ftruncate()

NAME

ftruncate(), truncate() - truncate a file to a specified length

SYNOPSIS

#include <unistd.h>


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

DESCRIPTION

The ftruncate(2) function truncates the file referenced by fd to at most length bytes in size. The truncate(2) call also truncates a file, but the file is specified by the pathname path.

If the file previously was larger than length, the extra data is lost. If the file was shorter, the extra space is filled with zeroes.

For ftruncate, the file described by fd must have been opened for writing. For truncate, the calling process must simply have write permission on the file.

Calling truncate(2) or ftruncate(2) on an open file won't affect any file offsets associated with file descriptors for that file.

If the file size is actually changed, the st_ctime and st_mtime fields are marked for change. The s_ISUID and the S_ISGID bits on the file permission will be cleared.

RETURN VALUES

The ftruncate(2) function returns 0 on success. On failure, it returns -1 and sets the global variable errno

ERRORS

The ftruncate(2) function succeeds unless:

[EBADF]

The fd is not a valid descriptor.

[EFBIG]

The length argument was longer than the maximum file size.

[EINTR]

The call was interrupted by a signal.

[EINVAL]

The file descriptor fd is not open for writing, or the file descriptor fd points to a socket, not a file, or the length argument was less than zero.

[EIO]

An I/O error occurred while reading or writing to a file system.

[ESPIPE]

The fd refers to a FIFO or a pipe.

The truncate(2) call will fail for these reasons:

[EACCES]

Some directory component of path denied search permission to the process, or the process didn't have write permission on the file.

[EFBIG]

The length argument was longer than the maximum file size.

[EINTR]

The call was interrupted by a signal.

[EINVAL]

The length argument was less than 0.

[EIO]

An I/O error occurred while reading or writing to a file system.

[EISDIR]

The path ends in a directory.

[ELOOP]

Too many symbolic links were encountered while resolving path.

[ENAMETOOLONG]

The total length of the path was longer than {PATH_MAX}, or the length of some component of path was longer than {NAME_MAX}, or the resolution of a symbolic link produced an intermediate result that was longer than {PATH_MAX}.

[ENOENT]

Either path was an empty string, or some component of path named a nonexistent file.

[ENOTDIR]

Some component of the path prefix of path is not a directory.

[EROFS]

The file named by path is on a read-only filesystem.

SEE ALSO

open(2)