libmagic(3) — Linux manual page


LIBMAGIC(3)           BSD Library Functions Manual           LIBMAGIC(3)

NAME         top

     magic_open, magic_close, magic_error, magic_errno,
     magic_descriptor, magic_buffer, magic_getflags, magic_setflags,
     magic_check, magic_compile, magic_list, magic_load,
     magic_load_buffers, magic_setparam, magic_getparam, magic_version —
     Magic number recognition library

LIBRARY         top

     Magic Number Recognition Library (libmagic, -lmagic)

SYNOPSIS         top

     #include <magic.h>

     magic_open(int flags);

     magic_close(magic_t cookie);

     const char *
     magic_error(magic_t cookie);

     magic_errno(magic_t cookie);

     const char *
     magic_descriptor(magic_t cookie, int fd);

     const char *
     magic_file(magic_t cookie, const char *filename);

     const char *
     magic_buffer(magic_t cookie, const void *buffer, size_t length);

     magic_getflags(magic_t cookie);

     magic_setflags(magic_t cookie, int flags);

     magic_check(magic_t cookie, const char *filename);

     magic_compile(magic_t cookie, const char *filename);

     magic_list(magic_t cookie, const char *filename);

     magic_load(magic_t cookie, const char *filename);

     magic_load_buffers(magic_t cookie, void **buffers, size_t *sizes,
         size_t nbuffers);

     magic_getparam(magic_t cookie, int param, void *value);

     magic_setparam(magic_t cookie, int param, const void *value);


DESCRIPTION         top

     These functions operate on the magic database file which is
     described in magic(4).

     The function magic_open() creates a magic cookie pointer and
     returns it.  It returns NULL if there was an error allocating the
     magic cookie.  The flags argument specifies how the other magic
     functions should behave:

     MAGIC_NONE      No special handling.

     MAGIC_DEBUG     Print debugging messages to stderr.

     MAGIC_SYMLINK   If the file queried is a symlink, follow it.

     MAGIC_COMPRESS  If the file is compressed, unpack it and look at
                     the contents.

     MAGIC_DEVICES   If the file is a block or character special device,
                     then open the device and try to look in its

                     Return a MIME type string, instead of a textual

                     Return a MIME encoding, instead of a textual

     MAGIC_MIME      A shorthand for MAGIC_MIME_TYPE |

     MAGIC_CONTINUE  Return all matches, not just the first.

     MAGIC_CHECK     Check the magic database for consistency and print
                     warnings to stderr.

                     On systems that support utime(3) or utimes(2),
                     attempt to preserve the access time of files

     MAGIC_RAW       Don't translate unprintable characters to a \ooo
                     octal representation.

     MAGIC_ERROR     Treat operating system errors while trying to open
                     files and follow symlinks as real errors, instead
                     of printing them in the magic buffer.

     MAGIC_APPLE     Return the Apple creator and type.

                     Return a slash-separated list of extensions for
                     this file type.

                     Don't report on compression, only report about the
                     uncompressed data.

                     Don't check for EMX application type (only on EMX).

                     Don't allow decompressors that use fork.

                     Don't get extra information on MS Composite
                     Document Files.

                     Don't look inside compressed files.

                     Don't print ELF details.

                     Don't check text encodings.

                     Don't consult magic files.

                     Don't examine tar files.

                     Don't check for various types of text files.

                     Don't look for known tokens inside ascii files.

                     Don't examine JSON files.

                     Don't examine CSV files.

     The magic_close() function closes the magic(4) database and
     deallocates any resources used.

     The magic_error() function returns a textual explanation of the
     last error, or NULL if there was no error.

     The magic_errno() function returns the last operating system error
     number (errno(2)) that was encountered by a system call.

     The magic_file() function returns a textual description of the
     contents of the filename argument, or NULL if an error occurred.
     If the filename is NULL, then stdin is used.

     The magic_descriptor() function returns a textual description of
     the contents of the fd argument, or NULL if an error occurred.

     The magic_buffer() function returns a textual description of the
     contents of the buffer argument with length bytes size.

     The magic_getflags() functions returns a value representing current
     flags set.

     The magic_setflags() function sets the flags described above.  Note
     that using both MIME flags together can also return extra
     information on the charset.

     The magic_check() function can be used to check the validity of
     entries in the colon separated database files passed in as
     filename, or NULL for the default database.  It returns 0 on
     success and -1 on failure.

     The magic_compile() function can be used to compile the colon
     separated list of database files passed in as filename, or NULL for
     the default database.  It returns 0 on success and -1 on failure.
     The compiled files created are named from the basename(1) of each
     file argument with “.mgc” appended to it.

     The magic_list() function dumps all magic entries in a human
     readable format, dumping first the entries that are matched against
     binary files and then the ones that match text files.  It takes and
     optional filename argument which is a colon separated list of
     database files, or NULL for the default database.

     The magic_load() function must be used to load the colon separated
     list of database files passed in as filename, or NULL for the
     default database file before any magic queries can performed.

     The default database file is named by the MAGIC environment
     variable.  If that variable is not set, the default database file
     name is /usr/local/share/misc/magic.  magic_load() adds “.mgc” to
     the database filename as appropriate.

     The magic_load_buffers() function takes an array of size nbuffers
     of buffers with a respective size for each in the array of sizes
     loaded with the contents of the magic databases from the
     filesystem.  This function can be used in environment where the
     magic library does not have direct access to the filesystem, but
     can access the magic database via shared memory or other IPC means.

     The magic_getparam() and magic_setparam() allow getting and setting
     various limits related to the magic library.

           Parameter                    Type      Default
           MAGIC_PARAM_INDIR_MAX        size_t    15
           MAGIC_PARAM_NAME_MAX         size_t    30
           MAGIC_PARAM_ELF_NOTES_MAX    size_t    256
           MAGIC_PARAM_ELF_PHNUM_MAX    size_t    128
           MAGIC_PARAM_ELF_SHNUM_MAX    size_t    32768
           MAGIC_PARAM_REGEX_MAX        size_t    8192
           MAGIC_PARAM_BYTES_MAX        size_t    1048576

     The MAGIC_PARAM_INDIR_RECURSION parameter controls how many levels
     of recursion will be followed for indirect magic entries.

     The MAGIC_PARAM_NAME_RECURSION parameter controls how many levels
     of recursion will be followed for for name/use calls.

     The MAGIC_PARAM_NAME_MAX parameter controls the maximum number of
     calls for name/use.

     The MAGIC_PARAM_NOTES_MAX parameter controls how many ELF notes
     will be processed.

     The MAGIC_PARAM_PHNUM_MAX parameter controls how many ELF program
     sections will be processed.

     The MAGIC_PARAM_SHNUM_MAX parameter controls how many ELF sections
     will be processed.

     The magic_version() command returns the version number of this
     library which is compiled into the shared library using the
     constant MAGIC_VERSION from <magic.h>.  This can be used by client
     programs to verify that the version they compile against is the
     same as the version that they run against.

RETURN VALUES         top

     The function magic_open() returns a magic cookie on success and
     NULL on failure setting errno to an appropriate value.  It will set
     errno to EINVAL if an unsupported value for flags was given.  The
     magic_list(), magic_load(), magic_compile(), and magic_check()
     functions return 0 on success and -1 on failure.  The
     magic_buffer(), magic_getpath(), and magic_file(), functions return
     a string on success and NULL on failure.  The magic_error()
     function returns a textual description of the errors of the above
     functions, or NULL if there was no error.  The magic_version()
     always returns the version number of the library.  Finally,
     magic_setflags() returns -1 on systems that don't support utime(3),
     or utimes(2) when MAGIC_PRESERVE_ATIME is set.

FILES         top

     /usr/local/share/misc/magic      The non-compiled default magic
     /usr/local/share/misc/magic.mgc  The compiled default magic

SEE ALSO         top

     file(1), magic(4)

BUGS         top

     The results from magic_buffer() and magic_file() where the buffer
     and the file contain the same data can produce different results,
     because in the magic_file() case, the program can lseek(2) and
     stat(2) the file descriptor.

AUTHORS         top

     Måns Rullgård Initial libmagic implementation, and configuration.
     Christos Zoulas API cleanup, error code and allocation handling.

COLOPHON         top

     This page is part of the file (a file type guesser) project.
     Information about the project can be found at  If you have a bug report for this
     manual page, see ⟨⟩.  This page
     was obtained from the project's upstream Git read-only mirror of
     the CVS repository ⟨⟩ on 2022-12-17.
     (At that time, the date of the most recent commit that was found in
     the repository was 2022-12-14.)  If you discover any rendering
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     (which is not part of the original manual page), send a mail to

BSD                        September 15, 2022                        BSD