TRUNCATE(2) BSD System Calls Manual TRUNCATE(2)NAME
truncate, ftruncate — truncate or extend a file to a specified length
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 previously 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
A value of 0 is returned if the call succeeds. If the call fails a -1 is
returned, and the global variable errno specifies the error.
ERRORSTruncate() succeeds unless:
[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 path name exceeded {PATH_MAX} char‐
acters.
[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)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.
HISTORY
The truncate() and ftruncate() function calls appeared in 4.2BSD.
4.2 Berkeley Distribution June 4, 1993 4.2 Berkeley Distribution