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* doc/tar.texi (Option Summary): Rewrite the

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--atime-preserve=system description in response to Ian Turner's
proposed patch.
* doc/tar.texi (Extracting Specific Files): Remove obsolescent
FIXME.
This commit is contained in:
Paul Eggert
2005-12-01 00:18:05 +00:00
parent f8f4f49011
commit 2edff367d9
2 changed files with 31 additions and 24 deletions
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11
ChangeLog
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@@ -1,3 +1,14 @@
2005-11-30 Paul Eggert <eggert@cs.ucla.edu>
* doc/tar.texi (Option Summary): Rewrite the
--atime-preserve=system description in response to Ian Turner's
proposed patch.
2005-11-30 Ian Turner <ian@zmanda.com>
* doc/tar.texi (Extracting Specific Files): Remove obsolescent
FIXME.
2005-11-29 Paul Eggert <eggert@cs.ucla.edu> 2005-11-29 Paul Eggert <eggert@cs.ucla.edu>
* NEWS: New option --atime-preserve=system, which uses O_NOATIME. * NEWS: New option --atime-preserve=system, which uses O_NOATIME.

44
doc/tar.texi
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@@ -1470,11 +1470,8 @@ To extract specific archive members, give their exact member names as
arguments, as printed by @value{op-list}. If you had mistakenly deleted arguments, as printed by @value{op-list}. If you had mistakenly deleted
one of the files you had placed in the archive @file{collection.tar} one of the files you had placed in the archive @file{collection.tar}
earlier (say, @file{blues}), you can extract it from the archive without earlier (say, @file{blues}), you can extract it from the archive without
changing the archive's structure. It will be identical to the original changing the archive's structure. Its contents will be identical to the
file @file{blues} that you deleted. @FIXME{At the time of this original file @file{blues} that you deleted.
writing, atime and ctime are not restored. Since this is a tutorial
for a beginning user, it should hardly be mentioned here. Maybe in
a footnote? --gray}.
First, make sure you are in the @file{practice} directory, and list the First, make sure you are in the @file{practice} directory, and list the
files in the directory. Now, delete the file, @samp{blues}, and list files in the directory. Now, delete the file, @samp{blues}, and list
@@ -2221,15 +2218,6 @@ Attempt to preserve the access time of files when reading them. This
option currently is effective only on files that you own, unless you option currently is effective only on files that you own, unless you
have superuser privileges. have superuser privileges.
Though this option should work on recent Linux kernel versions, it is
not reliable on other platforms. To preserve the access time reliably
on those platforms, you can mount the file system read-only, or access
the file system via a read-only loopback mount, or use the
@samp{noatime} mount option available on some systems. However,
mounting typically requires superuser privileges and can be a pain to
manage, so the @option{--atime-preserve} option can be useful despite
its glitches on other platforms.
@value{op-atime-preserve-replace} remembers the access time of a file @value{op-atime-preserve-replace} remembers the access time of a file
before reading it, and then restores the access time afterwards. This before reading it, and then restores the access time afterwards. This
may cause problems if other programs are reading the file at the same may cause problems if other programs are reading the file at the same
@@ -2242,24 +2230,32 @@ conditions.) Worse, on most platforms restoring the access time also
updates the status change time, which means that this option is updates the status change time, which means that this option is
incompatible with incremental backups. incompatible with incremental backups.
@value{op-atime-preserve-system} avoids changing time stamps on files @value{op-atime-preserve-system} avoids changing time stamps on files,
other than directories, without interfering with time stamp updates without interfering with time stamp updates
caused by other programs, so it works better with incremental backups. caused by other programs, so it works better with incremental backups.
However, it requires a special @code{O_NOATIME} option from the However, it requires a special @code{O_NOATIME} option from the
underlying operating and file system implementation, and it requires underlying operating and file system implementation, and it also requires
that searching directories does not update their access times. As of that searching directories does not update their access times. As of
this writing (November 2005) this works only in a few new Linux this writing (November 2005) this works only with Linux, and only with
kernels. Worse, there is currently no reliable way to know whether Linux kernels 2.6.8 and later. Worse, there is currently no reliable
the features actually work. Sometimes @command{tar} knows for sure way to know whether this feature actually works. Sometimes
that the features are not working, so it will complain and exit right @command{tar} knows that it does not work, and if you use
away if you try to use @value{op-atime-preserve-system}; but other @value{op-atime-preserve-system} then @command{tar} complains and
times @command{tar} might think that the option is supported when it exits right away. But other times @command{tar} might think that the
is not actually working. option works when it actually does not.
Currently @option{--atime-preserve} with no operand defaults to Currently @option{--atime-preserve} with no operand defaults to
@value{op-atime-preserve-replace}, but this may change in the future @value{op-atime-preserve-replace}, but this may change in the future
as support for @value{op-atime-preserve-system} improves. as support for @value{op-atime-preserve-system} improves.
If your operating system does not support
@value{op-atime-preserve-system}, you might be able to preserve access
times reliably by by using the @command{mount} command. For example,
you can mount the file system read-only, or access the file system via
a read-only loopback mount, or use the @samp{noatime} mount option
available on some systems. However, mounting typically requires
superuser privileges and can be a pain to manage.
@item --backup=@var{backup-type} @item --backup=@var{backup-type}
Rather than deleting files from the file system, @command{tar} will Rather than deleting files from the file system, @command{tar} will