153 lines
4.3 KiB
Groff
153 lines
4.3 KiB
Groff
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.\" $NetBSD: truncate.2,v 1.26 2010/05/31 12:16:20 njoly Exp $
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.\"
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.\" Copyright (c) 1983, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)truncate.2 8.1 (Berkeley) 6/4/93
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.\"
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.Dd March 16, 2008
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.Dt TRUNCATE 2
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.Os
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.Sh NAME
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.Nm truncate ,
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.Nm ftruncate
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.Nd truncate a file to a specified length
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In unistd.h
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.Ft int
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.Fn truncate "const char *path" "off_t length"
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.Ft int
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.Fn ftruncate "int fd" "off_t length"
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.Sh DESCRIPTION
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.Fn truncate
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causes the file named by
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.Fa path
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or referenced by
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.Fa fd
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to have a size of
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.Fa length
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bytes.
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If the file previously was larger than this size, the extra data is discarded.
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If it was previously shorter than
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.Fa length ,
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its size is increased to the specified value and
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the extended area appears as if it were zero-filled.
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.Pp
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With
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.Fn ftruncate ,
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the file must be open for writing; for
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.Fn truncate ,
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the process must have write permissions for the file.
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.Sh RETURN VALUES
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A value of 0 is returned if the call succeeds.
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If the call fails a \-1 is returned, and the global variable
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.Va errno
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specifies the error.
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.Sh ERRORS
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Error return codes common to
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.Fn truncate
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and
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.Fn ftruncate
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are:
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.Bl -tag -width Er
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.It Bq Er EISDIR
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The named file is a directory.
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.It Bq Er EROFS
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The named file resides on a read-only file system.
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.It Bq Er ETXTBSY
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The file is a pure procedure (shared text) file that is being executed.
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.It Bq Er EIO
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An I/O error occurred updating the inode.
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.It Bq Er ENOSPC
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There was no space in the filesystem to complete the operation.
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.El
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.Pp
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Error codes specific to
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.Fn truncate
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are:
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.Bl -tag -width Er
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.It Bq Er ENOTDIR
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A component of the path prefix is not a directory.
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.It Bq Er ENAMETOOLONG
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A component of a pathname exceeded
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.Brq Dv NAME_MAX
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characters, or an entire path name exceeded
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.Brq Dv PATH_MAX
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characters.
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.It Bq Er ENOENT
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The named file does not exist.
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.It Bq Er EACCES
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Search permission is denied for a component of the path prefix, or
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the named file is not writable by the user.
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.It Bq Er ELOOP
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Too many symbolic links were encountered in translating the pathname.
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.It Bq Er EFAULT
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.Fa path
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points outside the process's allocated address space.
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.El
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.Pp
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Error codes specific to
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.Fn ftruncate
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are:
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.Bl -tag -width Er
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.It Bq Er EBADF
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The
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.Fa fd
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is not a valid descriptor.
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.It Bq Er EINVAL
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The
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.Fa fd
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references a socket, not a file, or
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the
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.Fa fd
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is not open for writing.
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.El
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.Sh SEE ALSO
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.Xr open 2
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.Sh STANDARDS
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Use of
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.Fn truncate
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to extend a file is an
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.St -p1003.1-2004
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extension, and is thus not portable.
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Files can be extended in a portable way seeking (using
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.Xr lseek 2 )
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to the required size and writing a single character with
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.Xr write 2 .
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.Sh HISTORY
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The
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.Fn truncate
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and
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.Fn ftruncate
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function calls appeared in
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.Bx 4.2 .
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.Sh BUGS
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These calls should be generalized to allow ranges
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of bytes in a file to be discarded.
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