TRUNCATE

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
CONFORMING TO
NOTES
SEE ALSO

NAME

truncate, ftruncate − truncate a file to a specified length

SYNOPSIS

#include <unistd.h>
#include <sys/types.h>

int truncate(const char *path, off_t length);
int ftruncate(int
fd, off_t length);

DESCRIPTION

The truncate and ftruncate functions cause the regular file named by path or referenced by fd to be truncated to a size of precisely length bytes.

If the file previously was larger than this size, the extra data is lost. If the file previously was shorter, it is extended, and the extended part reads as zero bytes.

The file pointer is not changed.

If the size changed, then the ctime and mtime fields for the file are updated, and suid and sgid mode bits may be cleared.

With ftruncate, the file must be open for writing; with truncate, the file must be writable.

RETURN VALUE

On success, zero is returned. On error, −1 is returned, and errno is set appropriately.

ERRORS

For truncate:

EACCES

Search permission is denied for a component of the path prefix, or the named file is not writable by the user.

EFAULT

Path points outside the process’s allocated address space.

EFBIG

The argument length is larger than the maximum file size. (XSI)

EINTR

A signal was caught during execution.

EINVAL

The argument length is negative or larger than the maximum file size.

EIO

An I/O error occurred updating the inode.

EISDIR

The named file is a directory.

ELOOP

Too many symbolic links were encountered in translating the pathname.

ENAMETOOLONG

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

ENOENT

The named file does not exist.

ENOTDIR

A component of the path prefix is not 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.

For ftruncate the same errors apply, but instead of things that can be wrong with path, we now have things that can be wrong with fd:

EBADF

The fd is not a valid descriptor.

EBADF or EINVAL

The fd is not open for writing.

EINVAL

The fd does not reference a regular file.

CONFORMING TO

4.4BSD, SVr4 (these function calls first appeared in BSD 4.2). POSIX 1003.1-1996 has ftruncate. POSIX 1003.1-2001 also has truncate, as an XSI extension.

SVr4 documents additional truncate error conditions EMFILE, EMULTIHP, ENFILE, ENOLINK. SVr4 documents for ftruncate an additional EAGAIN error condition.

NOTES

The above description is for XSI-compliant systems. For non-XSI-compliant systems, the POSIX standard allows two behaviours for ftruncate when length exceeds the file length (note that truncate is not specified at all in such an environment): either returning an error, or extending the file. (Most Unices follow the XSI requirement.)

SEE ALSO

open(2)






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