TRUNCATE(2) BSD 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);
DESCRIPTIONTruncate() 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.
ERRORSTruncate() 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 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.
[EIO] An I/O error occurred updating the inode.
[EFAULT] Path points outside the process's allocated address
space.
Ftruncate() succeeds unless:
[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 ALSOopen(2)HISTORY
The truncate() function call appeared in 4.2BSD.
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 June 4, 1993 BSD
