| NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | NOTES | BUGS | SEE ALSO | COLOPHON | The Linux Programming Interface |
TRUNCATE(2) Linux Programmer's Manual TRUNCATE(2)
truncate, ftruncate - truncate a file to a specified length
#include <unistd.h>
#include <sys/types.h>
int truncate(const char *path, off_t length);
int ftruncate(int fd, off_t length);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
truncate():
_BSD_SOURCE || _XOPEN_SOURCE >= 500 ||
_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
|| /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L
ftruncate():
_BSD_SOURCE || _XOPEN_SOURCE >= 500 ||
_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
|| /* Since glibc 2.3.5: */ _POSIX_C_SOURCE >= 200112L
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 null bytes ('\0').
The file offset is not changed.
If the size changed, then the st_ctime and st_mtime fields (respectively, time
of last status change and time of last modification; see stat(2)) for the file
are updated, and the set-user-ID and set-group-ID permission bits may be
cleared.
With ftruncate(), the file must be open for writing; with truncate(), the file
must be writable.
On success, zero is returned. On error, -1 is returned, and errno is set
appropriately.
For truncate():
EACCES Search permission is denied for a component of the path prefix, or the
named file is not writable by the user. (See also path_resolution(7).)
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.
EINTR While blocked waiting to complete, the call was interrupted by a signal
handler; see fcntl(2) and signal(7).
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
pathname exceeded 1023 characters.
ENOENT The named file does not exist.
ENOTDIR
A component of the path prefix is not a directory.
EPERM The underlying file system does not support extending a file beyond its
current size.
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 the file descriptor, fd:
EBADF fd is not a valid descriptor.
EBADF or EINVAL
fd is not open for writing.
EINVAL fd does not reference a regular file.
4.4BSD, SVr4, POSIX.1-2001 (these calls first appeared in 4.2BSD).
The details in DESCRIPTION are for XSI-compliant systems. For non-XSI-
compliant systems, the POSIX standard allows two behaviors 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.
Like most UNIX implementations, Linux follows the XSI requirement when dealing
with native file systems. However, some nonnative file systems do not permit
truncate() and ftruncate() to be used to extend a file beyond its current
length: a notable example on Linux is VFAT.
The original Linux truncate() and ftruncate() system calls were not designed
to handle large file offsets. Consequently, Linux 2.4 added truncate64() and
ftruncate64() system calls that handle large files. However, these details
can be ignored by applications using glibc, whose wrapper functions
transparently employ the more recent system calls where they are available.
A header file bug in glibc 2.12 meant that the minimum value of
_POSIX_C_SOURCE required to expose the declaration of ftruncate() was 200809L
instead of 200112L. This has been fixed in later glibc versions.
open(2), stat(2), path_resolution(7)
This page is part of release 3.32 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can be found
at http://www.kernel.org/doc/man-pages/.
Linux 2010-11-21 TRUNCATE(2)
HTML rendering created 2010-12-03 by Michael Kerrisk, author of The Linux Programming Interface