add note about finding the end of memory

[unix-history] / usr / src / lib / libc / sys / truncate.2

.\" Copyright (c) 1983 Regents of the University of California.
.\" All rights reserved.  The Berkeley software License Agreement
.\" specifies the terms and conditions for redistribution.
.\"
.\"	@(#)truncate.2	6.6 (Berkeley) %G%
.\"
.TH TRUNCATE 2 ""
.UC 5
.SH NAME
truncate \- truncate a file to a specified length
.SH SYNOPSIS
.nf
.ft B
truncate(path, length)
char *path;
off_t length;
.PP
.ft B
ftruncate(fd, length)
int fd;
off_t length;
.fi
.SH DESCRIPTION
.I Truncate
causes the file named by
.I path
or referenced by
.I fd
to be truncated to at most
.I length
bytes in size.  If the file previously
was larger than this size, the extra data
is lost.
With
.IR ftruncate ,
the file must be open for writing.
.SH "RETURN VALUES
A value of 0 is returned if the call succeeds.  If the call
fails a \-1 is returned, and the global variable \fIerrno\fP
specifies the error.
.SH "ERRORS
.I Truncate
succeeds unless:
.TP 15
[ENOTDIR]
A component of the path prefix is not a directory.
.TP 15
[EINVAL]
The pathname contains a character with the high-order bit set.
.TP 15
[ENAMETOOLONG]
A component of a pathname exceeded 255 characters,
or an entire path name exceeded 1023 characters.
.TP 15
[ENOENT]
The named file does not exist.
.TP 15
[EACCES]
Search permission is denied for a component of the path prefix.
.TP 15
[EACCES]
The named file is not writable by the user.
.TP 15
[ELOOP]
Too many symbolic links were encountered in translating the pathname.
.TP 15
[EISDIR]
The named file is a directory.
.TP 15
[EROFS]
The named file resides on a read-only file system.
.TP 15
[ETXTBSY]
The file is a pure procedure (shared text) file that is being executed.
.TP 15
[EIO]
An I/O error occurred updating the inode.
.TP 15
[EFAULT]
.I Path
points outside the process's allocated address space.
.PP
.I Ftruncate
succeeds unless:
.TP 15
[EBADF]
The
.I fd
is not a valid descriptor.
.TP 15
[EINVAL]
The
.I fd
references a socket, not a file.
.TP 15
[EINVAL]
The
.I fd
is not open for writing.
.SH "SEE ALSO"
open(2)
.SH BUGS
These calls should be generalized to allow ranges
of bytes in a file to be discarded.