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]

     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 when-
     ever 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 data-
     base 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.

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

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

     --admindir directory
           Specifies the administrative directory, when this is to be differ-
           ent 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

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

           Display some usage information.

           You cannot install a format with any of the names ".", "..", "reg-
           ister", 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

     --display [name]
           Display any information held in the database about the binary for-
           mat 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 match-
           ing 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.

     --magic byte-sequence
           This matches all files with the magic number byte-sequence.  Hexa-
           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".  Hexadeci-
           mal escapes are not recognized here.  Extension matching is case-

     --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 han-
           dled 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.

     A format file is a sequence of options, one per line, corresponding
     roughly to the options given to an --install command.  Each option con-
     sists 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, and
     credentials options correspond to the command-line options of the same

     0     The requested action was successfully performed.

     2     Problems were encountered whilst parsing the command line or per-
           forming the action.

     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'


     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.

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

Debian                         January 24, 2011                         Debian
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