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truncate(2)                 BSD System Calls Manual                truncate(2)


NAME

     ftruncate, truncate -- truncate or extend a file to a specified length


SYNOPSIS

     #include <unistd.h>

     int
     ftruncate(int fildes, off_t length);

     int
     truncate(const char *path, off_t length);


DESCRIPTION

     ftruncate() and truncate() cause the file named by path, or referenced by
     fildes, to be truncated (or extended) to length bytes in size. If the
     file size exceeds length, any extra data is discarded. If the file size
     is smaller than length, the file is extended and filled with zeros to the
     indicated length.  The ftruncate() form requires the file to be open for
     writing.

     Note: ftruncate() and truncate() do not modify the current file offset
     for any open file descriptions associated with the file.


RETURN VALUES

     A value of 0 is returned if the call succeeds.  If the call fails a -1 is
     returned, and the global variable errno specifies the error.


ERRORS

     The ftruncate() system call will fail if:

     [EBADF]            fildes is not a valid descriptor open for writing.

     [EFBIG]            The file is a regular file and length is greater than
                        the offset maximum established in the open file
                        description associated with fildes.

     [EINVAL]           fildes references a socket, not a file.

     [EINVAL]           fildes is not open for writing.

     [EROFS]            The named file resides on a read-only file system.

     The truncate() system call will fail if:

     [EACCES]           Search permission is denied for a component of the
                        path prefix.

     [EACCES]           The named file is not writable by the user.

     [EFAULT]           Path points outside the process's allocated address
                        space.

     [EISDIR]           The named file is a directory.

     [ELOOP]            Too many symbolic links are encountered in translating
                        the pathname.  This is taken to be indicative of a
                        looping symbolic link.

     [ENAMETOOLONG]     A component of a pathname exceeds {NAME_MAX} charac-
                        ters, or an entire path name exceeds {PATH_MAX} char-
                        acters.

     [ENOENT]           The named file does not exist.

     [ENOTDIR]          A component of the path prefix is not a directory.

     [EROFS]            The named file resides on a read-only file system.

     [ETXTBSY]          The file is a pure procedure (shared text) file that
                        is being executed.

     The ftruncate() and truncate() system calls will fail if:

     [EFBIG]            The length argument was greater than the maximum file
                        size.

     [EINTR]            A signal is caught during execution.

     [EINVAL]           The length argument is less than 0.

     [EIO]              An I/O error occurred while reading from or writing to
                        a file system.


SEE ALSO

     open(2)


BUGS

     These calls should be generalized to allow ranges of bytes in a file to
     be discarded.

     Use of truncate() to extend a file is not portable.


HISTORY

     The truncate() and ftruncate() function calls appeared in 4.2BSD.

4.2 Berkeley Distribution        June 4, 1993        4.2 Berkeley Distribution

Mac OS X 10.9.1 - Generated Mon Jan 6 18:32:57 CST 2014
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