Initial revision

[thirdparty/tar.git] / README

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 `PORTS' for various ports of GNU tar to non-Unix systems.
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':

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

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.

For comprehensive modifications to GNU tar, you might need tools beyond
those used in simple installations.  Fully install GNU m4 1.4 first,
and only then, Autoconf 2.13 or later.  Install Perl, then Automake
1.4 or later.  You might need Bison 1.28 or later, and GNU tar itself.
All are available on GNU archive sites, like in
ftp://ftp.gnu.org/pub/gnu/.

Send bug reports to `bug-tar@gnu.org'.  (Beware, old-timers: it is
`@gnu', not `@prep'; and not `bug-gnu-utils' anymore.)  A bug report is
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>.


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 test `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' implements an early draft of the POSIX 1003.1 `ustar' standard
which is different from the final standard.  This will be progressively
corrected over the incoming few years.  Don't be mislead by the mere
existence of the --posix option.  Later releases will become able to
read truly POSIX archives, and also to produce them under option.  (Also,
if you look at the internals, don't take the GNU extensions you see for
granted, as they are planned to change.)  GNU tar 2.0 will produce POSIX
archives by default, but there is a long way before we get there.

* What's next?

In the future we will try to release tar-1.14 as soon as possible and
start merging with paxutils afterwards.  We'll also try to rewrite
some parts of the documentation after paxutils has been merged.