4.2BSD/usr/man/man2/truncate.2

.TH TRUNCATE 2 "7 July 1983"
.UC 4
.SH NAME
truncate \- truncate a file to a specified length
.SH SYNOPSIS
.nf
.ft B
truncate(path, length)
char *path;
int length;
.PP
.ft B
ftruncate(fd, length)
int fd, 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
[EPERM]
The pathname contains a character with the high-order bit set.
.TP 15
[ENOENT]
The pathname was too long.
.TP 15
[ENOTDIR]
A component of the path prefix of \fIpath\fP is not a directory.
.TP 15
[ENOENT]
The named file does not exist.
.TP 15
[EACCES]
A component of the \fIpath\fP prefix denies search permission.
.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
[EFAULT]
.I Name
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.
.SH "SEE ALSO"
open(2)
.SH BUGS
Partial blocks discarded as the result of truncation
are not zero filled; this can result in holes in files
which do not read as zero.
.PP
These calls should be generalized to allow ranges
of bytes in a file to be discarded.