.\" Copyright (c) 1983, 1991 The Regents of the University of California.
.\" All rights reserved.
.\"
+.\" %%%LICENSE_START(BSD_4_CLAUSE_UCB)
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
+.\" %%%LICENSE_END
.\"
.\" @(#)truncate.2 6.9 (Berkeley) 3/10/91
.\"
.\" Modified 2002-04-06 by Andries Brouwer <aeb@cwi.nl>
.\" Modified 2004-06-23 by Michael Kerrisk <mtk.manpages@gmail.com>
.\"
-.TH TRUNCATE 2 2011-09-08 "Linux" "Linux Programmer's Manual"
+.TH TRUNCATE 2 2019-03-06 "Linux" "Linux Programmer's Manual"
.SH NAME
truncate, ftruncate \- truncate a file to a specified length
.SH SYNOPSIS
.B #include <unistd.h>
.br
.B #include <sys/types.h>
-.sp
+.PP
.BI "int truncate(const char *" path ", off_t " length );
.br
.BI "int ftruncate(int " fd ", off_t " length );
-.sp
+.PP
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.ad l
-.PD 0
-.sp
+.PP
.BR truncate ():
.RS 4
-_BSD_SOURCE || _XOPEN_SOURCE\ >=\ 500 ||
-_XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
+_XOPEN_SOURCE\ >=\ 500
+.\" || _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
.br
-|| /* Since glibc 2.12: */ _POSIX_C_SOURCE\ >=\ 200809L
+ || /* Since glibc 2.12: */ _POSIX_C_SOURCE\ >=\ 200809L
+ || /* Glibc versions <= 2.19: */ _BSD_SOURCE
.RE
-.sp
+.PP
.BR ftruncate ():
.RS 4
-_BSD_SOURCE || _XOPEN_SOURCE\ >=\ 500 ||
-_XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
-.br
-|| /* Since glibc 2.3.5: */ _POSIX_C_SOURCE\ >=\ 200112L
+_XOPEN_SOURCE\ >=\ 500
+.\" || _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
+ || /* Since glibc 2.3.5: */ _POSIX_C_SOURCE\ >=\ 200112L
+ || /* Glibc versions <= 2.19: */ _BSD_SOURCE
.RE
-.PD
.ad b
.SH DESCRIPTION
The
to be truncated to a size of precisely
.I length
bytes.
-.LP
+.PP
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 (\(aq\\0\(aq).
-.LP
+the extended part reads as null bytes (\(aq\e0\(aq).
+.PP
The file offset is not changed.
-.LP
+.PP
If the size changed, then the st_ctime and st_mtime fields
(respectively, time of last status change and
time of last modification; see
-.BR stat (2))
+.BR inode (7))
for the file are updated,
-and the set-user-ID and set-group-ID permission bits may be cleared.
-.LP
+and the set-user-ID and set-group-ID mode bits may be cleared.
+.PP
With
.BR ftruncate (),
the file must be open for writing; with
.BR path_resolution (7).)
.TP
.B EFAULT
-.I Path
+The argument
+.I path
points outside the process's allocated address space.
.TP
.B EFBIG
A component of the path prefix is not a directory.
.TP
.B EPERM
-.\" This happens for at least MSDOS and VFAT file systems
+.\" This happens for at least MSDOS and VFAT filesystems
.\" on kernel 2.6.13
-The underlying file system does not support extending
+The underlying filesystem does not support extending
a file beyond its current size.
.TP
+.B EPERM
+The operation was prevented by a file seal; see
+.BR fcntl (2).
+.TP
.B EROFS
-The named file resides on a read-only file system.
+The named file resides on a read-only filesystem.
.TP
.B ETXTBSY
-The file is a pure procedure (shared text) file that is being executed.
+The file is an executable file that is being executed.
.PP
For
.BR ftruncate ()
.TP
.B EBADF
.I fd
-is not a valid descriptor.
+is not a valid file descriptor.
.TP
.BR EBADF " or " EINVAL
.I fd
.TP
.B EINVAL
.I fd
-does not reference a regular file.
+does not reference a regular file or a POSIX shared memory object.
+.TP
+.BR EINVAL " or " EBADF
+The file descriptor
+.I fd
+is not open for writing.
+POSIX permits, and portable applications should handle,
+either error for this case.
+(Linux produces
+.BR EINVAL .)
.SH CONFORMING TO
-4.4BSD, SVr4, POSIX.1-2001 (these calls first appeared in 4.2BSD).
+POSIX.1-2001, POSIX.1-2008,
+4.4BSD, SVr4 (these calls first appeared in 4.2BSD).
.\" POSIX.1-1996 has
.\" .BR ftruncate ().
.\" POSIX.1-2001 also has
.\" .BR ftruncate ()
.\" an additional EAGAIN error condition.
.SH NOTES
+.BR ftruncate ()
+can also be used to set the size of a POSIX shared memory object; see
+.BR shm_open (7).
+.PP
The details in DESCRIPTION are for XSI-compliant systems.
For non-XSI-compliant systems, the POSIX standard allows
two behaviors for
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
+when dealing with native filesystems.
+However, some nonnative filesystems do not permit
.BR truncate ()
and
.BR ftruncate ()
to be used to extend a file beyond its current length:
a notable example on Linux is VFAT.
.\" At the very least: OSF/1, Solaris 7, and FreeBSD conform, mtk, Jan 2002
-
+.PP
The original Linux
.BR truncate ()
and
However, these details can be ignored by applications using glibc, whose
wrapper functions transparently employ the more recent system calls
where they are available.
+.PP
+On some 32-bit architectures,
+the calling signature for these system calls differ,
+for the reasons described in
+.BR syscall (2).
.SH BUGS
A header file bug in glibc 2.12 meant that the minimum value of
.\" http://sourceware.org/bugzilla/show_bug.cgi?id=12037
was 200809L instead of 200112L.
This has been fixed in later glibc versions.
.SH SEE ALSO
+.BR truncate (1),
.BR open (2),
.BR stat (2),
.BR path_resolution (7)
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