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TRUNCATE(2)                 BSD System Calls Manual                TRUNCATE(2)

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

     #include <unistd.h>

     ftruncate(int fildes, off_t length);

     truncate(const char *path, off_t length);

     Truncate() causes the file named by path or referenced by fildes to be
     truncated or extended to length bytes in size.  If the file previously
     was larger than this size, the extra data is lost. If the file was
     smaller than this size, it will be extended as if by writing bytes with
     the value zero.  With ftruncate(), the file must be open for writing.

     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.

     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

     [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, characters,
                        ters, or an entire path name exceeds {PATH_MAX} char-acters. characters.

     [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

     [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.


     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.

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

4.2 Berkeley Distribution        June 4, 1993        4.2 Berkeley Distribution