Command Section
KVM(3)                 FreeBSD Library Functions Manual                 KVM(3)

     kvm - kernel memory interface

     Kernel Data Access Library (libkvm, -lkvm)

     The kvm library provides a uniform interface for accessing kernel virtual
     memory images, including live systems and crash dumps.  Access to live
     systems is via sysctl(3) for some functions, and mem(4) and kmem(4) for
     other functions, while crash dumps can be examined via the core file
     generated by savecore(8).  The interface behaves similarly in both cases.
     Memory can be read and written, kernel symbol addresses can be looked up
     efficiently, and information about user processes can be gathered.

     The kvm_open() function is first called to obtain a descriptor for all
     subsequent calls.

     The kvm interface was first introduced in SunOS.  A considerable number
     of programs have been developed that use this interface, making backward
     compatibility highly desirable.  In most respects, the Sun kvm interface
     is consistent and clean.  Accordingly, the generic portion of the
     interface (i.e., kvm_open(), kvm_close(), kvm_read(), kvm_write(), and
     kvm_nlist()) has been incorporated into the BSD interface.  Indeed, many
     kvm applications (i.e., debuggers and statistical monitors) use only this
     subset of the interface.

     The process interface was not kept.  This is not a portability issue
     since any code that manipulates processes is inherently machine

     Finally, the Sun kvm error reporting semantics are poorly defined.  The
     library can be configured either to print errors to stderr automatically,
     or to print no error messages at all.  In the latter case, the nature of
     the error cannot be determined.  To overcome this, the BSD interface
     includes a routine, kvm_geterr(3), to return (not print out) the error
     message corresponding to the most recent error condition on the given

     The kvm library supports inspection of crash dumps from non-native
     kernels.  Only a limited subset of the kvm interface is supported for
     these dumps.  To inspect a crash dump of a non-native kernel, the caller
     must provide a resolver function when opening a descriptor via
     kvm_open2().  In addition, the kvm interface defines an integer type
     (kvaddr_t) that is large enough to hold all valid addresses of all
     supported architectures.  The interface also defines a new namelist
     structure type (struct kvm_nlist) for use with kvm_nlist2().  To avoid
     address truncation issues, the caller should use kvm_nlist2() and
     kvm_read2() in place of kvm_nlist() and kvm_read(), respectively.
     Finally, only a limited subset of operations are supported for non-native
     crash dumps: kvm_close(), kvm_geterr() kvm_open2(), kvm_native(),
     kvm_nlist2(), and kvm_read2().

     kvm_close(3), kvm_getargv(3), kvm_getenvv(3), kvm_geterr(3),
     kvm_getloadavg(3), kvm_getprocs(3), kvm_getswapinfo(3), kvm_native(3),
     kvm_nlist(3), kvm_nlist2(3), kvm_open(3), kvm_open2(3), kvm_openfiles(3),
     kvm_read(3), kvm_read2(3), kvm_write(3), sysctl(3), kmem(4), mem(4)

FreeBSD 11.1-RELEASE-p4         April 30, 2016         FreeBSD 11.1-RELEASE-p4
Command Section