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truncate

shrink or extend the size of a file to the specified size


  1. truncate.1.man
  2. truncate.2.man


1. truncate.1.man

Manpage of TRUNCATE

TRUNCATE

Section: User Commands (1)
Updated: October 2011
Index Return to Main Contents
 

NAME

truncate - shrink or extend the size of a file to the specified size  

SYNOPSIS

truncate OPTION... FILE...  

DESCRIPTION

Shrink or extend the size of each FILE to the specified size

A FILE argument that does not exist is created.

If a FILE is larger than the specified size, the extra data is lost. If a FILE is shorter, it is extended and the extended part (hole) reads as zero bytes.

Mandatory arguments to long options are mandatory for short options too.

-c, --no-create
do not create any files
-o, --io-blocks
treat SIZE as number of IO blocks instead of bytes
-r, --reference=RFILE
base size on RFILE
-s, --size=SIZE
set or adjust the file size by SIZE
--help
display this help and exit
--version
output version information and exit

SIZE may be (or may be an integer optionally followed by) one of following: KB 1000, K 1024, MB 1000*1000, M 1024*1024, and so on for G, T, P, E, Z, Y.

SIZE may also be prefixed by one of the following modifying characters: `+' extend by, `-' reduce by, `<' at most, `>' at least, `/' round down to multiple of, `%' round up to multiple of.  

AUTHOR

Written by Padraig Brady.  

REPORTING BUGS

Report truncate bugs to bug-coreutils@gnu.org
GNU coreutils home page: <http://www.gnu.org/software/coreutils/>
General help using GNU software: <http://www.gnu.org/gethelp/>
Report truncate translation bugs to <http://translationproject.org/team/>  

COPYRIGHT

Copyright © 2011 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl>.
This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law.  

SEE ALSO

dd(1), truncate(2), ftruncate(2)

The full documentation for truncate is maintained as a Texinfo manual. If the info and truncate programs are properly installed at your site, the command

info coreutils aqtruncate invocationaq

should give you access to the complete manual.


 

Index

NAME
SYNOPSIS
DESCRIPTION
AUTHOR
REPORTING BUGS
COPYRIGHT
SEE ALSO

This document was created by man2html using the manual pages.
Time: 17:32:51 GMT, October 23, 2013

2. truncate.2.man

Manpage of TRUNCATE

TRUNCATE

Section: Linux Programmer's Manual (2)
Updated: 2010-11-21
Index Return to Main Contents
 

NAME

truncate, ftruncate - truncate a file to a specified length  

SYNOPSIS

#include <unistd.h>
#include <sys/types.h>

int truncate(const char *path, off_t length);
int ftruncate(int fd, off_t length);

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

truncate():

_BSD_SOURCE || _XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
|| /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L

ftruncate():

_BSD_SOURCE || _XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
|| /* Since glibc 2.3.5: */ _POSIX_C_SOURCE >= 200112L
 

DESCRIPTION

The truncate() and ftruncate() functions cause the regular file named by path or referenced by fd to be truncated to a size of precisely length bytes.

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\0aq).

The file offset is not changed.

If the size changed, then the st_ctime and st_mtime fields (respectively, time of last status change and time of last modification; see stat(2)) for the file are updated, and the set-user-ID and set-group-ID permission bits may be cleared.

With ftruncate(), the file must be open for writing; with truncate(), the file must be writable.  

RETURN VALUE

On success, zero is returned. On error, -1 is returned, and errno is set appropriately.  

ERRORS

For truncate():
EACCES
Search permission is denied for a component of the path prefix, or the named file is not writable by the user. (See also path_resolution(7).)
EFAULT
Path points outside the process's allocated address space.
EFBIG
The argument length is larger than the maximum file size. (XSI)
EINTR
A signal was caught during execution.
EINVAL
The argument length is negative or larger than the maximum file size.
EIO
An I/O error occurred updating the inode.
EINTR
While blocked waiting to complete, the call was interrupted by a signal handler; see fcntl(2) and signal(7).
EISDIR
The named file is a directory.
ELOOP
Too many symbolic links were encountered in translating the pathname.
ENAMETOOLONG
A component of a pathname exceeded 255 characters, or an entire pathname exceeded 1023 characters.
ENOENT
The named file does not exist.
ENOTDIR
A component of the path prefix is not a directory.
EPERM
The underlying file system does not support extending a file beyond its current size.
EROFS
The named file resides on a read-only file system.
ETXTBSY
The file is a pure procedure (shared text) file that is being executed.

For ftruncate() the same errors apply, but instead of things that can be wrong with path, we now have things that can be wrong with the file descriptor, fd:

EBADF
fd is not a valid descriptor.
EBADF or EINVAL
fd is not open for writing.
EINVAL
fd does not reference a regular file.
 

CONFORMING TO

4.4BSD, SVr4, POSIX.1-2001 (these calls first appeared in 4.2BSD).  

NOTES

The details in DESCRIPTION are for XSI-compliant systems. For non-XSI-compliant systems, the POSIX standard allows two behaviors for ftruncate() when length exceeds the file length (note that truncate() 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 truncate() and ftruncate() to be used to extend a file beyond its current length: a notable example on Linux is VFAT.

The original Linux truncate() and ftruncate() system calls were not designed to handle large file offsets. Consequently, Linux 2.4 added truncate64() and ftruncate64() system calls that handle large files. However, these details can be ignored by applications using glibc, whose wrapper functions transparently employ the more recent system calls where they are available.  

BUGS

A header file bug in glibc 2.12 meant that the minimum value of _POSIX_C_SOURCE required to expose the declaration of ftruncate() was 200809L instead of 200112L. This has been fixed in later glibc versions.  

SEE ALSO

open(2), stat(2), path_resolution(7)  

COLOPHON

This page is part of release 3.32 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.


 

Index

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
CONFORMING TO
NOTES
BUGS
SEE ALSO
COLOPHON

This document was created by man2html using the manual pages.
Time: 17:32:51 GMT, October 23, 2013

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