TRUNCATE(2)               FreeBSD System Calls Manual              TRUNCATE(2)

NAME
     truncate, ftruncate - truncate or extend 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
     The truncate() system call causes the file named by path or referenced by
     fd to be truncated 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.

     The ftruncate() system call causes the file or shared memory object
     backing the file descriptor fd to be truncated or extended to length
     bytes in size.  The file descriptor must be a valid file descriptor open
     for writing.  The file position pointer associated with the file
     descriptor fd will not be modified.

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.  If the file to be modified is not a directory or a regular file,
     the truncate() call has no effect and returns the value 0.

ERRORS
     The truncate() system call succeeds unless:

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

     [ENAMETOOLONG]     A component of a pathname exceeded 255 characters, or
                        an entire path name exceeded 1023 characters.

     [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
                        translating the pathname.

     [EPERM]            The named file has its immutable or append-only flag
                        set, see the chflags(2) manual page for more
                        information.

     [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.

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

     [EINVAL]           The length argument was less than 0.

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

     [EINTEGRITY]       Corrupted data was detected while reading from the
                        file system.

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

     The ftruncate() system call succeeds unless:

     [EBADF]            The fd argument is not a valid descriptor.

     [EINVAL]           The fd argument references a file descriptor that is
                        not a regular file or shared memory object.

     [EINVAL]           The fd descriptor is not open for writing.

SEE ALSO
     chflags(2), open(2), shm_open(2)

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

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

     Historically, the use of truncate() or ftruncate() to extend a file was
     not portable, but this behavior became required in IEEE Std 1003.1-2008
     ("POSIX.1").

FreeBSD 13.1-RELEASE-p6         March 30, 2020         FreeBSD 13.1-RELEASE-p6