path: root/Documentation/binfmt_misc.txt
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authorLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
committerLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
commit1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (patch)
tree0bba044c4ce775e45a88a51686b5d9f90697ea9d /Documentation/binfmt_misc.txt
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!
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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
+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.
+If you want to pass special arguments to your interpreter, you can
+write a wrapper script for it. See Documentation/java.txt for an
+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
+Richard GŁnther <rguenth@tat.physik.uni-tuebingen.de>