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The executable formats are registered through a special purpose file system interface (similar to /proc). Debian-based distributions provide the functionality through an extra binfmt-support package.
The register file contains lines which define executable types to be handled. Each line is of the form:
- name is the name of the binary format.
- type is either E or M
- If it is E, the executable file format is identified by its filename extension: magic is the file extension to be associated with the binary format; offset and mask are ignored.
- If it is M, the format is identified by magic number at an absolute offset (defaults to 0) in the file and mask is a bitmask (defaults to all 0xFF) indicating which bits in the number are significant.
- interpreter is a program that is to be run with the matching file as an argument.
- flags (optional) is a string of letters, each controlling a certain aspect of interpreter invocation:
- P to preserve the original program name typed by user in command line — by adding that name to argv; the interpreter has to be aware of this so it can correctly pass that additional parameter to the interpreted program as its argv.
- O to open the program file and pass its file descriptor to the interpreter so it could read an otherwise unreadable file (for which the user does not have the "Read" permission).
- C to determine new process credentials based on program file rather than interpreter file (see setuid); implies O flag.
Each format has a corresponding file entry in the /proc/sys/fs/binfmt_misc directory which can be read to get information about a given file format.
- Documentation/binfmt_misc.txt in the Linux kernel source tree
- Guide:Running Mono Applications