TRUNCATE(2) BSD System Calls Manual TRUNCATE(2)NAME
truncate, ftruncate — truncate or extend a file to a specified length
Standard C Library (libc, -lc)
truncate(const char *path, off_t length);
ftruncate(int fd, off_t length);
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. 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
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.
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
[EACCES] The named file is not writable by the user.
[ELOOP] Too many symbolic links were encountered in translat‐
ing the pathname.
[EPERM] The named file has its immutable or append-only flag
set, see the chflags(2) manual page for more informa‐
[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
[EINVAL] The length argument was less than 0.
[EIO] An I/O error occurred updating the inode.
[EFAULT] The path argument points outside the process's allo‐
cated address space.
The ftruncate() system call succeeds unless:
[EBADF] The fd argument is not a valid descriptor.
[EINVAL] The fd argument references a socket, not a file.
[EINVAL] The fd descriptor is not open for writing.
SEE ALSOchflags(2), open(2)HISTORY
The truncate() system call appeared in 4.2BSD.
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 December 13, 2006 BSD