Provided by: manpages-posix-dev_2013a-2_all 
PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface
may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface
may not be implemented on Linux.
NAME
truncate — truncate a file to a specified length
SYNOPSIS
#include <unistd.h> int truncate(const char *path, off_t length);
DESCRIPTION
The truncate() function shall cause the regular file named by path to have a size which shall be equal to
length bytes.
If the file previously was larger than length, the extra data is discarded. If the file was previously
shorter than length, its size is increased, and the extended area appears as if it were zero-filled.
The application shall ensure that the process has write permission for the file.
If the request would cause the file size to exceed the soft file size limit for the process, the request
shall fail and the implementation shall generate the SIGXFSZ signal for the process.
The truncate() function shall not modify the file offset for any open file descriptions associated with
the file. Upon successful completion, if the file size is changed, truncate() shall mark for update the
last data modification and last file status change timestamps of the file, and the S_ISUID and S_ISGID
bits of the file mode may be cleared.
RETURN VALUE
Upon successful completion, truncate() shall return 0. Otherwise, −1 shall be returned, and errno set to
indicate the error.
ERRORS
The truncate() function shall fail if:
EINTR A signal was caught during execution.
EINVAL The length argument was less than 0.
EFBIG or EINVAL
The length argument was greater than the maximum file size.
EIO An I/O error occurred while reading from or writing to a file system.
EACCES A component of the path prefix denies search permission, or write permission is denied on the
file.
EISDIR The named file is a directory.
ELOOP A loop exists in symbolic links encountered during resolution of the path argument.
ENAMETOOLONG
The length of a component of a pathname is longer than {NAME_MAX}.
ENOENT A component of path does not name an existing file or path is an empty string.
ENOTDIR
A component of the path prefix names an existing file that is neither a directory nor a symbolic
link to a directory, or the path argument contains at least one non-<slash> character and ends
with one or more trailing <slash> characters and the last pathname component names an existing
file that is neither a directory nor a symbolic link to a directory.
EROFS The named file resides on a read-only file system.
The truncate() function may fail if:
ELOOP More than {SYMLOOP_MAX} symbolic links were encountered during resolution of the path argument.
ENAMETOOLONG
The length of a pathname exceeds {PATH_MAX}, or pathname resolution of a symbolic link produced an
intermediate result with a length that exceeds {PATH_MAX}.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
None.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
open()
The Base Definitions volume of POSIX.1‐2008, <unistd.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition,
Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of Electrical and Electronics Engineers, Inc
and The Open Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the event
of any discrepancy between this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at
http://www.unix.org/online.html .
Any typographical or formatting errors that appear in this page are most likely to have been introduced
during the conversion of the source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .