1 Kernel Support for miscellaneous (your favourite) Binary Formats v1.1 2 ===================================================================== 3 4This Kernel feature allows you to invoke almost (for restrictions see below) 5every program by simply typing its name in the shell. 6This includes for example compiled Java(TM), Python or Emacs programs. 7 8To achieve this you must tell binfmt_misc which interpreter has to be invoked 9with which binary. Binfmt_misc recognises the binary-type by matching some bytes 10at the beginning of the file with a magic byte sequence (masking out specified 11bits) you have supplied. Binfmt_misc can also recognise a filename extension 12aka '.com' or '.exe'. 13 14To 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 16your needs) and echo it to /proc/sys/fs/binfmt_misc/register. 17Here 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 35There 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 41You may want to add the binary formats in one of your /etc/rc scripts during 42boot-up. Read the manual of your init program to figure out how to do this 43right. 44 45Think about the order of adding entries! Later added entries are matched first! 46 47 48A 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 60For java support see Documentation/java.txt 61 62 63You can enable/disable binfmt_misc or one binary type by echoing 0 (to disable) 64or 1 (to enable) to /proc/sys/fs/binfmt_misc/status or /proc/.../the_name. 65Catting the file tells you the current status of binfmt_misc/the entry. 66 67You can remove one entry or all entries by echoing -1 to /proc/.../the_name 68or /proc/sys/fs/binfmt_misc/status. 69 70 71HINTS: 72====== 73 74If you want to pass special arguments to your interpreter, you can 75write a wrapper script for it. See Documentation/java.txt for an 76example. 77 78Your interpreter should NOT look in the PATH for the filename; the 79kernel passes it the full filename to use. Using the PATH can cause 80unexpected behaviour and be a security hazard. 81 82 83There is a web page about binfmt_misc at 84http://www.tat.physik.uni-tuebingen.de/~rguenth/linux/binfmt_misc.html 85 86Richard G�nther <rguenth@tat.physik.uni-tuebingen.de> 87