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():
_XOPEN_SOURCE >= 500
|| /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L
|| /* Glibc versions <= 2.19: */ _BSD_SOURCE
ftruncate():
_XOPEN_SOURCE >= 500
|| /* Since glibc 2.3.5: */ _POSIX_C_SOURCE >= 200112L
|| /* Glibc versions <= 2.19: */ _BSD_SOURCE
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 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. (See also
path_resolution(7).)
EFAULT The argument path points outside the process's allocated address
space.
EFBIG The argument length is larger than the maximum file size. (XSI)
EINTR While blocked waiting to complete, the call was interrupted by a
signal handler; see fcntl(2) and signal(7).
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
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 filesystem does not support extending a file
beyond its current size.
EPERM The operation was prevented by a file seal; see fcntl(2).
EROFS The named file resides on a read-only filesystem.
ETXTBSY
The file is an executable 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 file descriptor.
EBADF or EINVAL
fd is not open for writing.
EINVAL fd does not reference a regular file.
EINVAL or EBADF
The file descriptor fd is not open for writing. POSIX permits,
and portable applications should handle, either error for this
case. (Linux produces EINVAL.)
CONFORMING TO
POSIX.1-2001, POSIX.1-2008, 4.4BSD, SVr4 (these calls first appeared in 4.2BSD).
NOTES
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 filesystems. However, some nonnative filesystems 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. On some 32-bit architectures, the calling signature for these system calls differ, for the reasons described in syscall(2).
BUGS
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.
SEE ALSO
truncate(1), open(2), stat(2), path_resolution(7)
COLOPHON
This page is part of release 4.09 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.
Opportunity
Personal Opportunity - Free software gives you access to billions of dollars of software at no cost. Use this software for your business, personal use or to develop a profitable skill. Access to source code provides access to a level of capabilities/information that companies protect though copyrights. Open source is a core component of the Internet and it is available to you. Leverage the billions of dollars in resources and capabilities to build a career, establish a business or change the world. The potential is endless for those who understand the opportunity.
Business Opportunity - Goldman Sachs, IBM and countless large corporations are leveraging open source to reduce costs, develop products and increase their bottom lines. Learn what these companies know about open source and how open source can give you the advantage.
Free Software
Free Software provides computer programs and capabilities at no cost but more importantly, it provides the freedom to run, edit, contribute to, and share the software. The importance of free software is a matter of access, not price. Software at no cost is a benefit but ownership rights to the software and source code is far more significant.
Free Office Software - The Libre Office suite provides top desktop productivity tools for free. This includes, a word processor, spreadsheet, presentation engine, drawing and flowcharting, database and math applications. Libre Office is available for Linux or Windows.
Free Books
The Free Books Library is a collection of thousands of the most popular public domain books in an online readable format. The collection includes great classical literature and more recent works where the U.S. copyright has expired. These books are yours to read and use without restrictions.
Source Code - Want to change a program or know how it works? Open Source provides the source code for its programs so that anyone can use, modify or learn how to write those programs themselves. Visit the GNU source code repositories to download the source.
Education
Study at Harvard, Stanford or MIT - Open edX provides free online courses from Harvard, MIT, Columbia, UC Berkeley and other top Universities. Hundreds of courses for almost all major subjects and course levels. Open edx also offers some paid courses and selected certifications.
Linux Manual Pages - A man or manual page is a form of software documentation found on Linux/Unix operating systems. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts.
