tar: fix current_block confusion

[thirdparty/tar.git] / README

README for GNU tar
See the end of file for copying conditions.

* Introduction

Please glance through *all* sections of this
'README' file before starting configuration.  Also make sure you read files
'ABOUT-NLS' and 'INSTALL' if you are not familiar with them already.

If you got the 'tar' distribution in 'shar' format, time stamps ought to be
properly restored; do not ignore such complaints at 'unshar' time.

GNU 'tar' saves many files together into a single tape or disk
archive, and can restore individual files from the archive.  It includes
multivolume support, the ability to archive sparse files, automatic archive
compression/decompression, remote archives and special features that allow
'tar' to be used for incremental and full backups.  This distribution
also includes 'rmt', the remote tape server.  The 'mt' tape drive control
program is in the GNU 'cpio' distribution.

GNU 'tar' is derived from John Gilmore's public domain 'tar'.

See file 'ABOUT-NLS' for how to customize this program to your language.
See file 'COPYING' for copying conditions.
See file 'INSTALL' for compilation and installation instructions.
See file 'NEWS' for a list of major changes in the current release.
See file 'THANKS' for a list of contributors.

Besides those configure options documented in files 'INSTALL' and
'ABOUT-NLS', an extra option may be accepted after './configure':

* Install

** Selecting the default archive format.

The default archive format is GNU, this can be overridden by
presetting DEFAULT_ARCHIVE_FORMAT while configuring. The allowed
values are GNU, V7, OLDGNU, USTAR and POSIX.

** Selecting the default archive device

The default archive device is now 'stdin' on read and 'stdout' on write.
The installer can still override this by presetting 'DEFAULT_ARCHIVE'
in the environment before configuring (the behavior of '-[0-7]' or
'-[0-7]lmh' options in 'tar' are then derived automatically).  Similarly,
'DEFAULT_BLOCKING' can be preset to something else than 20.

** Selecting full pathname of the "rmt" binary.

Previous versions of tar always looked for "rmt" binary in the
directory "/etc/rmt". However, the "rmt" program included
in the distribution was installed under "$prefix/libexec/rmt".
To fix this discrepancy, tar now looks for "$prefix/libexec/rmt".
If you do not want this behavior, specify full path name of
"rmt" binary using DEFAULT_RMT_DIR variable, e.g.:

./configure DEFAULT_RMT_DIR=/etc

If you already have a copy of "rmt" installed and wish to use it
instead of the version supplied with the distribution, use --with-rmt
option:

./configure --with-rmt=/etc/rmt

This will also disable building the included version of rmt.

** Installing backup scripts.

This version of tar is shipped with the shell scripts for producing
incremental backups (dumps) and restoring filesystems from them.
The name of the backup script is "backup". The name of the
restore script is "restore". They are installed in "$prefix/sbin"
directory.

Use option --enable-backup-scripts to compile and install these
scripts.

** '--disable-largefile' omits support for large files, even if the
operating system supports large files.  Typically, large files are
those larger than 2 GB on a 32-bit host.

* Installation hints

Here are a few hints which might help installing 'tar' on some systems.

** gzip and bzip2.

GNU tar uses the gzip and bzip2 programs to read and write compressed
archives.  If you don't have these programs already, you need to
install them.  Their sources can be found at:

ftp://ftp.gnu.org/gnu/gzip/
http://sourceware.cygnus.com/bzip2/

If you see the following symptoms:

   $ tar -xzf file.tar.gz
   gzip: stdin: decompression OK, trailing garbage ignored
   tar: Child returned status 2

then you have encountered a gzip incompatibility that should be fixed
in gzip test version 1.3, which as of this writing is available at
<ftp://alpha.gnu.org/gnu/gzip/>.  You can work around the
incompatibility by using a shell command like
 'gzip -d <file.tar.gz | tar -xzf -'.

** Solaris issues.

GNU tar exercises many features that can cause problems with older GCC
versions.  In particular, GCC 2.8.1 (sparc, -O1 or -O2) is known to
miscompile GNU tar.  No compiler-related problems have been reported
when using GCC 2.95.2 or later.

Recent versions of Solaris tar sport a new -E option to generate
extended headers in an undocumented format.  GNU tar does not
understand these headers.

** Static linking.

Some platform will, by default, prepare a smaller 'tar' executable
which depends on shared libraries.  Since GNU 'tar' may be used for
system-level backups and disaster recovery, installers might prefer to
force static linking, making a bigger 'tar' executable maybe, but able to
work standalone, in situations where shared libraries are not available.
The way to achieve static linking varies between systems.  Set LDFLAGS
to a value from the table below, before configuration (see 'INSTALL').

	Platform	Compiler	LDFLAGS

	(any)		Gnu C		-static
	AIX		(vendor)	-bnso -bI:/lib/syscalls.exp
	HPUX		(vendor)	-Wl,-a,archive
	IRIX		(vendor)	-non_shared
	OSF		(vendor)	-non_shared
	SCO 3.2v5	(vendor)	-dn
	Solaris		(vendor)	-Bstatic
	SunOS		(vendor)	-Bstatic

** Failed tests 'ignfail.sh' or 'incremen.sh'.

In an NFS environment, lack of synchronization between machine clocks
might create difficulties to any tool comparing dates and file time stamps,
like 'tar' in incremental dumps.  This has been a recurrent problem with
GNU Make for the last few years.  We would like a general solution.

** BSD compatibility matters.

Set LIBS to '-lbsd' before configuration (see 'INSTALL') if the linker
complains about 'bsd_ioctl' (Slackware).  Also set CPPFLAGS to
'-I/usr/include/bsd' if <sgtty.h> is not found (Slackware).

** OPENStep 4.2 swap files

Tar cannot read the file /private/vm/swapfile.front (even as root).
This file is not a real file, but some kind of uncompressed view of
the real compressed swap file; there is no reason to back it up, so
the simplest workaround is to avoid tarring this file.

* Special topics

Here are a few special matters about GNU 'tar', not related to build
matters.  See previous section for such.

** File attributes.

About *security*, it is probable that future releases of 'tar' will have
some behavior changed.  There are many pending suggestions to choose from.
Today, extracting an archive not being 'root', 'tar' will restore suid/sgid
bits on files but owned by the extracting user.  'root' automatically gets
a lot of special privileges, '-p' might later become required to get them.

GNU 'tar' does not properly restore symlink attributes.  Various systems
implement flavors of symbolic links showing different behavior and
properties.  We did not successfully sorted all these out yet.  Currently,
the 'lchown' call will be used if available, but that's all.

** POSIX compliance.

GNU 'tar' is able to create archive in the following formats:

  *** The format of UNIX version 7
  *** POSIX.1-1988 format, also known as "ustar format"
  *** POSIX.1-2001 format, also known as "pax format"
  *** Old GNU format (described below)

In addition to those, GNU 'tar' is also able to read archives
produced by 'star' archiver.

A so called 'Old GNU' format is based on an early draft of the
POSIX 1003.1 'ustar' standard which is different from the final
standard. It defines its extensions (such as incremental backups
and handling of the long file names) in a way incompatible with
any existing tar archive format, therefore the use of old GNU
format is strongly discouraged.

Please read the file NEWS for more information about POSIX compliance
and new 'tar' features.

* What's next?

GNU tar will be merged into GNU paxutils: a project containing
several utilities related to creating and handling archives in
various formats. The project will include tar, cpio and pax
utilities.

* Bug reporting.

Send bug reports to <bug-tar@gnu.org>.  A bug report should contain
an adequate description of the problem, your input, what you expected,
what you got, and why this is wrong.  Diffs are welcome, but they only
describe a solution, from which the problem might be uneasy to infer.
If needed, submit actual data files with your report.  Small data files
are preferred.  Big files may sometimes be necessary, but do not send them
to the report address; rather take special arrangement with the maintainer.

Your feedback will help us to make a better and more portable package.
Consider documentation errors as bugs, and report them as such.  If you
develop anything pertaining to 'tar' or have suggestions, let us know
and share your findings by writing to <bug-tar@gnu.org>.

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* Copying

Copyright 1990-2024 Free Software Foundation, Inc.

This file is part of GNU tar.

GNU tar is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.

GNU tar is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program.  If not, see <http://www.gnu.org/licenses/>.

NOTE ON COPYRIGHT YEARS

In copyright notices where the copyright holder is the Free Software
Foundation, then where a range of years appears, this is an inclusive
range that applies to every year in the range.  For example: 2005-2008
represents the years 2005, 2006, 2007, and 2008.
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