Skip to main content. » The Guide | Manual pages | Mailing lists and Archives | CVS repository | Report orquery a bug | Software Packages Search L:http://ww w.N e NetBSD.org ww w.N etBSD.or Search Navigation: Home | About | Gallery | Download | Documentation | Support | Community | PortsNetBSD Documentation: Kernel Frequently Asked Kernel Questions yWhere to download the kernel source yHow to build a kernel yWhat exactly is a GENERIC k ernel? yWhat does mclpool limit reached: increase NMBCLUSTERS mean? yWhat does WARNING: SPL NOT LOWERED ON SYSCALL EXIT mean? yWhat does Stray interrupt on IRQ 7 mean? yWhy are kernels compiled with -msoft-float yKernel compiles on low memory machine seem very slow yProblems compiling a -current kernel yDebugging a kernel crash dump yGetting backtraces when debugging a kernel crash dump yWhat is DDB and what can I do in it?yGenerating a kernel crash dump yAdding a kernel to a boot floppy yI'm having trouble mounting the SCSI device for a new partition I've just created. What's up with this device-numbering scheme? Frequently Asked Hardware Questions yWhat does device not configured mean? yDebugging ATAPI or ATA (IDE) devices yDebugging USB devices yRecognising a new PnP device yRecognising a new PCMCIA device yIs PLIP (Parallel Line IP) supportedyWhat is UBC?Further reading
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NetBSD Documentation: Kernel
Frequently Asked Kernel Questions
y Where to download the kernel source
y How to build a kernel y What exactly is a GENERIC kernel?
y What does mclpool limit reached: increase NMBCLUSTERS mean? y What does WARNING: SPL NOT LOWERED ON SYSCALL EXIT mean?
y What does Stray interrupt on IRQ 7 mean? y Why are kernels compiled with -msoft-float
y K ernel compiles on low memory machine seem very slow y Problems compiling a -current kernel
y Debugging a kernel crash dump y Getting backtraces when debugging a kernel crash dump y What is DDB and what can I do in it? y Generating a kernel crash dump
y Adding a kernel to a boot floppy y I'm having trouble mounting the SCSI device for a new partition I've just created. What's
up with this device-numbering scheme?
Frequently Asked Hardware Questions
y What does device not configured mean? y Debugging ATAPI or ATA (IDE) devices
y Debugging USB devices y Recognising a new PnP device
y Recognising a new PCMCIA device y Is PLIP (Parallel Line IP) supported
y NetBSD specific documentation y Other online documentation
Frequently Asked Kernel Questions
Where to download the kernel source (top)
Official release source
To compile a custom kernel for the same release as you already have installed you only need the
kernel syssrc.tgz file. For a given release this is held in the gzipped tarfile'source/sets/syssrc.tgz' under the main directory for that release. For example NetBSD 3.1 kernelsource is in the file /pub/NetBSD/NetBSD-3.1/source/sets/syssrc.tgz.
If you have a NetBSD CD-Rom, the 'source/syssrc.tgz' file should be included. The source can be extracted anywhere, though the traditional location is inside /usr/src. To extract use "cd / ;
tar xvzpf <FILENAME> ".
'Bleeding edge' -current source, for the adventurous only!
The latest kernel sources are available from ftp.NetBSD.org or one of the mirrors in the directory/pub/NetBSD/NetBSD-current/src/sys/. To compile a kernel you should download the following
from /pub/NetBSD/NetBSD-current/tar_files/src:
y config.tar.gz (Source for the config(8) program)y sys.tar.gz (Complete kernel source for all architectures)
You should first build and install the 'config' program, in case it has changed since the versionyou are running. Since -current is on the active edge of NetBSD development, there can be
problems compiling a -current kernel. You are recommended to use source from an OfficialRelease until you are familiar with the configuration process.
Downloading the kernel source from a certain date
You might need to do this if you have installed a snapshot on your machine and need to rebuild
the kernel (and the -current kernel is too recent). Follow the directions on how to Track NetBSD-current with anoncvs.
How to build a kernel (top)
The procedure below applies only if you are compiling the kernel of the same version of NetBSD
that you have already installed. Updating to a newer kernel of the same major version should bealso fine using this procedure, but if you update a -current kernel, or want to update to a newer
major release, compiling a new toolchain first is required. Follow the description of building the
toolchain and new kernel with the build.sh script in the documentation about tracking -current:
y Updating an existing system (only the build.sh tools and build.sh kernel steps areneeded)
y Crosscompiling NetBSD with build.sh y Building the kernel using build.sh
The steps to build a kernel are:
1. Ensure you have installed the Compilers (comp.tgz) set that came with your base system.2. Download and extract the kernel source (see Where to download kernel source).
3. "cd /usr/src/sys/arch/<ARCH>/conf", where <ARCH> is your machine'sarchitecture such as 'i386', 'sparc', 'mac68k'.
4. "cp GENERIC <MYCONF>", where <MYCONF> is your name for this configuration. Youcould use your hostname, the machine type, or even your first name. K eep to letters,
numbers, and _ characters.5. Edit <MYCONF>. Initially you can skip this stage. You can remove drivers for CPU
types, hardware, and devices you do not have or use, or even enable options, such as on
i386 commenting out the 'pc0' line and enabling the 'vt0' to gain virtual consoles. A goodstart to determining what hardware drivers you definitely need to keep is to read the
output of "dmesg" or "dmesg | grep ' at '". For every line containing '<XXX> at
<YYY>' you need to keep the entries for both <XXX> and <YYY>. You should alsoread options(4) for information on the different kernel configuration options.
6. run ³config <MYCONF>´, which will generate the kernel build directory for <MYCONF>.
7. "cd ../compile/<MYCONF>" changes to the kernel build directory.
8. "make depend" generates a '.depend' file that enables the make program to see what
needs to be rebuilt (at this point it will be everything!).
9. "make" will compile the kernel. If all goes well you will be left with a 'netbsd' kernel.
This may take some significant time if you are on a VAX, some time on a big Alpha, andsomewhere in-between for the rest of us.
10. "mv /netbsd /netbsd.old ; mv
/usr/src/sys/arch/<ARCH>/compile/<MYCONF>/netbsd /" saves your current kernel,
(very important), and moves the new kernel ready to be booted.
11. "reboot" should reboot using your new kernel - the boot messages should contain a lineof the form: 'NetBSD <VERSION> (<MYCONF>) #0: <COMPILE_DATE>'
12. If you have any problems: You should boot your 'netbsd.old' kernel in single user mode.The procedure varies from port to port depending on the boot procedure, but on i386 it
would be:
a. Press SP ACE when the first NetBSD message appears
The term GENERIC refers to a kernel that is configured to run on just about any machinesupported by the machine architecture. The term originated from a line in the kernel
configuration file which specified that the root device was "generic" as well as a configuration
option. This option and that format of the configuration line is no longer used, but the name will probably stick for a while.
Since these kernels tend to include support for all the available device drivers and many modelsof machines that you are not using, you are encouraged to compile your own custom kernel.
What does mcl pool limit reached: increase NMBCLUSTER S mean? (top)
This means the kernel has run out of space to map mbuf clusters. mbuf clusters are used by the
network code to store packets and other network related data.
The default setting for NMBCLUSTERS is 1024 (256 in NetBSD 1.5 and earlier), so if you havethis problem, try doubling the value until the error message disappears. To display the current
value of NMBCLUSTERS you can use sysctl(8) as follows:
# sysctl kern.mbuf.nmbclusters
Alternatively, try
# echo 'print nmbclusters' | gdb -q /netbsd
See also options(4) for more details on kernel configuration options. To change the value, add
options NMBCLUSTERS=2048
to your kernel configuration, or patch the binary:
# gd b --write /net bsd (gdb) set nm bclusters=2048 (gdb) q uit
Note that if you patch the binary only, you will need to reboot for the change to take effect. If
you're on a platform which supports it, you can set the value with:
# sysctl -w kern.m buf.nm bclusters=2048
This will work, but will be lost on the next reboot. Combining this, and patching the binary,
would mean no need to build a new kernel or reboot.
What does W ARNING: SPL NOT LO W ERED ON SYSCALL EXIT mean? (top)
This kernel message means that there is a bug in the kernel where a syscall did "int x =
splfoo();" and did not call "splx(x);" before it returned. The splx(x); function in this
example would restore the system priority level to the one encoded in x, which was a value
previously returned by one of the other spl functions (in this case, the made up example of
splfoo();).
If you get this kernel message you should be dropped into ddb(4), the in-kernel debugger. Astack trace in ddb, accomplished by pushing 't', might show you the offending syscall(). It is
probably a good idea to send-pr(1) the output of the trace command (as well as any other relevant information), since you should under no circumstances be getting this kernel message.
See also spl(9) for more information on spl functions.
What does Stray interru pt on IRQ 7 mean? (top)
The "Stray interrupt on IRQ 7" kernel message means that the interrupt controller reported an
unmasked interrupt on IRQ 7, but no driver attached to that IRQ 'claimed' it.
There are two reasons this can happen:
1. In anything other than a PC, it would almost always means that there is a driver attached
to the IRQ (otherwise it would be masked), but it is the wrong driver.2. In a PC, there is the more obscure issue of 'default IR7's. That is, when a device asserts an
IRQ, but the IRQ is deasserted after the PIC latches the interrupt and before the CPUacknowledges it, the PIC just flat out lies about which IRQ it was.
There is a scheme for recognizing 'default IR7's, but it turns out that it fails badly on
some older systems, and in general it's better to fix drivers to not generate them in thefirst place. In some cases it's difficult to completely prevent them when using edge-
triggered interrupts though.
You should only get this kernel message running a kernel with the DEBUG option defined.
Why are kernels compiled with -msoft-float (top)
When a process makes a system call the kernel needs to save the processor state, so that it canlater switch back to the process. Floating point registers tend to be large and relatively plentiful,
making saving and restoring them an expensive operation. If the FPU is in the middle of an
operation the CPU will additionally be forced to sit and wait for it to finish before it can thencopy the registers.
Avoiding floating point registers in the kernel gives a significant performance win for systemcalls. Some processors, such as sparc, can also use lazy FP context switching to sometimes avoid
having to save and restore FP registers even when switching between processes.
On some architectures the compiler can use floating point registers to speed up certain operations(such as block memory copies), breaking the above, so '-msoft-float' is required.
Kernel compiles on low memory machine seem very slow (top)
By default NetBSD installs a GENERIC kernel which includes drivers for almost everysupported item of hardware, network protocol, and filesystem. While this allows one kernel torun on virtually every machine for a given port, it does result in it using more space than is really
needed, particularly on a small memory machine. This is compounded by kernel compiles usingthe -O2 optimisation level which tells the compiler to use extra memory and time to make the
kernel as fast as possible.
One option when building your own kernel is to use " make COPTS=-O" which instructs the
compiler to perform only the most effective optimisations. This will result in a fractionallyslower kernel, but it will take less time to compile.
If you are intending to take several 'compile and reboot into new kernel' passes whilecustomising a kernel on a low memory machine it may make sense to make the first few passes
using "make COPTS=-O", and then switch to "make" for the final pass.
Of course, generally the fastest way to compile a kernel on a low memory machine is to use
another machine, or temporarily add some more memory!
Problems compiling a -current kernel (top)
The first point to note is you should subscribe to the current-users mail list. Tracking -currentwithout reading current-users is akin to driving in the dark without any lights. You have been
warned :).
It is always worth downloading the latest config.tar.gz, compiling, installing and rerunning on
your config file - config changes reasonably frequently between releases.
Sometimes, binaries and/or libraries need to be updated before you will be able to build -currenton a release. In these situations, it may be simpler to install from a binary snapshot, and then
build -current. Snapshots of -current for i386 (for example) can be found in/pub/NetBSD/arch/i386/snapshot/. The src/UPDATING file contains information about these
important changes which you should be aware of when attempting to build -current, or a -currentkernel.
Debugging a kernel crash dump (top)
1. Ensure you have built a kernel from the same source with DEBUG, and 'makeoptions
DEBUG="-g"' enabled in the config file.
2. "gdb netbsd.gdb" (in kernel compile directory).
3. "target kvm /var/crash/netbsd.0.core" at the gdb prompt. Use "target kcore
This assumes you have "pseudo-device vnd" in your kernel config file, and a ready to usekernel.
I'm having trouble mounting the SCSI device for a new partition I've just created. What's
up with this device-numbering scheme? (top)
By default, SCSI devices under NetBSD are numbered starting from 0 in the order of SCSI ID
number. In other words, you lowest-numbered SCSI device will be /dev/sd0, the next device
will be /dev/sd1, etc. Notice that this is the assignment that they are given during the boot process.
If you compile your own kernels, you can set the SCSI devices to point to any SCSI ID number you want with a kernel configuration line like:
sd0 at scsibus0 target 4 lun 0sd* at scsibus? target ? lun ?
The above lines will make device sd0 point to the disk at SCSI ID#4 and the rest of the devices
will be assigned as described above. This is often referred to as "hardwiring" your SCSI devices,
and is recommended if you are using RAIDframe or ccd so as to avoid the device IDs beingchanged out from under the configuration if one device is powered off or broken.
Frequently Asked Hardware Questions
What does device not configured mean? (top)
y If this message appears during the autoconfiguration output of system boot, it means that
the kernel discovered a piece of hardware in your system that it doesn't have a devicedriver for. This means that either the device driver exists and has not been compiled into
the kernel you booted, or the device driver doesn't exist at all (in which case, it's time tocontact a friendly developer and offer him testing hardware in exchange for writing a
device driver).
Since GENERIC kernels are used for basic installation, it is important that they be stableand known to work; as such, device drivers that are not yet stable are not compiled into
GENERIC kernels by default. Examination of a GENERIC kernel configuration file for your system may reveal experimental device drivers for your device which are"commented out." If you compile a kernel of your own (please don't call it GENERIC),
y If this message appears when you try to access a device node in /dev (e.g. a SCSI disk),this means that the driver can't find the specific device unit you tried to access, e.g.
accessing a SCSI disk that isn't there, or the driver is not compiled in the kernel.
Often, this happens when the device nodes in /etc/fstab don't match what the kernel
found during autoconfiguration at boot time, and the "mount" command in /etc/rc triesto mount all the filesystems. You should double check that the devices you're trying to
use were actually found by the kernel at boot time, by examining /var/run/dmesg.boot
(a saved copy of the boot time autoconfiguration output).
Another case where this can happen is when a certain kernel subsystem which is
implemented as a pseudo-device is not compiled into the kernel or loaded as an LK M and
a configuration program wants to configure it using a device node in /dev. For example
when a firewall is not compiled into the kernel or loaded as an LK M and the pfctl(8) or ipf(8) utility attempts to load firewall rules. If such utility does not print a helpful
message indicating what device it tried to use, ktrace(1) can help you find what's going
on inside a command, and to determine you what's being accessed that may cause theerror message.
And it can happen in many other cases when a nonexistent device or device without a
driver is accessed, like when a nonexistent network interface name is passed toifconfig(8) (in this case, if you are sure that you have the right driver, maybe the interface
must be explicitly created by a command like ifconfig vlan0 create ² this is truefor most of the network pseudo-devices like sl(4), vlan(4) or stf(4)).
Debugging ATAPI or ATA (IDE) devices (top)
If a kernel is compiled with WDCDEBUG defined, then gdb can be used to patchwdcdebug_atapi_mask and wdcdebug_mask. Setting the appropriate bits in these variables willcause the kernel to output verbose information about ATAPI and ATA operations. (Currently
NetBSD defaults to WDCDEBUG enabled.)
For the maximum level of output, use:
# gd b --write /net bsd (gdb) set wdcde bug_atapi_mask=0xff (gdb) set wdcde bug_mask=0xff (gdb) q uit
Note: This will produce an extremely large quantity of output. To select individual options, look for the list of bitflags directly above:
y wdcdebug_atapi_mask in /usr/src/sys/dev/scsipi/atapi_wdc.c
If you have problems with USB devices, you can enable verbose messages in the usb driver:
y Compile a kernel with USB_DEBUG and DDB defined.
y Boot with -d to enter ddb(4).
y In ddb set the variables usbdebug and uhcidebug to 5 ("write usbdebug 5" and "write
uhcidebug 5")y Plug something in and type continue.
R ecognising a new PnP device (top)
This assumes the device is of a generic type which is already supported, but the device ID is notrecognised. Adding a device that performs differently includes writing code.
1. It should be reported in the boot messages as 'not configured'. Note the device ID (in
this case USR3031):
isapnp0: <U.S. Ro
botics 56K FAX INT, U
S
R3031, , > port 0x3e8/8irq 5not configured
2. Add an appropriate entry to /usr/src/sys/dev/isapnp/isapnpdevs:
devlogic com USR3031 USR 56k Faxmodem
3. Regenerate isapnpdevs.{c,h} using 'make -f Makefile.isapnpdevs'.
4. Rebuild the kernel 5. Submit a PR with the changes, via send-pr(1) or the online form.
R ecognising a new PCMCIA device (top)
This assumes the device is of a generic type which is already supported, but the device ID is notrecognised. Adding a device that performs differently includes writing code.
1. Compile a kernel with options(4) PCMCIAVERBOSE.
2. Check the boot messages - the card should be reported as 'not configured'. Note the
Manufacturer and product codes (in this case 0x143 and 0x201):3. pcmcia0: CIS version PCMCIA 2.0 or 2.14. pcmcia0: CIS info: Grey Cell, GCS2000, Gold II, 15. pcmcia0: Manufacturer code 0x143, product 0x201 6. pcmcia0: function 0: network adapter, ccr addr 3f8 mask 17.
Add vendor and product entries to /usr/src/sys/dev/pcmcia/pcmciadevs
8. Regenerate pcmciadevs.h and pcmciadevs_data.h using 'make -f
Makefile.pcmciadevs'.9. Add an entry to the device table at the top of the appropriate bus attach file in
/usr/src/sys/dev/pcmcia/, for example an ne2000 compatible card would use/usr/src/sys/dev/pcmcia/if_ne_pcmcia.c
10. Rebuild the kernel
11. Submit a PR with the changes, via send-pr(1) or the online form.
There are patches from Martin Husemann which add PLIP support to NetBSD/i386, submitted asPR 1278. The patches at the end of the PR should apply to the NetBSD 1.3.3 source tree.
What is UBC? (top)
UBC stands for the Unified Buffer Cache project. It was written by Chuck Silvers, and has beenintegrated into NetBSD since 1.5L (Nov 2000). When upgrading from a non-UBC setup, you'll
need to rerun config(8) again, but before you do, you'll want to remove any settings for "BUFCACHE", "NBUF" or "BUFPAGES", and let the size of the buffer cache go back to the
default. Under UBC, the traditional buffer cache is no longer used for storing regular file data,only metadata, so you want to allow the VM system to manage most of your physical memory.
The default buffer cache size will be fine for most people, regardless of the amount of memory inthe machine. The amount of memory in the boot messages about "using X buffers containing Y
memory" no longer indicates the amount of memory available for caching file data, so don't
worry if those numbers don't change.
The important difference is that more memory will be available for caching regular file data, so
filesystem i/o will be faster since there will be more times when the data you're accessing isalready in memory. How much faster depends on what you're doing, but you'll probably notice
the difference.
See also: UBC: An Efficient Unified I/O and Memory Caching Subsystem for NetBSD by Chuck Silvers.
Further reading
NetBSD specific documentation (top)
y K ernel programming FAQ y Writing a pseudo-device driver
y K ernel Profiling HOWTO y Vendor-specific ELF Note Elements
y UVM, the new Virtual Memory system y Why implement traditional vfork()
y Debugging the NetBSD kernel with GDB HO
WTO
y Information about non-executable mappings
y NetBSD Internals
Other online documentation (top)
y Porting BSD UNIX to a New Platform
y Chapter 9 (NFS) from Design and Implementation of 4.4BSD
