ftruncate(2) - NetBSD Manual Pages

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TRUNCATE(2)               NetBSD System Calls Manual               TRUNCATE(2)


NAME

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


LIBRARY

     Standard C Library (libc, -lc)


SYNOPSIS

     #include <unistd.h>

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

     int
     ftruncate(int fd, off_t length);


DESCRIPTION

     truncate() causes the file named by path or referenced by fd to have a
     size of length bytes.  If the file previously was larger than this size,
     the extra data is discarded.  If it was previously shorter than length,
     its size is increased to the specified value and the extended area
     appears as if it were zero-filled.

     With ftruncate(), the file must be open for writing; for truncate(), the
     process must have write permissions for 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

     Error return codes common to truncate() and ftruncate() are:

     [EISDIR]           The named file is 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.

     [EIO]              An I/O error occurred updating the inode.

     [ENOSPC]           There was no space in the filesystem to complete the
                        operation.

     Error codes specific to truncate() are:

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

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

     [ENOENT]           The named file does not exist.

     [EACCES]           Search permission is denied for a component of the
                        path prefix, or the named file is not writable by the
                        user.

     [ELOOP]            Too many symbolic links were encountered in translat-
                        ing the pathname.

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

     Error codes specific to ftruncate() are:

     [EBADF]            The fd is not a valid descriptor.

     [EINVAL]           The fd references a socket, not a file, or the fd is
                        not open for writing.


SEE ALSO

     open(2)


STANDARDS

     Use of truncate() to extend a file is an IEEE Std 1003.1-2004
     (``POSIX.1'') extension, and is thus not portable.  Files can be extended
     in a portable way seeking (using lseek(2)) to the required size and writ-
     ing a single character with write(2).


HISTORY

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


BUGS

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

NetBSD 5.1                      March 16, 2008                      NetBSD 5.1