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- Kernel Support for miscellaneous (your favourite) Binary Formats v1.1
- =====================================================================
-
-This Kernel feature allows you to invoke almost (for restrictions see below)
-every program by simply typing its name in the shell.
-This includes for example compiled Java(TM), Python or Emacs programs.
-
-To achieve this you must tell binfmt_misc which interpreter has to be invoked
-with which binary. Binfmt_misc recognises the binary-type by matching some bytes
-at the beginning of the file with a magic byte sequence (masking out specified
-bits) you have supplied. Binfmt_misc can also recognise a filename extension
-aka '.com' or '.exe'.
-
-First you must mount binfmt_misc:
- mount binfmt_misc -t binfmt_misc /proc/sys/fs/binfmt_misc
-
-To actually register a new binary type, you have to set up a string looking like
-:name:type:offset:magic:mask:interpreter:flags (where you can choose the ':' upon
-your needs) and echo it to /proc/sys/fs/binfmt_misc/register.
-Here is what the fields mean:
- - 'name' is an identifier string. A new /proc file will be created with this
- name below /proc/sys/fs/binfmt_misc
- - 'type' is the type of recognition. Give 'M' for magic and 'E' for extension.
- - 'offset' is the offset of the magic/mask in the file, counted in bytes. This
- defaults to 0 if you omit it (i.e. you write ':name:type::magic...')
- - 'magic' is the byte sequence binfmt_misc is matching for. The magic string
- may contain hex-encoded characters like \x0a or \xA4. In a shell environment
- you will have to write \\x0a to prevent the shell from eating your \.
- If you chose filename extension matching, this is the extension to be
- recognised (without the '.', the \x0a specials are not allowed). Extension
- matching is case sensitive!
- - 'mask' is an (optional, defaults to all 0xff) mask. You can mask out some
- bits from matching by supplying a string like magic and as long as magic.
- The mask is anded with the byte sequence of the file.
- - 'interpreter' is the program that should be invoked with the binary as first
- argument (specify the full path)
- - 'flags' is an optional field that controls several aspects of the invocation
- of the interpreter. It is a string of capital letters, each controls a certain
- aspect. The following flags are supported -
- 'P' - preserve-argv[0]. Legacy behavior of binfmt_misc is to overwrite the
- original argv[0] with the full path to the binary. When this flag is
- included, binfmt_misc will add an argument to the argument vector for
- this purpose, thus preserving the original argv[0].
- 'O' - open-binary. Legacy behavior of binfmt_misc is to pass the full path
- of the binary to the interpreter as an argument. When this flag is
- included, binfmt_misc will open the file for reading and pass its
- descriptor as an argument, instead of the full path, thus allowing
- the interpreter to execute non-readable binaries. This feature should
- be used with care - the interpreter has to be trusted not to emit
- the contents of the non-readable binary.
- 'C' - credentials. Currently, the behavior of binfmt_misc is to calculate
- the credentials and security token of the new process according to
- the interpreter. When this flag is included, these attributes are
- calculated according to the binary. It also implies the 'O' flag.
- This feature should be used with care as the interpreter
- will run with root permissions when a setuid binary owned by root
- is run with binfmt_misc.
-
-
-There are some restrictions:
- - the whole register string may not exceed 255 characters
- - the magic must reside in the first 128 bytes of the file, i.e.
- offset+size(magic) has to be less than 128
- - the interpreter string may not exceed 127 characters
-
-To use binfmt_misc you have to mount it first. You can mount it with
-"mount -t binfmt_misc none /proc/sys/fs/binfmt_misc" command, or you can add
-a line "none /proc/sys/fs/binfmt_misc binfmt_misc defaults 0 0" to your
-/etc/fstab so it auto mounts on boot.
-
-You may want to add the binary formats in one of your /etc/rc scripts during
-boot-up. Read the manual of your init program to figure out how to do this
-right.
-
-Think about the order of adding entries! Later added entries are matched first!
-
-
-A few examples (assumed you are in /proc/sys/fs/binfmt_misc):
-
-- enable support for em86 (like binfmt_em86, for Alpha AXP only):
- echo ':i386:M::\x7fELF\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x03:\xff\xff\xff\xff\xff\xfe\xfe\xff\xff\xff\xff\xff\xff\xff\xff\xff\xfb\xff\xff:/bin/em86:' > register
- echo ':i486:M::\x7fELF\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x06:\xff\xff\xff\xff\xff\xfe\xfe\xff\xff\xff\xff\xff\xff\xff\xff\xff\xfb\xff\xff:/bin/em86:' > register
-
-- enable support for packed DOS applications (pre-configured dosemu hdimages):
- echo ':DEXE:M::\x0eDEX::/usr/bin/dosexec:' > register
-
-- enable support for Windows executables using wine:
- echo ':DOSWin:M::MZ::/usr/local/bin/wine:' > register
-
-For java support see Documentation/java.txt
-
-
-You can enable/disable binfmt_misc or one binary type by echoing 0 (to disable)
-or 1 (to enable) to /proc/sys/fs/binfmt_misc/status or /proc/.../the_name.
-Catting the file tells you the current status of binfmt_misc/the entry.
-
-You can remove one entry or all entries by echoing -1 to /proc/.../the_name
-or /proc/sys/fs/binfmt_misc/status.
-
-
-HINTS:
-======
-
-If you want to pass special arguments to your interpreter, you can
-write a wrapper script for it. See Documentation/java.txt for an
-example.
-
-Your interpreter should NOT look in the PATH for the filename; the kernel
-passes it the full filename (or the file descriptor) to use. Using $PATH can
-cause unexpected behaviour and can be a security hazard.
-
-
-There is a web page about binfmt_misc at
-http://www.tat.physik.uni-tuebingen.de
-
-Richard G√ľnther <rguenth@tat.physik.uni-tuebingen.de>