TRUNCATE

Section: Linux Programmer's Manual (2)
Updated: 1998-12-21
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NAME

truncate, ftruncate - truncate 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);

DESCRIPTION

Truncate causes the file named by path or referenced by fd to be truncated to at most length bytes in size. If the file previously was larger than this size, the extra data is lost. If the file previously was shorter, it is unspecified whether the file is left unchanged or is extended. In the latter case the extended part reads as zero bytes. With ftruncate, the file must be open for writing.

RETURN VALUE

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

ERRORS

For truncate:

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 translating 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.

For ftruncate:

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.

CONFORMING TO

4.4BSD, SVr4 (these function calls first appeared in BSD 4.2). SVr4 documents additional truncate error conditions EINTR, EMFILE, EMULTIHP, ENAMETOOLONG, ENFILE, ENOLINK, ENOTDIR. SVr4 documents for ftruncate additional EAGAIN and EINTR error conditions. POSIX has ftruncate but not truncate.

The POSIX standard does not define what happens if the file has fewer bytes than length.

BUGS

These calls should be generalized to allow ranges of bytes in a file to be discarded.

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Time: 01:11:28 GMT, January 21, 2025