Provided by: binfmt-support_2.1.8-2_amd64 bug

NAME

       update-binfmts — maintain registry of executable binary formats

SYNOPSIS

       update-binfmts [options] --install name path spec
       update-binfmts [options] --remove name path
       update-binfmts [options] --import [name]
       update-binfmts [options] --display [name]
       update-binfmts [options] --enable [name]
       update-binfmts [options] --disable [name]
       update-binfmts [options] --find [path]

DESCRIPTION

       Versions  2.1.43  and  later  of  the Linux kernel have contained the binfmt_misc module.  This enables a
       system administrator to register interpreters for various binary formats based on a magic number or their
       file extension, and cause the appropriate interpreter to be invoked whenever a matching file is executed.
       Think of it as a more flexible version of the #! executable interpreter mechanism, or as something  which
       can  behave  a  little  like  "associations"  in certain other operating systems (though in GNU/Linux the
       tendency is to keep this sort of thing somewhere else, like your file manager).  update-binfmts manages a
       persistent database of these interpreters.

       When each package providing a registered interpreter is installed, changed, or removed, update-binfmts is
       called to update information about that interpreter.  update-binfmts is usually called from the  postinst
       or prerm scripts in Debian packages.

OPTIONS

       Exactly one action must be specified; this may be accompanied by any one of the common options.

   COMMON OPTIONS
       --package package-name
             Specifies  the name of the current package, to be used by package post-installation and pre-removal
             scripts.  System administrators installing binary formats for local use should probably ignore this
             option.

             When installing new formats, the --import action should be used instead.

       --admindir directory
             Specifies the administrative  directory,  when  this  is  to  be  different  from  the  default  of
             /var/lib/binfmts.

       --importdir directory
             Specifies  the  directory  from  which  packaged  binary  formats  are imported, when this is to be
             different from the default of /usr/share/binfmts.

       --test
             Don't do anything, just demonstrate what would be done.

       --help
             Display some usage information.

       --version
             Display version information.

   ACTIONS
       --install name path spec
             Install a binary format identified  by  name  with  interpreter  path  into  the  database.   After
             registration,  this  format will be used when the kernel tries to execute a file matching spec (see
             “BINARY FORMAT SPECIFICATIONS” below).

             --install will attempt to enable this binary format in the kernel as well as adding it to  its  own
             database; see --enable below.

             You  cannot install a format with any of the names ".", "..", "register", or "status", as these are
             used by the filesystem or the binfmt_misc module.

       --remove name path
             Remove the binary format identified by name with interpreter path from  the  database.   This  will
             also attempt to disable the binary format in the kernel; see --disable below.

       --import [name]
             Import a packaged format file called name, or import all format files currently on the system if no
             name  is  given.   If  name  is not a full path, it is assumed to be a file in the import directory
             (/usr/share/binfmts by default).  See “FORMAT FILES” below  for  the  required  contents  of  these
             files.

             For  packages,  this is preferable to using the --install option, as a format file can be installed
             without update-binfmts needing to be available.

       --display [name]
             Display any information held in the database about the binary format identifier name, or about  all
             known  binary  formats if no name is given.  Also show whether displayed binary formats are enabled
             or disabled.

       --enable [name]
             Enable binary format name, or all known binary formats if no name is given,  in  the  kernel,  thus
             enabling direct execution of matching files.  You must have binfmt_misc compiled into the kernel or
             loaded as a module for this to work.

       --disable [name]
             Disable  binary  format  name, or all known binary formats if no name is given, in the kernel, thus
             disabling direct execution of matching files.  You must have binfmt_misc compiled into  the  kernel
             or loaded as a module for this to work.

       --find [path]
             Print  the list of interpreters that will be tried in sequence when attempting to execute path, one
             per line.  The first one for which execvp(3) succeeds will be used.

             Note that if multiple formats match an executable, then the order is in general  not  defined,  and
             may  not be preserved between update-binfmts operations, so you should generally try to ensure that
             this option prints at most one line for any given path.  The exception to this is that  any  format
             with a userspace detector will be run before any format without a userspace detector.

   BINARY FORMAT SPECIFICATIONS
       --magic byte-sequence
             This matches all files with the magic number byte-sequence.  Hexadecimal escapes may be included in
             the  byte-sequence  by  preceding  them  with  \x,  for example ‘\x0a’ for a linefeed.  Remember to
             protect such escapes with quotes or an additional backslash to prevent their interpretation by  the
             shell.

             Also see --offset and --mask.

       --offset offset
             This  is the offset of the magic/mask in the file, counted in bytes.  The default is 0.  Only valid
             with --magic.

       --mask byte-sequence
             This mask will be logically-ANDed with the string to be checked against the magic number given with
             --magic.  The default is all 0xff, i.e. no effect.  Only valid with --magic.

       --extension extension
             This matches all files whose names end in ".extension".  Hexadecimal  escapes  are  not  recognized
             here.  Extension matching is case-sensitive.

       --detector path
             If  this  option  is  used,  a userspace detector program will be used to check whether the file is
             suitable for this interpreter.  This may be used when the binary format is more complex than can be
             handled by the kernel's format specifications alone.  The program should return  an  exit  code  of
             zero if the file is appropriate and non-zero otherwise.

       --credentials yes, --credentials no
             Whether  to  keep  the credentials of the original binary to run the interpreter; this is typically
             useful to run setuid binaries, but has security implications.

       --preserve yes, --preserve no
             Whether to preserve the original argv[0] when running the interpreter, rather than  overwriting  it
             with the full path to the binary.

       --fix-binary yes, --fix-binary no
             Whether  to  open  the interpreter binary immediately and always use the opened image.  This allows
             the interpreter from the host to be  used  regardless  of  usage  in  chroots  or  different  mount
             namespaces.   The  default  behaviour  is  no,  meaning that the kernel should open the interpreter
             binary lazily when needed.  This option requires Linux 4.8 or newer.

   FORMAT FILES
       A format file is a sequence of options, one per line, corresponding roughly to the options  given  to  an
       --install command.  Each option consists of a key, followed by whitespace, followed by a value.

       The  package  option  should  be set to the current package.  The interpreter option should be set to the
       path to the interpreter that will handle  this  binary  format.   The  magic,  offset,  mask,  extension,
       detector,  credentials,  preserve,  and  fix-binary options correspond to the command-line options of the
       same names.

EXIT STATUS

       0     The requested action was successfully performed.

       2     Problems were encountered whilst parsing the command line or performing the action.

EXAMPLES

       This format file can be used with an interpreter capable of handling Java .class files:

           package javawrapper
           interpreter /usr/bin/javawrapper
           magic \xca\xfe\xba\xbe

       This corresponds roughly to the following command:

           update-binfmts --package javawrapper \
               --install javawrapper /usr/bin/javawrapper \
               --magic '\xca\xfe\xba\xbe'

NOTES

       If you're not careful, you can break your system with update-binfmts.  An easy  way  to  do  this  is  to
       register  an  ELF  binary  as  a  handler  for ELF, which will almost certainly cause your system to hang
       immediately; even if it doesn't, you won't be able to run  update-binfmts  to  fix  it.   In  the  future
       update-binfmts  may  have  some  checks  to  prevent this sort of thing happening accidentally, though of
       course you can still manipulate the binfmt_misc kernel module directly.

AUTHOR

       update-binfmts is copyright (C) 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008,  2009,  2010,  2011
       Colin  Watson  <cjwatson@debian.org>.   See the GNU General Public License version 3 or later for copying
       conditions.

       You can find the GNU GPL v3 in /usr/share/common-licenses/GPL-3 on any modern Debian system.

       Richard Guenther wrote the binfmt_misc kernel module.

THANKS

       Ian Jackson wrote update-alternatives and dpkg-divert, from which this program borrows heavily.

Debian                                          January 24, 2011                               UPDATE-BINFMTS(8)