowledged as written but which are not yet on disk as part of a transaction. The transaction groups are timestamped. In the event of a crash the last valid timestamp is found and missing data is merged in from the ZIL.

By default, ZFS stores the ZIL in the pool with all the data. If an application has a heavy write load, storing the ZIL in a separate device that has very fast synchronous, sequential write performance can improve overall system performance. For other workloads, a SSD is unlikely to make much of an improvement.

The L2ARC is a read cache stored on a fast device such as an SSD. This cache is not persistent across reboots. Note that RAM is used as the first layer of cache and the L2ARC is only needed if there is insufficient RAM.

L2ARC needs space in the ARC to index it. So, perversely, a working set that fits perfectly in the ARC will not fit perfectly any more if a L2ARC is used because part of the ARC is holding the L2ARC index, pushing part of the working set into the L2ARC which is slower than RAM.

Generally speaking, no.

Deduplication takes up a significant amount of RAM and may slow down read and write disk access times. Unless one is storing data that is very heavily duplicated, such as virtual machine images or user backups, it is possible that deduplication will do more harm than good. Another consideration is the inability to revert deduplication status. If data is written when deduplication is enabled, disabling dedup will not cause those blocks which were deduplicated to be replicated until they are next modified.

Deduplication can also lead to some unexpected situations. In particular, deleting files may become much slower.

This could happen because the pool is 100% full. ZFS requires space on the disk to write transaction metadata. To restore the pool to a usable state, truncate the file to delete:

% truncate -s 0 unimportant-file

File truncation works because a new transaction is not started, new spare blocks are created instead.

ZFS TRIM support was added to FreeBSD 10-CURRENT with revision r240868. ZFS TRIM support was added to all FreeBSD-STABLE branches in r252162 and r251419, respectively.

ZFS TRIM is enabled by default, and can be turned off by adding this line to /etc/sysctl.conf:

vfs.zfs.trim.enabled=0

The primary configuration file is /etc/defaults/rc.conf which is described in rc.conf(5). System startup scripts such as /etc/rc and /etc/rc.d, which are described in rc(8), include this file. Do not edit this file! Instead, to edit an entry in /etc/defaults/rc.conf, copy the line into /etc/rc.conf and change it there.

For example, if to start named(8), the included DNS server:

# echo 'named_enable="YES"' >> /etc/rc.conf

To start up local services, place shell scripts in the /usr/local/etc/rc.d directory. These shell scripts should be set executable, the default file mode is 555.

Use the adduser(8) command, or the pw(8) command for more complicated situations.

To remove the user, use the rmuser(8) command or, if necessary, pw(8).

This is normally caused by editing the system crontab. This is not the correct way to do things as the system crontab has a different format to the per-user crontabs. The system crontab has an extra field, specifying which user to run the command as. cron(8) assumes this user is the first word of the command to execute. Since no such command exists, this error message is displayed.

To delete the extra, incorrect crontab:

# crontab -r

This is a security feature. In order to su to root, or any other account with superuser privileges, the user account must be a member of the wheel group. If this feature were not there, anybody with an account on a system who also found out root's password would be able to gain superuser level access to the system.

To allow someone to su to root, put them in the wheel group using pw:

# pw groupmod wheel -m lisa

The above example will add user lisa to the group wheel.

Restart the system using boot -s at the loader prompt to enter single-user mode. When prompted for a shell pathname, press Enter and run mount -urw / to re-mount the root file system in read/write mode. You may also need to run mount -a -t ufs to mount the file system where your favorite editor is defined. If that editor is on a network file system, either configure the network manually before mounting the network file systems, or use an editor which resides on a local file system, such as ed(1).

In order to use a full screen editor such as vi(1) or emacs(1), run export TERM=xterm so that these editors can load the correct data from the termcap(5) database.

After performing these steps, edit /etc/rc.conf to fix the syntax error. The error message displayed immediately after the kernel boot messages should indicate the number of the line in the file which is at fault.

See the Handbook entry on printing for troubleshooting tips.

Refer to the Handbook section on using localization, specifically the section on console setup.

Yes, FreeBSD supports System V-style IPC, including shared memory, messages and semaphores, in the GENERIC kernel. With a custom kernel, support may be loaded with the sysvshm.ko, sysvsem.ko and sysvmsg.ko kernel modules, or enabled in the custom kernel by adding the following lines to the kernel configuration file:

options    SYSVSHM          # enable shared memory
options    SYSVSEM          # enable for semaphores
options    SYSVMSG          # enable for messaging

Recompile and install the kernel.

The Sendmail server is the default mail-server software for FreeBSD, but it can be replaced with another MTA installed from the Ports Collection. Available ports include mail/exim, mail/postfix, and mail/qmail. Search the mailing lists for discussions regarding the advantages and disadvantages of the available MTAs.

Do not panic! Restart the system, type boot -s at the Boot: prompt to enter single-user mode. At the question about the shell to use, hit Enter which will display a # prompt. Enter mount -urw / to remount the root file system read/write, then run mount -a to remount all the file systems. Run passwd root to change the root password then run exit(1) to continue booting.

When using vt(4), the default console driver, this can be done by setting the following sysctl(8):

# sysctl kern.vt.kbd_reboot=0

Use this perl(1) command:

% perl -i.bak -npe 's/\r\n/\n/g' file(s)

where file(s) is one or more files to process. The modification is done in-place, with the original file stored with a .bak extension.

Alternatively, use tr(1):

% tr -d '\r' < dos-text-file > unix-file

dos-text-file is the file containing DOS text while unix-file will contain the converted output. This can be quite a bit faster than using perl.

Yet another way to reformat DOS text files is to use the converters/dosunix port from the Ports Collection. Consult its documentation about the details.

Go into single-user mode and then back to multi-user mode:

# shutdown now
# return
# exit

Short answer: it is just a name. RC stands for “Release Candidate”. It signifies that a release is imminent. In FreeBSD, -PRERELEASE is typically synonymous with the code freeze before a release. (For some releases, the -BETA label was used in the same way as -PRERELEASE.)

Long answer: FreeBSD derives its releases from one of two places. Major, dot-zero, releases, such as 9.0-RELEASE are branched from the head of the development stream, commonly referred to as -CURRENT. Minor releases, such as 6.3-RELEASE or 5.2-RELEASE, have been snapshots of the active -STABLE branch. Starting with 4.3-RELEASE, each release also now has its own branch which can be tracked by people requiring an extremely conservative rate of development (typically only security advisories).

When a release is about to be made, the branch from which it will be derived from has to undergo a certain process. Part of this process is a code freeze. When a code freeze is initiated, the name of the branch is changed to reflect that it is about to become a release. For example, if the branch used to be called 6.2-STABLE, its name will be changed to 6.3-PRERELEASE to signify the code freeze and signify that extra pre-release testing should be happening. Bug fixes can still be committed to be part of the release. When the source code is in shape for the release the name will be changed to 6.3-RC to signify that a release is about to be made from it. Once in the RC stage, only the most critical bugs found can be fixed. Once the release (6.3-RELEASE in this example) and release branch have been made, the branch will be renamed to 6.3-STABLE.

For more information on version numbers and the various Subversion branches, refer to the Release Engineering article.

Short answer: the security level is greater than 0. Reboot directly to single-user mode to install the kernel.

Long answer: FreeBSD disallows changing system flags at security levels greater than 0. To check the current security level:

# sysctl kern.securelevel

The security level cannot be lowered in multi-user mode, so boot to single-user mode to install the kernel, or change the security level in /etc/rc.conf then reboot. See the init(8) manual page for details on securelevel, and see /etc/defaults/rc.conf and the rc.conf(5) manual page for more information on rc.conf.

Short answer: the system is at a security level greater than 1. Reboot directly to single-user mode to change the date.

Long answer: FreeBSD disallows changing the time by more that one second at security levels greater than 1. To check the security level:

# sysctl kern.securelevel

The security level cannot be lowered in multi-user mode. Either boot to single-user mode to change the date or change the security level in /etc/rc.conf and reboot. See the init(8) manual page for details on securelevel, and see /etc/defaults/rc.conf and the rc.conf(5) manual page for more information on rc.conf.

No, there is no memory leak, and it is not using 256 MB of memory. For convenience, rpc.statd maps an obscene amount of memory into its address space. There is nothing terribly wrong with this from a technical standpoint; it just throws off things like top(1) and ps(1).

rpc.statd(8) maps its status file (resident on /var) into its address space; to save worrying about remapping the status file later when it needs to grow, it maps the status file with a generous size. This is very evident from the source code, where one can see that the length argument to mmap(2) is 0x10000000, or one sixteenth of the address space on an IA32, or exactly 256 MB.

The system is running at securelevel greater than 0. Lower the securelevel and try again. For more information, see the FAQ entry on securelevel and the init(8) manual page.

vnlru flushes and frees vnodes when the system hits the kern.maxvnodes limit. This kernel thread sits mostly idle, and only activates when there is a huge amount of RAM and users are accessing tens of thousands of tiny files.

Pages are most often written to disk (sort of a VM sync) when they are in the laundry state, but active or inactive pages can also be synced. This depends upon the CPU tracking of the modified bit being available, and in certain situations there can be an advantage for a block of VM pages to be synced, regardless of the queue they belong to. In most common cases, it is best to think of the laundry queue as a queue of relatively unused pages that might or might not be in the process of being written to disk. The inactive queue contains a mix of clean and dirty pages; clean pages near the head of the queue are reclaimed immediately to alleviate a free page shortage, and dirty pages are moved to the laundry queue for deferred processing.

There are some other flags (e.g., busy flag or busy count) that might modify some of the described rules.

There are a couple of kinds of “free memory”. The most common is the amount of memory immediately available without reclaiming memory already in use. That is the size of the free pages queue plus some other reserved pages. This amount is exported by the vm.stats.vm.v_free_count sysctl(8), shown, for instance, by top(1). Another kind of “free memory” is the total amount of virtual memory available to userland processes, which depends on the sum of swap space and usable memory. Other kinds of “free memory” descriptions are also possible, but it is relatively useless to define these, but rather it is important to make sure that the paging rate is kept low, and to avoid running out of swap space.

/var/empty is a directory that the sshd(8) program uses when performing privilege separation. The /var/empty directory is empty, owned by root and has the schg flag set. This directory should not be deleted.

To see what newsyslog(8) will do, use the following:

% newsyslog -nrvv

Use tzsetup(8).

The X Window System (commonly X11) is the most widely available windowing system capable of running on UNIX® or UNIX® like systems, including FreeBSD. The X.Org Foundation administers the X protocol standards, with the current reference implementation, version 11 release 7.7, so references are often shortened to X11.

Many implementations are available for different architectures and operating systems. An implementation of the server-side code is properly known as an X server.

To install Xorg do one of the following:

Use the x11/xorg meta-port, which builds and installs every Xorg component.

Use x11/xorg-minimal, which builds and installs only the necessary Xorg components.

Install Xorg from FreeBSD packages:

# pkg install xorg

After the installation of Xorg, follow the instructions from the X11 Configuration section of the FreeBSD Handbook.

The system is probably running at a raised securelevel. It is not possible to start X at a raised securelevel because X requires write access to io(4). For more information, see at the init(8) manual page.

There are two solutions to the problem: set the securelevel back down to zero or run xdm(1) (or an alternative display manager) at boot time before the securelevel is raised.

See Q: 11.10 for more information about running xdm(1) at boot time.

When using vt(4), the default console driver, FreeBSD can be configured to support a mouse pointer on each virtual screen. To avoid conflicting with X, vt(4) supports a virtual device called /dev/sysmouse. All mouse events received from the real mouse device are written to the sysmouse(4) device via moused(8). To use the mouse on one or more virtual consoles, and use X, see Q: 4.4.1 and set up moused(8).

Then edit /etc/X11/xorg.conf and make sure the following lines exist:

Section "InputDevice"
   Option          "Protocol" "SysMouse"
   Option          "Device" "/dev/sysmouse"
.....

Starting with Xorg version 7.4, the InputDevice sections in xorg.conf are ignored in favor of autodetected devices. To restore the old behavior, add the following line to the ServerLayout or ServerFlags section:

Option "AutoAddDevices" "false"

Some people prefer to use /dev/mouse under X. To make this work, /dev/mouse should be linked to /dev/sysmouse (see sysmouse(4)) by adding the following line to /etc/devfs.conf (see devfs.conf(5)):

link    sysmouse    mouse

This link can be created by restarting devfs(5) with the following command (as root):

# service devfs restart

Yes, if X is configured for a 5 button mouse. To do this, add the lines Buttons 5 and ZAxisMapping 4 5 to the “InputDevice” section of /etc/X11/xorg.conf, as seen in this example:

Section "InputDevice"
   Identifier      "Mouse1"
   Driver          "mouse"
   Option          "Protocol" "auto"
   Option          "Device" "/dev/sysmouse"
   Option          "Buttons" "5"
   Option          "ZAxisMapping" "4 5"
EndSection

The mouse can be enabled in Emacs by adding these lines to ~/.emacs:

;; wheel mouse
(global-set-key [mouse-4] 'scroll-down)
(global-set-key [mouse-5] 'scroll-up)

Yes, after configuring a few things to make it work.

In order to use the Xorg synaptics driver, first remove moused_enable from rc.conf.

To enable synaptics, add the following line to /boot/loader.conf:

hw.psm.synaptics_support="1"

Add the following to /etc/X11/xorg.conf:

Section "InputDevice"
Identifier  "Touchpad0"
Driver      "synaptics"
Option      "Protocol" "psm"
Option      "Device" "/dev/psm0"
EndSection

And be sure to add the following into the “ServerLayout” section:

InputDevice    "Touchpad0" "SendCoreEvents"

For security reasons, the default setting is to not allow a machine to remotely open a window.

To enable this feature, start X with the optional -listen_tcp argument:

% startx -listen_tcp

Virtual consoles provide several simultaneous sessions on the same machine without doing anything complicated like setting up a network or running X.

When the system starts, it will display a login prompt on the monitor after displaying all the boot messages. Type in your login name and password to start working on the first virtual console.

To start another session, perhaps to look at documentation for a program or to read mail while waiting for an FTP transfer to finish, hold down Alt and press F2. This will display the login prompt for the second virtual console. To go back to the original session, press Alt+F1.

The default FreeBSD installation has eight virtual consoles enabled. Alt+F1, Alt+F2, Alt+F3, and so on will switch between these virtual consoles.

To enable more of virtual consoles, edit /etc/ttys (see ttys(5)) and add entries for ttyv8 to ttyvc, after the comment on “Virtual terminals”:

# Edit the existing entry for ttyv8 in /etc/ttys and change
# "off" to "on".
ttyv8   "/usr/libexec/getty Pc"         xterm  on secure
ttyv9   "/usr/libexec/getty Pc"         xterm  on secure
ttyva   "/usr/libexec/getty Pc"         xterm  on secure
ttyvb   "/usr/libexec/getty Pc"         xterm  on secure

The more virtual terminals, the more resources that are used. This can be problematic on systems with 8 MB RAM or less. Consider changing secure to insecure.

For example, to run X and eleven virtual consoles, the setting for virtual terminal 12 should be:

ttyvb   "/usr/libexec/getty Pc"         xterm  off secure

The easiest way to activate the virtual consoles is to reboot.

Use Ctrl+Alt+Fn to switch back to a virtual console. Press Ctrl+Alt+F1 to return to the first virtual console.

Once at a text console, use Alt+Fn to move between them.

To return to the X session, switch to the virtual console running X. If X was started from the command line using startx, the X session will attach to the next unused virtual console, not the text console from which it was invoked. For eight active virtual terminals, X will run on the ninth, so use Alt+F9.

There are two schools of thought on how to start xdm(1). One school starts xdm from /etc/ttys (see ttys(5)) using the supplied example, while the other runs xdm from rc.local (see rc(8)) or from an X script in /usr/local/etc/rc.d. Both are equally valid, and one may work in situations where the other does not. In both cases the result is the same: X will pop up a graphical login prompt.

The ttys(5) method has the advantage of documenting which vty X will start on and passing the responsibility of restarting the X server on logout to init(8). The rc(8) method makes it easy to kill xdm if there is a problem starting the X server.

If loaded from rc(8), xdm should be started without any arguments. xdm must start after getty(8) runs, or else getty and xdm will conflict, locking out the console. The best way around this is to have the script sleep 10 seconds or so then launch xdm.

When starting xdm from /etc/ttys, there still is a chance of conflict between xdm and getty(8). One way to avoid this is to add the vt number in /usr/local/lib/X11/xdm/Xservers:

:0 local /usr/local/bin/X vt4

The above example will direct the X server to run in /dev/ttyv3. Note the number is offset by one. The X server counts the vty from one, whereas the FreeBSD kernel numbers the vty from zero.

When X is started with startx, the permissions on /dev/console will not get changed, resulting in things like xterm -C and xconsole not working.

This is because of the way console permissions are set by default. On a multi-user system, one does not necessarily want just any user to be able to write on the system console. For users who are logging directly onto a machine with a VTY, the fbtab(5) file exists to solve such problems.

In a nutshell, make sure an uncommented line of the form is in /etc/fbtab (see fbtab(5)):

/dev/ttyv0 0600 /dev/console

It will ensure that whomever logs in on /dev/ttyv0 will own the console.

The mouse and the mouse driver may have become out of synchronization. In rare cases, the driver may also erroneously report synchronization errors:

psmintr: out of sync (xxxx != yyyy)

If this happens, disable the synchronization check code by setting the driver flags for the PS/2 mouse driver to 0x100. This can be easiest achieved by adding hint.psm.0.flags="0x100" to /boot/loader.conf and rebooting.

Type xmodmap -e "pointer = 3 2 1". Add this command to ~/.xinitrc or ~/.xsession to make it happen automatically.

The detailed answer for this question can be found in the Boot Time Splash Screens section of the FreeBSD Handbook.

Yes. Use xmodmap(1) to define which functions the keys should perform.

Assuming all Windows keyboards are standard, the keycodes for these three keys are the following:

To have the left Windows key print a comma, try this.

# xmodmap -e "keycode 115 = comma"

To have the Windows key-mappings enabled automatically every time X is started, either put the xmodmap commands in ~/.xinitrc or, preferably, create a ~/.xmodmaprc and include the xmodmap options, one per line, then add the following line to ~/.xinitrc:

xmodmap $HOME/.xmodmaprc

For example, to map the 3 keys to be F13, F14, and F15, respectively. This would make it easy to map them to useful functions within applications or the window manager.

To do this, put the following in ~/.xmodmaprc.

keycode 115 = F13
keycode 116 = F14
keycode 117 = F15

For the x11-wm/fvwm2 desktop manager, one could map the keys so that F13 iconifies or de-iconifies the window the cursor is in, F14 brings the window the cursor is in to the front or, if it is already at the front, pushes it to the back, and F15 pops up the main Workplace menu even if the cursor is not on the desktop, which is useful when no part of the desktop is visible.

The following entries in ~/.fvwmrc implement the aforementioned setup:

Key F13        FTIWS    A        Iconify
Key F14        FTIWS    A        RaiseLower
Key F15        A        A        Menu Workplace Nop

The availability of 3D acceleration depends on the version of Xorg and the type of video chip. For an nVidia chip, use the binary drivers provided for FreeBSD by installing one of the following ports:

The latest versions of nVidia cards are supported by the x11/nvidia-driver port.

Older drivers are available as x11/nvidia-driver-###

nVidia provides detailed information on which card is supported by which driver on their web site: http://www.nvidia.com/object/IO_32667.html.

For Matrox G200/G400, check the x11-drivers/xf86-video-mga port.

For ATI Rage 128 and Radeon see ati(4), r128(4) and radeon(4).

“Diskless booting” means that the FreeBSD box is booted over a network, and reads the necessary files from a server instead of its hard disk. For full details, see the Handbook entry on diskless booting.

Yes. Refer to the Handbook entry on advanced networking, specifically the section on routing and gateways.

Yes. For instructions on how to use NAT over a PPP connection, see the Handbook entry on PPP. To use NAT over some other sort of network connection, look at the natd section of the Handbook.

If the alias is on the same subnet as an address already configured on the interface, add netmask 0xffffffff to this command:

# ifconfig ed0 alias 192.0.2.2 netmask 0xffffffff

Otherwise, specify the network address and netmask as usual:

# ifconfig ed0 alias 172.16.141.5 netmask 0xffffff00

More information can be found in the FreeBSD Handbook.

Some versions of the Linux® NFS code only accept mount requests from a privileged port; try to issue the following command:

# mount -o -P linuxbox:/blah /mnt

The most frequent problem is not understanding the correct format of /etc/exports. Review exports(5) and the NFS entry in the Handbook, especially the section on configuring NFS.

Install the net/mrouted package or port and add mrouted_enable="YES" to /etc/rc.conf start this service at boot time.

See the answer in the FreeBSD Handbook.

If the kernel is compiled with the IPFIREWALL option, be aware that the default policy is to deny all packets that are not explicitly allowed.

If the firewall is unintentionally misconfigured, restore network operability by typing the following as root:

# ipfw add 65534 allow all from any to any

Consider setting firewall_type="open" in /etc/rc.conf.

For further information on configuring this firewall, see the Handbook chapter.

Possibly because network address translation (NAT) is needed instead of just forwarding packets. A “fwd” rule only forwards packets, it does not actually change the data inside the packet. Consider this rule:

01000 fwd 10.0.0.1 from any to foo 21

When a packet with a destination address of foo arrives at the machine with this rule, the packet is forwarded to 10.0.0.1, but it still has the destination address of foo. The destination address of the packet is not changed to 10.0.0.1. Most machines would probably drop a packet that they receive with a destination address that is not their own. Therefore, using a “fwd” rule does not often work the way the user expects. This behavior is a feature and not a bug.

See the FAQ about redirecting services, the natd(8) manual, or one of the several port redirecting utilities in the Ports Collection for a correct way to do this.

FTP and other service requests can be redirected with the sysutils/socket package or port. Replace the entry for the service in /etc/inetd.conf to call socket, as seen in this example for ftpd:

ftp stream tcp nowait nobody /usr/local/bin/socket socket ftp.example.com ftp

where ftp.example.com and ftp are the host and port to redirect to, respectively.

There are three bandwidth management tools available for FreeBSD. dummynet(4) is integrated into FreeBSD as part of ipfw(4). ALTQ has been integrated into FreeBSD as part of pf(4). Bandwidth Manager from Emerging Technologies is a commercial product.

The running application requires the Berkeley Packet Filter (bpf(4)), but it was removed from a custom kernel. Add this to the kernel config file and build a new kernel:

device bpf        # Berkeley Packet Filter

Use the SMBFS toolset. It includes a set of kernel modifications and a set of userland programs. The programs and information are available as mount_smbfs(8) in the base system.

This kernel message indicates that some activity is provoking it to send a large amount of ICMP or TCP reset (RST) responses. ICMP responses are often generated as a result of attempted connections to unused UDP ports. TCP resets are generated as a result of attempted connections to unopened TCP ports. Among others, these are the kinds of activities which may cause these messages:

The first number in the message indicates how many packets the kernel would have sent if the limit was not in place, and the second indicates the limit. This limit is controlled using net.inet.icmp.icmplim. This example sets the limit to 300 packets per second:

# sysctl net.inet.icmp.icmplim=300

To disable these messages without disabling response limiting, use net.inet.icmp.icmplim_output to disable the output:

# sysctl net.inet.icmp.icmplim_output=0

Finally, to disable response limiting completely, set net.inet.icmp.icmplim to 0. Disabling response limiting is discouraged for the reasons listed above.

This means that some device on the local Ethernet is using a MAC address in a format that FreeBSD does not recognize. This is probably caused by someone experimenting with an Ethernet card somewhere else on the network. This is most commonly seen on cable modem networks. It is harmless, and should not affect the performance of the FreeBSD system.

A packet is coming from outside the network unexpectedly. To disable them, set net.link.ether.inet.log_arp_wrong_iface to 0.

Configure your kernel with these settings:

include GENERIC
ident GENERIC-IPV6ONLY
makeoptions MKMODULESENV+="WITHOUT_INET_SUPPORT="
nooptions INET
nodevice gre

“Sandbox” is a security term. It can mean two things:

UNIX® implements two core sandboxes. One is at the process level, and one is at the userid level.

Every UNIX® process is completely firewalled off from every other UNIX® process. One process cannot modify the address space of another.

A UNIX® process is owned by a particular userid. If the user ID is not the root user, it serves to firewall the process off from processes owned by other users. The user ID is also used to firewall off on-disk data.

securelevel is a security mechanism implemented in the kernel. When the securelevel is positive, the kernel restricts certain tasks; not even the superuser (root) is allowed to do them. The securelevel mechanism limits the ability to:

To check the status of the securelevel on a running system:

# sysctl -n kern.securelevel

The output contains the current value of the securelevel. If it is greater than 0, at least some of the securelevel's protections are enabled.

The securelevel of a running system cannot be lowered as this would defeat its purpose. If a task requires that the securelevel be non-positive, change the kern_securelevel and kern_securelevel_enable variables in /etc/rc.conf and reboot.

For more information on securelevel and the specific things all the levels do, consult init(8).

Do not worry. toor is an “alternative” superuser account, where toor is root spelled backwards. It is intended to be used with a non-standard shell so the default shell for root does not need to change. This is important as shells which are not part of the base distribution, but are instead installed from ports or packages, are installed in /usr/local/bin which, by default, resides on a different file system. If root's shell is located in /usr/local/bin and the file system containing /usr/local/bin) is not mounted, root will not be able to log in to fix a problem and will have to reboot into single-user mode in order to enter the path to a shell.

Some people use toor for day-to-day root tasks with a non-standard shell, leaving root, with a standard shell, for single-user mode or emergencies. By default, a user cannot log in using toor as it does not have a password, so log in as root and set a password for toor before using it to login.

See this section of the Handbook.

As the FreeBSD kernel boots, it will probe for the serial ports for which the kernel is configured. Either watch the boot messages closely or run this command after the system is up and running:

% grep -E '^(sio|uart)[0-9]' < /var/run/dmesg.boot
sio0: <16550A-compatible COM port> port 0x3f8-0x3ff irq 4 flags 0x10 on acpi0
sio0: type 16550A
sio1: <16550A-compatible COM port> port 0x2f8-0x2ff irq 3 on acpi0
sio1: type 16550A

This example shows two serial ports. The first is on IRQ4, port address 0x3f8, and has a 16550A-type UART chip. The second uses the same kind of chip but is on IRQ3 and is at port address 0x2f8. Internal modem cards are treated just like serial ports, except that they always have a modem attached to the port.

The GENERIC kernel includes support for two serial ports using the same IRQ and port address settings in the above example. If these settings are not right for the system, or if there are more modem cards or serial ports than the kernel is configured for, reconfigure using the instructions in building a kernel for more details.

The third serial port, sio2, or COM3, is on /dev/cuad2 for dial-out devices, and on /dev/ttyd2 for dial-in devices. What is the difference between these two classes of devices?

When opening /dev/ttydX in blocking mode, a process will wait for the corresponding cuadX device to become inactive, and then wait for the carrier detect line to go active. When the cuadX device is opened, it makes sure the serial port is not already in use by the ttydX device. If the port is available, it steals it from the ttydX device. Also, the cuadX device does not care about carrier detect. With this scheme and an auto-answer modem, remote users can log in and local users can still dial out with the same modem and the system will take care of all the conflicts.

The section on kernel configuration provides information about configuring the kernel. For a multi-port serial card, place an sio(4) line for each serial port on the card in the device.hints(5) file. But place the IRQ specifiers on only one of the entries. All of the ports on the card should share one IRQ. For consistency, use the last serial port to specify the IRQ. Also, specify the following option in the kernel configuration file:

options COM_MULTIPORT

The following /boot/device.hints example is for an AST 4-port serial card on IRQ 12:

hint.sio.4.at="isa"
hint.sio.4.port="0x2a0"
hint.sio.4.flags="0x701"
hint.sio.5.at="isa"
hint.sio.5.port="0x2a8"
hint.sio.5.flags="0x701"
hint.sio.6.at="isa"
hint.sio.6.port="0x2b0"
hint.sio.6.flags="0x701"
hint.sio.7.at="isa"
hint.sio.7.port="0x2b8"
hint.sio.7.flags="0x701"
hint.sio.7.irq="12"

The flags indicate that the master port has minor number 7 (0x700), and all the ports share an IRQ (0x001).

See the Serial Communications section in the FreeBSD Handbook.

The built-in tip(1) and cu(1) utilities can only access the /var/spool/lock directory via user uucp and group dialer. Use the dialer group to control who has access to the modem or remote systems by adding user accounts to dialer.

Alternatively, everyone can be configured to run tip(1) and cu(1) by typing:

# chmod 4511 /usr/bin/cu
# chmod 4511 /usr/bin/tip

FreeBSD will proactively move entirely idle, unused pages of main memory into swap in order to make more main memory available for active use. This heavy use of swap is balanced by using the extra free memory for caching.

Note that while FreeBSD is proactive in this regard, it does not arbitrarily decide to swap pages when the system is truly idle. Thus, the system will not be all paged out after leaving it idle overnight.

The simple answer is that free memory is wasted memory. Any memory that programs do not actively allocate is used within the FreeBSD kernel as disk cache. The values shown by top(1) labeled as Inact and Laundry are cached data at different aging levels. This cached data means the system does not have to access a slow disk again for data it has accessed recently, thus increasing overall performance. In general, a low value shown for Free memory in top(1) is good, provided it is not very low.

Symlinks do not have permissions, and by default, chmod(1) will follow symlinks to change the permissions on the source file, if possible. For the file, foo with a symlink named bar, this command will always succeed.

% chmod g-w bar

However, the permissions on bar will not have changed.

When changing modes of the file hierarchies rooted in the files instead of the files themselves, use either -H or -L together with -R to make this work. See chmod(1) and symlink(7) for more information.

% chmod 555 foo/

Yes. A DOS emulation program, emulators/doscmd, is available in the FreeBSD Ports Collection.

If doscmd will not suffice, emulators/pcemu emulates an 8088 and enough BIOS services to run many DOS text-mode applications. It requires the X Window System.

The Ports Collection also has emulators/dosbox. The main focus of this application is emulating old DOS games using the local file system for files.

See the Translation FAQ in the FreeBSD Documentation Project Primer.

The FreeBSD.org mail system implements some Postfix checks on incoming mail and rejects mail that is either from misconfigured relays or otherwise appears likely to be spam. Some of the specific requirements are:

Other advice to help mail reach its destination include:

If you still have trouble with email infrastructure at FreeBSD.org, send a note with the details to <postmaster@freebsd.org>; Include a date/time interval so that logs may be reviewed — and note that we only keep one week's worth of mail logs. (Be sure to specify the time zone or offset from UTC.)

While FreeBSD does not provide open access to any of their servers, others do provide open access UNIX® systems. The charge varies and limited services may be available.

Arbornet, Inc, also known as M-Net, has been providing open access to UNIX® systems since 1983. Starting on an Altos running System III, the site switched to BSD/OS in 1991. In June of 2000, the site switched again to FreeBSD. M-Net can be accessed via telnet and SSH and provides basic access to the entire FreeBSD software suite. However, network access is limited to members and patrons who donate to the system, which is run as a non-profit organization. M-Net also provides an bulletin board system and interactive chat.

He does not have one, and is just called “the BSD daemon”. If you insist upon using a name, call him “beastie”. Note that “beastie” is pronounced “BSD”.

More about the BSD daemon is available on his home page.

Perhaps. The BSD daemon is copyrighted by Marshall Kirk McKusick. Check his Statement on the Use of the BSD Daemon Figure for detailed usage terms.

In summary, the image can be used in a tasteful manner, for personal use, so long as appropriate credit is given. Before using the logo commercially, contact Kirk McKusick <mckusick@FreeBSD.org> for permission. More details are available on the BSD Daemon's home page.

Xfig and eps drawings are available under /usr/share/examples/BSD_daemon/.

Refer to the FreeBSD Glossary.

The really, really short answer is that you should not. The somewhat longer answer is that just because you are capable of building a bikeshed does not mean you should stop others from building one just because you do not like the color they plan to paint it. This is a metaphor indicating that you need not argue about every little feature just because you know enough to do so. Some people have commented that the amount of noise generated by a change is inversely proportional to the complexity of the change.

The longer and more complete answer is that after a very long argument about whether sleep(1) should take fractional second arguments, Poul-Henning Kamp <phk@FreeBSD.org> posted a long message entitled “A bike shed (any color will do) on greener grass...”. The appropriate portions of that message are quoted below.

Q. Has anyone done any temperature testing while running FreeBSD? I know Linux® runs cooler than DOS, but have never seen a mention of FreeBSD. It seems to run really hot.

A. No, but we have done numerous taste tests on blindfolded volunteers who have also had 250 micrograms of LSD-25 administered beforehand. 35% of the volunteers said that FreeBSD tasted sort of orange, whereas Linux® tasted like purple haze. Neither group mentioned any significant variances in temperature. We eventually had to throw the results of this survey out entirely anyway when we found that too many volunteers were wandering out of the room during the tests, thus skewing the results. We think most of the volunteers are at Apple now, working on their new “scratch and sniff” GUI. It is a funny old business we are in!

Seriously, FreeBSD uses the HLT (halt) instruction when the system is idle thus lowering its energy consumption and therefore the heat it generates. Also if you have ACPI (Advanced Configuration and Power Interface) configured, then FreeBSD can also put the CPU into a low power mode.

Q. Is there anything “odd” that FreeBSD does when compiling the kernel which would cause the memory to make a scratchy sound? When compiling (and for a brief moment after recognizing the floppy drive upon startup, as well), a strange scratchy sound emanates from what appears to be the memory banks.

A. Yes! You will see frequent references to “daemons” in the BSD documentation, and what most people do not know is that this refers to genuine, non-corporeal entities that now possess your computer. The scratchy sound coming from your memory is actually high-pitched whispering exchanged among the daemons as they best decide how to deal with various system administration tasks.

If the noise gets to you, a good fdisk /mbr from DOS will get rid of them, but do not be surprised if they react adversely and try to stop you. In fact, if at any point during the exercise you hear the satanic voice of Bill Gates coming from the built-in speaker, take off running and do not ever look back! Freed from the counterbalancing influence of the BSD daemons, the twin demons of DOS and Windows® are often able to re-assert total control over your machine to the eternal damnation of your soul. Now that you know, given a choice you would probably prefer to get used to the scratchy noises, no?

One thousand, one hundred and sixty-nine:

Twenty-three to complain to -CURRENT about the lights being out;

Four to claim that it is a configuration problem, and that such matters really belong on -questions;

Three to submit PRs about it, one of which is misfiled under doc and consists only of “it's dark”;

One to commit an untested lightbulb which breaks buildworld, then back it out five minutes later;

Eight to flame the PR originators for not including patches in their PRs;

Five to complain about buildworld being broken;

Thirty-one to answer that it works for them, and they must have updated at a bad time;

One to post a patch for a new lightbulb to -hackers;

One to complain that he had patches for this three years ago, but when he sent them to -CURRENT they were just ignored, and he has had bad experiences with the PR system; besides, the proposed new lightbulb is non-reflexive;

Thirty-seven to scream that lightbulbs do not belong in the base system, that committers have no right to do things like this without consulting the Community, and WHAT IS -CORE DOING ABOUT IT!?

Two hundred to complain about the color of the bicycle shed;

Three to point out that the patch breaks style(9);

Seventeen to complain that the proposed new lightbulb is under GPL;

Five hundred and eighty-six to engage in a flame war about the comparative advantages of the GPL, the BSD license, the MIT license, the NPL, and the personal hygiene of unnamed FSF founders;

Seven to move various portions of the thread to -chat and -advocacy;

One to commit the suggested lightbulb, even though it shines dimmer than the old one;

Two to back it out with a furious flame of a commit message, arguing that FreeBSD is better off in the dark than with a dim lightbulb;

Forty-six to argue vociferously about the backing out of the dim lightbulb and demanding a statement from -core;

Eleven to request a smaller lightbulb so it will fit their Tamagotchi if we ever decide to port FreeBSD to that platform;

Seventy-three to complain about the SNR on -hackers and -chat and unsubscribe in protest;

Thirteen to post “unsubscribe”, “How do I unsubscribe?”, or “Please remove me from the list”, followed by the usual footer;

One to commit a working lightbulb while everybody is too busy flaming everybody else to notice;

Thirty-one to point out that the new lightbulb would shine 0.364% brighter if compiled with TenDRA (although it will have to be reshaped into a cube), and that FreeBSD should therefore switch to TenDRA instead of GCC;

One to complain that the new lightbulb lacks fairings;

Nine (including the PR originators) to ask “what is MFC?”;

Fifty-seven to complain about the lights being out two weeks after the bulb has been changed.

Nik Clayton <nik@FreeBSD.org> adds:

I was laughing quite hard at this.

And then I thought, “Hang on, shouldn't there be '1 to document it.' in that list somewhere?”

And then I was enlightened :-)

Thomas Abthorpe <tabthorpe@FreeBSD.org> says: “None, real FreeBSD hackers are not afraid of the dark!”

It goes into a special data sink in the CPU where it is converted to heat which is vented through the heatsink / fan assembly. This is why CPU cooling is increasingly important; as people get used to faster processors, they become careless with their data and more and more of it ends up in /dev/null, overheating their CPUs. If you delete /dev/null (which effectively disables the CPU data sink) your CPU may run cooler but your system will quickly become constipated with all that excess data and start to behave erratically. If you have a fast network connection you can cool down your CPU by reading data out of /dev/random and sending it off somewhere; however you run the risk of overheating your network connection and / or angering your ISP, as most of the data will end up getting converted to heat by their equipment, but they generally have good cooling, so if you do not overdo it you should be OK.

Paul Robinson adds:

There are other methods. As every good sysadmin knows, it is part of standard practice to send data to the screen of interesting variety to keep all the pixies that make up your picture happy. Screen pixies (commonly mis-typed or re-named as “pixels”) are categorized by the type of hat they wear (red, green or blue) and will hide or appear (thereby showing the color of their hat) whenever they receive a little piece of food. Video cards turn data into pixie-food, and then send them to the pixies — the more expensive the card, the better the food, so the better behaved the pixies are. They also need constant stimulation — this is why screen savers exist.

To take your suggestions further, you could just throw the random data to console, thereby letting the pixies consume it. This causes no heat to be produced at all, keeps the pixies happy and gets rid of your data quite quickly, even if it does make things look a bit messy on your screen.

Incidentally, as an ex-admin of a large ISP who experienced many problems attempting to maintain a stable temperature in a server room, I would strongly discourage people sending the data they do not want out to the network. The fairies who do the packet switching and routing get annoyed by it as well.

Install games/sl and wait for her to mistype sl for ls.

See the FreeBSD Architecture Handbook.

Additionally, much general UNIX® knowledge is directly applicable to FreeBSD.

We accept all types of contributions: documentation, code, and even art. See the article on Contributing to FreeBSD for specific advice on how to do this.

And thanks for the thought!

There are currently 3 active/semi-active branches in the FreeBSD Subversion Repository. (Earlier branches are only changed very rarely, which is why there are only 3 active branches of development):

HEAD is not an actual branch tag. It is a symbolic constant for the current, non-branched development stream known as -CURRENT.

Right now, -CURRENT is the 13.X development stream; the 12-STABLE branch, stable/12/, forked off from -CURRENT in December 2018 and the 11-STABLE branch, stable/11/, forked off from -CURRENT in October 2016.

Here is typical kernel panic:

Fatal trap 12: page fault while in kernel mode
fault virtual address   = 0x40
fault code              = supervisor read, page not present
instruction pointer     = 0x8:0xf014a7e5
stack pointer           = 0x10:0xf4ed6f24
frame pointer           = 0x10:0xf4ed6f28
code segment            = base 0x0, limit 0xfffff, type 0x1b
                        = DPL 0, pres 1, def32 1, gran 1
processor eflags        = interrupt enabled, resume, IOPL = 0
current process         = 80 (mount)
interrupt mask          =
trap number             = 12
panic: page fault

This message is not enough. While the instruction pointer value is important, it is also configuration dependent as it varies depending on the kernel image. If it is a GENERIC kernel image from one of the snapshots, it is possible for somebody else to track down the offending function, but for a custom kernel, only you can tell us where the fault occurred.

To proceed:

However, the best way to track down the cause of a panic is by capturing a crash dump, then using kgdb(1) to generate a stack trace on the crash dump.

In any case, the method is this:

The make(1) process will have built two kernels. /usr/obj/usr/src/sys/MYKERNEL/kernel and /usr/obj/usr/src/sys/MYKERNEL/kernel.debug. kernel was installed as /boot/kernel/kernel, while kernel.debug can be used as the source of debugging symbols for kgdb(1).

To capture a crash dump, edit /etc/rc.conf and set dumpdev to point to either the swap partition or AUTO. This will cause the rc(8) scripts to use the dumpon(8) command to enable crash dumps. This command can also be run manually. After a panic, the crash dump can be recovered using savecore(8); if dumpdev is set in /etc/rc.conf, the rc(8) scripts will run savecore(8) automatically and put the crash dump in /var/crash.

Once the crash dump has been recovered , get a stack trace as follows:

% kgdb /usr/obj/usr/src/sys/MYKERNEL/kernel.debug /var/crash/vmcore.0
(kgdb) backtrace

Note that there may be several screens worth of information. Ideally, use script(1) to capture all of them. Using the unstripped kernel image with all the debug symbols should show the exact line of kernel source code where the panic occurred. The stack trace is usually read from the bottom up to trace the exact sequence of events that lead to the crash. kgdb(1) can also be used to print out the contents of various variables or structures to examine the system state at the time of the crash.

The ELF toolchain does not, by default, make the symbols defined in an executable visible to the dynamic linker. Consequently dlsym() searches on handles obtained from calls to dlopen(NULL, flags) will fail to find such symbols.

To search, using dlsym(), for symbols present in the main executable of a process, link the executable using the --export-dynamic option to the ELF linker (ld(1)).

By default, the kernel address space is 1 GB (2 GB for PAE) for i386. When running a network-intensive server or using ZFS, this will probably not be enough.

Add the following line to the kernel configuration file to increase available space and rebuild the kernel:

options KVA_PAGES=N

To find the correct value of N, divide the desired address space size (in megabytes) by four. (For example, it is 512 for 2 GB.)