TRUNCATE(2) BSD System Calls Manual TRUNCATE(2)
truncate, ftruncate -- truncate or extend a file to a specified length
truncate(const char *path, off_t length);
ftruncate(int fd, off_t length);
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.
Upon successful completion, the value 0 is returned; otherwise the
value -1 is returned and the global variable errno is set to indicate the
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
[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
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.
The truncate() and ftruncate() functions conform to IEEE Std 1003.1-2008
The truncate() and ftruncate() system calls first appeared in 4.1cBSD.
These calls should be generalized to allow ranges of bytes in a file to
Use of truncate() to extend a file is not portable.
BSD April 28, 2017 BSD