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.de
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