diff options
author | Linus Torvalds <torvalds@ppc970.osdl.org> | 2005-04-16 18:20:36 -0400 |
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committer | Linus Torvalds <torvalds@ppc970.osdl.org> | 2005-04-16 18:20:36 -0400 |
commit | 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (patch) | |
tree | 0bba044c4ce775e45a88a51686b5d9f90697ea9d /Documentation/binfmt_misc.txt |
Linux-2.6.12-rc2v2.6.12-rc2
Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.
Let it rip!
Diffstat (limited to 'Documentation/binfmt_misc.txt')
-rw-r--r-- | Documentation/binfmt_misc.txt | 116 |
1 files changed, 116 insertions, 0 deletions
diff --git a/Documentation/binfmt_misc.txt b/Documentation/binfmt_misc.txt new file mode 100644 index 000000000000..d097f09ee15a --- /dev/null +++ b/Documentation/binfmt_misc.txt | |||
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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 | First you must mount binfmt_misc: | ||
15 | mount binfmt_misc -t binfmt_misc /proc/sys/fs/binfmt_misc | ||
16 | |||
17 | To actually register a new binary type, you have to set up a string looking like | ||
18 | :name:type:offset:magic:mask:interpreter:flags (where you can choose the ':' upon | ||
19 | your needs) and echo it to /proc/sys/fs/binfmt_misc/register. | ||
20 | Here is what the fields mean: | ||
21 | - 'name' is an identifier string. A new /proc file will be created with this | ||
22 | name below /proc/sys/fs/binfmt_misc | ||
23 | - 'type' is the type of recognition. Give 'M' for magic and 'E' for extension. | ||
24 | - 'offset' is the offset of the magic/mask in the file, counted in bytes. This | ||
25 | defaults to 0 if you omit it (i.e. you write ':name:type::magic...') | ||
26 | - 'magic' is the byte sequence binfmt_misc is matching for. The magic string | ||
27 | may contain hex-encoded characters like \x0a or \xA4. In a shell environment | ||
28 | you will have to write \\x0a to prevent the shell from eating your \. | ||
29 | If you chose filename extension matching, this is the extension to be | ||
30 | recognised (without the '.', the \x0a specials are not allowed). Extension | ||
31 | matching is case sensitive! | ||
32 | - 'mask' is an (optional, defaults to all 0xff) mask. You can mask out some | ||
33 | bits from matching by supplying a string like magic and as long as magic. | ||
34 | The mask is anded with the byte sequence of the file. | ||
35 | - 'interpreter' is the program that should be invoked with the binary as first | ||
36 | argument (specify the full path) | ||
37 | - 'flags' is an optional field that controls several aspects of the invocation | ||
38 | of the interpreter. It is a string of capital letters, each controls a certain | ||
39 | aspect. The following flags are supported - | ||
40 | 'P' - preserve-argv[0]. Legacy behavior of binfmt_misc is to overwrite the | ||
41 | original argv[0] with the full path to the binary. When this flag is | ||
42 | included, binfmt_misc will add an argument to the argument vector for | ||
43 | this purpose, thus preserving the original argv[0]. | ||
44 | 'O' - open-binary. Legacy behavior of binfmt_misc is to pass the full path | ||
45 | of the binary to the interpreter as an argument. When this flag is | ||
46 | included, binfmt_misc will open the file for reading and pass its | ||
47 | descriptor as an argument, instead of the full path, thus allowing | ||
48 | the interpreter to execute non-readable binaries. This feature should | ||
49 | be used with care - the interpreter has to be trusted not to emit | ||
50 | the contents of the non-readable binary. | ||
51 | 'C' - credentials. Currently, the behavior of binfmt_misc is to calculate | ||
52 | the credentials and security token of the new process according to | ||
53 | the interpreter. When this flag is included, these attributes are | ||
54 | calculated according to the binary. It also implies the 'O' flag. | ||
55 | This feature should be used with care as the interpreter | ||
56 | will run with root permissions when a setuid binary owned by root | ||
57 | is run with binfmt_misc. | ||
58 | |||
59 | |||
60 | There are some restrictions: | ||
61 | - the whole register string may not exceed 255 characters | ||
62 | - the magic must reside in the first 128 bytes of the file, i.e. | ||
63 | offset+size(magic) has to be less than 128 | ||
64 | - the interpreter string may not exceed 127 characters | ||
65 | |||
66 | To use binfmt_misc you have to mount it first. You can mount it with | ||
67 | "mount -t binfmt_misc none /proc/sys/fs/binfmt_misc" command, or you can add | ||
68 | a line "none /proc/sys/fs/binfmt_misc binfmt_misc defaults 0 0" to your | ||
69 | /etc/fstab so it auto mounts on boot. | ||
70 | |||
71 | You may want to add the binary formats in one of your /etc/rc scripts during | ||
72 | boot-up. Read the manual of your init program to figure out how to do this | ||
73 | right. | ||
74 | |||
75 | Think about the order of adding entries! Later added entries are matched first! | ||
76 | |||
77 | |||
78 | A few examples (assumed you are in /proc/sys/fs/binfmt_misc): | ||
79 | |||
80 | - enable support for em86 (like binfmt_em86, for Alpha AXP only): | ||
81 | 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 | ||
82 | 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 | ||
83 | |||
84 | - enable support for packed DOS applications (pre-configured dosemu hdimages): | ||
85 | echo ':DEXE:M::\x0eDEX::/usr/bin/dosexec:' > register | ||
86 | |||
87 | - enable support for Windows executables using wine: | ||
88 | echo ':DOSWin:M::MZ::/usr/local/bin/wine:' > register | ||
89 | |||
90 | For java support see Documentation/java.txt | ||
91 | |||
92 | |||
93 | You can enable/disable binfmt_misc or one binary type by echoing 0 (to disable) | ||
94 | or 1 (to enable) to /proc/sys/fs/binfmt_misc/status or /proc/.../the_name. | ||
95 | Catting the file tells you the current status of binfmt_misc/the entry. | ||
96 | |||
97 | You can remove one entry or all entries by echoing -1 to /proc/.../the_name | ||
98 | or /proc/sys/fs/binfmt_misc/status. | ||
99 | |||
100 | |||
101 | HINTS: | ||
102 | ====== | ||
103 | |||
104 | If you want to pass special arguments to your interpreter, you can | ||
105 | write a wrapper script for it. See Documentation/java.txt for an | ||
106 | example. | ||
107 | |||
108 | Your interpreter should NOT look in the PATH for the filename; the kernel | ||
109 | passes it the full filename (or the file descriptor) to use. Using $PATH can | ||
110 | cause unexpected behaviour and can be a security hazard. | ||
111 | |||
112 | |||
113 | There is a web page about binfmt_misc at | ||
114 | http://www.tat.physik.uni-tuebingen.de/~rguenth/linux/binfmt_misc.html | ||
115 | |||
116 | Richard Günther <rguenth@tat.physik.uni-tuebingen.de> | ||