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binfmt vmisc

Guest on 31st July 2022 05:22:16 PM

  1.      Kernel Support for miscellaneous (your favourite) Binary Formats v1.1
  2.      =====================================================================
  3.  
  4. This Kernel feature allows you to invoke almost (for restrictions see below)
  5. every program by simply typing its name in the shell.
  6. This includes for example compiled Java(TM), Python or Emacs programs.
  7.  
  8. To achieve this you must tell binfmt_misc which interpreter has to be invoked
  9. with which binary. Binfmt_misc recognises the binary-type by matching some bytes
  10. at the beginning of the file with a magic byte sequence (masking out specified
  11. bits) you have supplied. Binfmt_misc can also recognise a filename extension
  12. aka '.com' or '.exe'.
  13.  
  14. To actually register a new binary type, you have to set up a string looking like
  15. :name:type:offset:magic:mask:interpreter: (where you can choose the ':' upon
  16. your needs) and echo it to /proc/sys/fs/binfmt_misc/register.
  17. Here is what the fields mean:
  18.  - 'name' is an identifier string. A new /proc file will be created with this
  19.    name below /proc/sys/fs/binfmt_misc
  20.  - 'type' is the type of recognition. Give 'M' for magic and 'E' for extension.
  21.  - 'offset' is the offset of the magic/mask in the file, counted in bytes. This
  22.    defaults to 0 if you omit it (i.e. you write ':name:type::magic...')
  23.  - 'magic' is the byte sequence binfmt_misc is matching for. The magic string
  24.    may contain hex-encoded characters like \x0a or \xA4. In a shell environment
  25.    you will have to write \\x0a to prevent the shell from eating your \.
  26.    If you chose filename extension matching, this is the extension to be
  27.    recognised (without the '.', the \x0a specials are not allowed). Extension
  28.    matching is case sensitive!
  29.  - 'mask' is an (optional, defaults to all 0xff) mask. You can mask out some
  30.    bits from matching by supplying a string like magic and as long as magic.
  31.    The mask is anded with the byte sequence of the file.
  32.  - 'interpreter' is the program that should be invoked with the binary as first
  33.    argument (specify the full path)
  34.  
  35. There are some restrictions:
  36.  - the whole register string may not exceed 255 characters
  37.  - the magic must reside in the first 128 bytes of the file, i.e.
  38.    offset+size(magic) has to be less than 128
  39.  - the interpreter string may not exceed 127 characters
  40.  
  41. You may want to add the binary formats in one of your /etc/rc scripts during
  42. boot-up. Read the manual of your init program to figure out how to do this
  43. right.
  44.  
  45. Think about the order of adding entries! Later added entries are matched first!
  46.  
  47.  
  48. A few examples (assumed you are in /proc/sys/fs/binfmt_misc):
  49.  
  50. - enable support for em86 (like binfmt_em86, for Alpha AXP only):
  51.   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
  52.   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
  53.  
  54. - enable support for packed DOS applications (pre-configured dosemu hdimages):
  55.   echo ':DEXE:M::\x0eDEX::/usr/bin/dosexec:' > register
  56.  
  57. - enable support for Windows executables using wine:
  58.   echo ':DOSWin:M::MZ::/usr/local/bin/wine:' > register
  59.  
  60. For java support see Documentation/java.txt
  61.  
  62.  
  63. You can enable/disable binfmt_misc or one binary type by echoing 0 (to disable)
  64. or 1 (to enable) to /proc/sys/fs/binfmt_misc/status or /proc/.../the_name.
  65. Catting the file tells you the current status of binfmt_misc/the entry.
  66.  
  67. You can remove one entry or all entries by echoing -1 to /proc/.../the_name
  68. or /proc/sys/fs/binfmt_misc/status.
  69.  
  70.  
  71. HINTS:
  72. ======
  73.  
  74. If you want to pass special arguments to your interpreter, you can
  75. write a wrapper script for it. See Documentation/java.txt for an
  76. example.
  77.  
  78. Your interpreter should NOT look in the PATH for the filename; the
  79. kernel passes it the full filename to use.  Using the PATH can cause
  80. unexpected behaviour and be a security hazard.
  81.  
  82.  
  83. There is a web page about binfmt_misc at
  84. http://www.anatom.uni-tuebingen.de/~richi/linux/binfmt_misc.html
  85.  
  86. Richard Günther, richard.guenther@student.uni-tuebingen.d

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