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

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

SYNOPSIS
     #include <&lt;unistd.h>&gt;

     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 be trun-
     cated or extended to length bytes in size.  If the file 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.

RETURN VALUES
     Upon successful completion, the value 0 is returned; otherwise the
     value -1 is returned and the global variable errno is set to indicate the
     error.

ERRORS
     truncate() and ftruncate() will succeed unless:

     [EINVAL]           The length is a negative value.

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

     In addition, truncate() may return the following errors:

     [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 pathname (including the terminating
                        NUL) exceeded PATH_MAX bytes.

     [ENOENT]           The named file does not exist.

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

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

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

     [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.

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

     ftruncate() may return the following errors:

     [EBADF]            The fd is not a valid descriptor.

     [EINVAL]           The fd references a socket, not a file.

     [EINVAL]           The fd is not open for writing.

SEE ALSO
     open(2)

STANDARDS
     The truncate() and ftruncate() functions conform to IEEE Std 1003.1-2008
     (``POSIX.1'').

HISTORY
     The truncate() and ftruncate() system calls first appeared in 4.1cBSD.

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.

BSD                             April 28, 2017                             BSD