TRUNCATE(2) Linux Programmer's Manual TRUNCATE(2)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);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
truncate():
Since glibc 2.12
_BSD_SOURCE || _XOPEN_SOURCE >= 500 ||
_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED ||
_POSIX_C_SOURCE >= 200809L
Before glibc 2.12:
_BSD_SOURCE || _XOPEN_SOURCE >= 500 ||
_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
ftruncate():
Since glibc 2.12:
_BSD_SOURCE || _XOPEN_SOURCE >= 500 ||
_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED ||
_POSIX_C_SOURCE >= 200809L
Between glibc 2.3.5 and 2.11
_BSD_SOURCE || _XOPEN_SOURCE >= 500 ||
_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED ||
_POSIX_C_SOURCE >= 200112L
Before glibc 2.3.5:
_BSD_SOURCE || _XOPEN_SOURCE >= 500 ||
_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
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 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.
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. (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 translat‐
ing 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.
CONFORMING TO
4.4BSD, SVr4, POSIX.1-2001 (these calls first appeared in
4.2BSD).
NOTES
The above description is 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.
SEE ALSOopen(2), stat(2), path_resolution(7)COLOPHON
This page is part of release 3.27 of the Linux man-pages
project. A description of the project, and information
about reporting bugs, can be found at http://www.ker‐
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Linux 2010-09-20 TRUNCATE(2)