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* NEWS: New option --atime-preserve=system, which uses O_NOATIME.

Browse Source 
* configure.ac: Prefer AC_CHECK_HEADERS_ONCE to AC_CHECK_HEADERS.
Check for stropts.h and sys/filio.h too, for _FIOSATIME.
* doc/tar.texi: Change "modification time" to "data modification
time", "change time" to "status change time", and "filesystem" to
"file system", so that we use terminology consistent with POSIX.
Use American spacing rather than French for sentence ends.
"non-dependable" -> "undependable".
(Option Summary, Attributes): Explain better the pitfalls of the
--atime-preserve option, and suggest read-only mounts,loopback
mounts, and noatime mounts for older systems.
* doc/value.texi (op-atime-preserve-system): Renamed from
op-atime-preserver-system to fix a misspelling.
* src/common.h (enum atime_preserve): Use lower case for enum values.
* src/compare.c: Don't include utimens.h; no longer needed.
(diff_file): Use set_file_atime rather than utimens; avoid closing
diff_handle until after this, so that we can set the file time stamp
via the file descriptor rather than via its name.
* src/create.c: Don't include utimens.h; no longer needed.
(dump_regular_finish): Remove.  All callers now do its work inline.
(dump_dir): New arg FD.  All callers changed.
Use fdsavedir rather than savedir.
(unknown_file_error): Arg is a const pointer now.
(dump_file0): 2nd arg is a const pointer now.
Treat directories more like files, with respect to --atime-preserve.
For example, also warn if a directory changes while we are dumping it.
Prefer file descriptors to file names when retrieving/setting file
attributes; this saves path-resolution time and allows us to avoid
changing mtime/ctime on Solaris when restoring atime as root.
Use O_DIRECTORY when opening directories, to avoid some race conditions.
Do not reset atime if mtime has changed.  Report an error if
we cannot reset atime.

First cut at adding support for --atime-preserve=system.
* doc/tar.texi (Option Summary): First cut at documenting it.
All other uses of --atime-preserve changed to --atime-preserve=replace.
* doc/value.texi (op-atime-preserve-replace, op-atime-preserver-system):
New.
(op-atime-preserve): Mention METHOD.
* src/common.h (atime_preserve): New enum.
(atime_preserve_option): Now of the enum type rather than bool.
All uses changed.
* src/compare.c (diff_file): Read with O_NOATIME if asked for.
* src/create.c (dump_file0): Read regular and CTG files with O_NOATIME
if asked for.
* src/tar.c (usage): Mention new usage.
(parse_opt): Parse new usage.
This commit is contained in:
Paul Eggert
2005-11-29 19:14:21 +00:00
parent 7b00db5675
commit aa976a5170
12 changed files with 509 additions and 293 deletions
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293
doc/tar.texi
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@@ -227,7 +227,7 @@ Changing How @command{tar} Writes Files
* Keep Newer Files::
* Unlink First::
* Recursive Unlink::
* Modification Times::
* Data Modification Times::
* Setting Access Permissions::
* Writing to Standard Output::
* remove files::
@@ -262,7 +262,7 @@ Choosing Files and Names for @command{tar}
* Wildcards::
* after:: Operating Only on New Files
* recurse:: Descending into Directories
* one:: Crossing Filesystem Boundaries
* one:: Crossing File System Boundaries
Reading Names from a File
@@ -273,7 +273,7 @@ Excluding Some Files
* controlling pattern-patching with exclude::
* problems with exclude::
Crossing Filesystem Boundaries
Crossing File System Boundaries
* directory:: Changing Directory
* absolute:: Absolute File Names
@@ -427,7 +427,7 @@ The @command{tar} program is used to create and manipulate @command{tar}
archives. An @dfn{archive} is a single file which contains the contents
of many files, while still identifying the names of the files, their
owner(s), and so forth. (In addition, archives record access
permissions, user and group, size in bytes, and last modification time.
permissions, user and group, size in bytes, and data modification time.
Some archives also record the file names in each archived directory, as
well as other file and directory information.) You can use @command{tar}
to @dfn{create} a new archive in a specified directory.
@@ -440,14 +440,14 @@ The files inside an archive are called @dfn{members}. Within this
manual, we use the term @dfn{file} to refer only to files accessible in
the normal ways (by @command{ls}, @command{cat}, and so forth), and the term
@dfn{member} to refer only to the members of an archive. Similarly, a
@dfn{file name} is the name of a file, as it resides in the filesystem,
@dfn{file name} is the name of a file, as it resides in the file system,
and a @dfn{member name} is the name of an archive member within the
archive.
@cindex extraction
@cindex unpacking
The term @dfn{extraction} refers to the process of copying an archive
member (or multiple members) into a file in the filesystem. Extracting
member (or multiple members) into a file in the file system. Extracting
all the members of an archive is often called @dfn{extracting the
archive}. The term @dfn{unpack} can also be used to refer to the
extraction of many or all the members of an archive. Extracting an
@@ -511,7 +511,7 @@ projects) together on a disk or a tape. This guards against
accidental destruction of the information in those files.
@GNUTAR{} has special features that allow it to be
used to make incremental and full dumps of all the files in a
filesystem.
file system.
@item Transportation
You can create an archive on one system, transfer it to another system,
@@ -692,7 +692,7 @@ about how Unix-type operating systems work, and you should know how to
use some basic utilities. For example, you should know how to create,
list, copy, rename, edit, and delete files and directories; how to
change between directories; and how to figure out where you are in the
filesystem. You should have some basic understanding of directory
file system. You should have some basic understanding of directory
structure and how files are named according to which directory they are
in. You should understand concepts such as standard output and standard
input, what various definitions of the term ``argument'' mean, and the
@@ -1473,7 +1473,7 @@ earlier (say, @file{blues}), you can extract it from the archive without
changing the archive's structure. It will be identical to the original
file @file{blues} that you deleted. @FIXME{At the time of this
writing, atime and ctime are not restored. Since this is a tutorial
for a beginnig user, it should hardly be mentioned here. Maybe in
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
@@ -1489,7 +1489,7 @@ $ @kbd{tar --extract --file=collection.tar blues}
@noindent
If you list the files in the directory again, you will see that the file
@file{blues} has been restored, with its original permissions, creation
@file{blues} has been restored, with its original permissions, data modification
times, and owner.@FIXME{This is only accidentally true, but not in
general. In most cases, one has to be root for restoring the owner, and
use a special option for restoring permissions. Here, it just happens
@@ -1735,7 +1735,7 @@ option). @value{xref-absolute-names}, for more information about
If you give the name of a directory as either a file name or a member
name, then @command{tar} acts recursively on all the files and directories
beneath that directory. For example, the name @file{/} identifies all
the files in the filesystem to @command{tar}.
the files in the file system to @command{tar}.
The distinction between file names and archive member names is especially
important when shell globbing is used, and sometimes a source of confusion
@@ -2214,16 +2214,51 @@ An exclude pattern must match an initial subsequence of the name's components.
@FIXME-xref{}
@item --atime-preserve
@itemx --atime-preserve=replace
@itemx --atime-preserve=system
Tells @command{tar} to preserve the access time field in a file's inode when
reading it. Due to limitations in the @code{utimes} system call, the
modification time field is also preserved, which may cause problems if
the file is simultaneously being modified by another program.
This option is incompatible with incremental backups, because
preserving the access time involves updating the last-changed time.
Also, this option does not work on files that you do not own,
unless you're root.
@FIXME-xref{}
Attempt to preserve the access time of files when reading them. This
option currently is effective only on files that you own, unless you
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
before reading it, and then restores the access time afterwards. This
may cause problems if other programs are reading the file at the same
time, as the times of their accesses will be lost. On most platforms
restoring the access time also requires @command{tar} to restore the
data modification time too, so this option may also cause problems if
other programs are writing the file at the same time. (Tar attempts
to detect this situation, but cannot do so reliably due to race
conditions.) Worse, on most platforms restoring the access time also
updates the status change time, which means that this option is
incompatible with incremental backups.
@value{op-atime-preserve-system} avoids changing time stamps on files
other than directories, without interfering with time stamp updates
caused by other programs, so it works better with incremental backups.
However, it requires a special @code{O_NOATIME} option from the
underlying operating and file system implementation, and it requires
that searching directories does not update their access times. As of
this writing (November 2005) this works only in a few new Linux
kernels. Worse, there is currently no reliable way to know whether
the features actually work. Sometimes @command{tar} knows for sure
that the features are not working, so it will complain and exit right
away if you try to use @value{op-atime-preserve-system}; but other
times @command{tar} might think that the option is supported when it
is not actually working.
Currently @option{--atime-preserve} with no operand defaults to
@value{op-atime-preserve-replace}, but this may change in the future
as support for @value{op-atime-preserve-system} improves.
@item --backup=@var{backup-type}
@@ -2403,7 +2438,7 @@ archive, which normally signals EOF. @xref{Reading}.
Used to inform @command{tar} that it is working with an old
@acronym{GNU}-format incremental backup archive. It is intended
primarily for backwards compatibility only. @FIXME{incremental and
listed-incremental}.
listed-incremental}.
@item --index-file=@var{file}
@@ -2494,7 +2529,7 @@ in cases when such recognition fails.
When creating an archive, @command{tar} will only add files that have changed
since @var{date}. If @var{date} begins with @samp{/} or @samp{.}, it
is taken to be the name of a file whose last-modified time specifies
is taken to be the name of a file whose data modification time specifies
the date. @FIXME-xref{}
@item --newer-mtime=@var{date}
@@ -2894,8 +2929,8 @@ Displays the total number of bytes written after creating an archive.
@item --touch
@itemx -m
Sets the modification time of extracted files to the extraction time,
rather than the modification time stored in the archive.
Sets the data modification time of extracted files to the extraction time,
rather than the data modification time stored in the archive.
@xref{Writing}.
@item --uncompress
@@ -3538,7 +3573,7 @@ complex. @command{tar} @emph{allows} you to have infinite number of files
with the same name. Some operations treat these same-named members no
differently than any other set of archive members: for example, if you
view an archive with @value{op-list}, you will see all of those members
listed, with their modification times, owners, etc.
listed, with their data modification times, owners, etc.
Other operations don't deal with these members as perfectly as you might
prefer; if you were to use @value{op-extract} to extract the archive,
@@ -4018,7 +4053,7 @@ Do not exit with nonzero on unreadable files or directories.
there's a better way of organizing them.}
The previous chapter showed how to use @value{op-extract} to extract
an archive into the filesystem. Various options cause @command{tar} to
an archive into the file system. Various options cause @command{tar} to
extract more information than just file contents, such as the owner,
the permissions, the modification date, and so forth. This section
presents options to be used with @option{--extract} when certain special
@@ -4113,6 +4148,7 @@ encountered while reading an archive. Use in conjunction with
@subsection Changing How @command{tar} Writes Files
@cindex Overwriting old files, prevention
@cindex Protecting old files
@cindex Data modification times of extracted files
@cindex Modification times of extracted files
@cindex Permissions of extracted files
@cindex Modes of extracted files
@@ -4129,7 +4165,7 @@ encountered while reading an archive. Use in conjunction with
* Keep Newer Files::
* Unlink First::
* Recursive Unlink::
* Modification Times::
* Data Modification Times::
* Setting Access Permissions::
* Writing to Standard Output::
* remove files::
@@ -4161,7 +4197,7 @@ existing files and to follow existing symbolic links when extracting.
Some people argue that @GNUTAR{} should not hesitate
to overwrite files with other files when extracting. When extracting
a @command{tar} archive, they expect to see a faithful copy of the
state of the filesystem when the archive was created. It is debatable
state of the file system when the archive was created. It is debatable
that this would always be a proper behavior. For example, suppose one
has an archive in which @file{usr/local} is a link to
@file{usr/local2}. Since then, maybe the site removed the link and
@@ -4260,22 +4296,22 @@ If you specify the @value{op-recursive-unlink} option,
as far as current permissions will allow it. This could include removal
of the contents of a full directory hierarchy.
@node Modification Times
@unnumberedsubsubsec Setting Modification Times
@node Data Modification Times
@unnumberedsubsubsec Setting Data Modification Times
Normally, @command{tar} sets the modification times of extracted files to
the modification times recorded for the files in the archive, but
Normally, @command{tar} sets the data modification times of extracted
files to the corresponding times recorded for the files in the archive, but
limits the permissions of extracted files by the current @code{umask}
setting.
To set the modification times of extracted files to the time when
To set the data modification times of extracted files to the time when
the files were extracted, use the @value{op-touch} option in
conjunction with @value{op-extract}.
@table @option
@item --touch
@itemx -m
Sets the modification time of extracted archive members to the time
Sets the data modification time of extracted archive members to the time
they were extracted, not the time recorded for them in the archive.
Use in conjunction with @value{op-extract}.
@end table
@@ -4666,7 +4702,7 @@ called @dfn{dumps}.
@cindex corrupted archives
Full dumps should only be made when no other people or programs
are modifying files in the filesystem. If files are modified while
are modifying files in the file system. If files are modified while
@command{tar} is making the backup, they may not be stored properly in
the archive, in which case you won't be able to restore them if you
have to. (Files not being modified are written with no trouble, and do
@@ -4676,18 +4712,18 @@ You will want to use the @value{op-label} option to give the archive a
volume label, so you can tell what this archive is even if the label
falls off the tape, or anything like that.
Unless the filesystem you are dumping is guaranteed to fit on
Unless the file system you are dumping is guaranteed to fit on
one volume, you will need to use the @value{op-multi-volume} option.
Make sure you have enough tapes on hand to complete the backup.
If you want to dump each filesystem separately you will need to use
If you want to dump each file system separately you will need to use
the @value{op-one-file-system} option to prevent @command{tar} from crossing
filesystem boundaries when storing (sub)directories.
file system boundaries when storing (sub)directories.
The @value{op-incremental} (@FIXME-pxref{}) option is not needed,
since this is a complete copy of everything in the filesystem, and a
since this is a complete copy of everything in the file system, and a
full restore from this backup would only be done onto a completely
empty disk.
empty disk.
Unless you are in a hurry, and trust the @command{tar} program (and your
tapes), it is a good idea to use the @value{op-verify} option, to make
@@ -4700,16 +4736,16 @@ capable of being verified, unfortunately.
@section Using @command{tar} to Perform Incremental Dumps
@dfn{Incremental backup} is a special form of @GNUTAR{} archive that
stores additional metadata so that exact state of the filesystem
can be restored when extracting the archive.
stores additional metadata so that exact state of the file system
can be restored when extracting the archive.
@GNUTAR{} currently offers two options for handling incremental
backups: @value{op-listed-incremental} and @value{op-incremental}.
backups: @value{op-listed-incremental} and @value{op-incremental}.
The option @option{--listed-incremental} instructs tar to operate on
an incremental archive with additional metadata stored in a standalone
file, called @dfn{snapshot file}. The purpose of this file is to help
determine what files have been changed, added or deleted since the
file, called a @dfn{snapshot file}. The purpose of this file is to help
determine which files have been changed, added or deleted since the
last backup, so that the next incremental backup will contain only
modified files. The name of the snapshot file is given as an argument
to the option:
@@ -4732,13 +4768,13 @@ $ @kbd{tar --create \
@end smallexample
This will create in @file{archive.1.tar} an incremental backup of
@file{/usr} filesystem, storing additional metadata in the file
the @file{/usr} file system, storing additional metadata in the file
@file{/var/log/usr.snar}. If this file does not exist, it will be
created. The created archive will then be called @dfn{level 0 backup}
(see the next section for more info on backup levels).
created. The created archive will then be a @dfn{level 0 backup};
please see the next section for more on backup levels.
Otherwise, if the file @file{/var/log/usr.snar} exists, it is used to
determine the modified files. In this case only these files will be
Otherwise, if the file @file{/var/log/usr.snar} exists, it
determines which files are modified. In this case only these files will be
stored in the archive. Suppose, for example, that after running the
above command, you delete file @file{/usr/doc/old} and create
directory @file{/usr/local/db} with the following contents:
@@ -4749,7 +4785,7 @@ $ @kbd{ls /usr/local/db}
/usr/local/db/index
@end smallexample
Some time later you create another incremental backup. You will
Some time later you create another incremental backup. You will
then see:
@smallexample
@@ -4765,7 +4801,7 @@ usr/local/db/index
@noindent
The created archive @file{archive.2.tar} will contain only these
three members. This archive is called @dfn{level 1 backup}. Notice,
three members. This archive is called a @dfn{level 1 backup}. Notice
that @file{/var/log/usr.snar} will be updated with the new data, so if
you plan to create more @samp{level 1} backups, it is necessary to
create a working copy of the snapshot file before running
@@ -4781,17 +4817,17 @@ $ @kbd{tar --create \
Incremental dumps depend crucially on time stamps, so the results are
unreliable if you modify a file's time stamps during dumping (e.g.,
with the @option{--atime-preserve} option), or if you set the clock
with the @option{--atime-preserve=replace} option), or if you set the clock
backwards.
Metadata stored in snapshot files include device numbers, which,
obviously is supposed to be a non-volatile value. However, it turns
out that NFS devices have non-dependable values when an automounter
out that NFS devices have undependable values when an automounter
gets in the picture. This can lead to a great deal of spurious
redumping in incremental dumps, so it is somewhat useless to compare
two NFS devices numbers over time. The solution implemented currently
is to considers all NFS devices as being equal when it comes to
comparing directories; this is fairly gross, but there does not seem
comparing directories; this is fairly gross, but there does not seem
to be a better way to go.
Note that incremental archives use @command{tar} extensions and may
@@ -4799,9 +4835,9 @@ not be readable by non-@acronym{GNU} versions of the @command{tar} program.
To extract from the incremental dumps, use
@option{--listed-incremental} together with @option{--extract}
option (@pxref{extracting files}). In this case, @command{tar} does
option (@pxref{extracting files}). In this case, @command{tar} does
not need to access snapshot file, since all the data necessary for
extraction are stored in the archive itself. So, when extracting, you
extraction are stored in the archive itself. So, when extracting, you
can give whatever argument to @option{--listed-incremental}, the usual
practice is to use @option{--listed-incremental=/dev/null}.
Alternatively, you can use @option{--incremental}, which needs no
@@ -4817,10 +4853,10 @@ system that did not exist in their directories when the archive was
created. If you have created several levels of incremental files,
then in order to restore the exact contents the file system had when
the last level was created, you will need to restore from all backups
in turn. Continuing our example, to restore the state of @file{/usr}
in turn. Continuing our example, to restore the state of @file{/usr}
file system, one would do@footnote{Notice, that since both archives
were created withouth @option{-P} option (@pxref{absolute}), these
commands should be run from the root filesystem.}:
commands should be run from the root file system.}:
@smallexample
$ @kbd{tar --extract \
@@ -4832,7 +4868,7 @@ $ @kbd{tar --extract \
@end smallexample
To list the contents of an incremental archive, use @option{--list}
(@pxref{list}), as usual. To obtain more information about the
(@pxref{list}), as usual. To obtain more information about the
archive, use @option{--listed-incremental} or @option{--incremental}
combined with two @option{--verbose} options@footnote{Two
@option{--verbose} options were selected to avoid breaking usual
@@ -4865,7 +4901,7 @@ if the file is present in the archive, @samp{N} if the file is not
included in the archive, or a @samp{D} if the file is a directory (and
is included in the archive).@FIXME-xref{dumpdir format}. Each such
line is terminated by a newline character. The last line is followed
by an additional newline to indicate the end of the data.
by an additional newline to indicate the end of the data.
@anchor{incremental-op}The option @option{--incremental} (@option{-G})
gives the same behavior as @option{--listed-incremental} when used
@@ -4919,7 +4955,7 @@ designed to be used together. While it is possible to restore files by
hand from an archive which was created using a backup script, and to create
an archive by hand which could then be extracted using the restore script,
it is easier to use the scripts. @value{xref-incremental}, before
making such an attempt.
making such an attempt.
@node Backup Parameters
@section Setting Parameters for Backups and Restoration
@@ -5006,7 +5042,7 @@ in a separate file. This file is usually named
@defvr {Backup variable} DIRLIST
A path to the file containing the list of the filesystems to backup
A path to the file containing the list of the file systems to backup
or restore. By default it is @file{/etc/backup/dirs}.
@end defvr
@@ -5050,7 +5086,7 @@ of @GNUTAR{}.
@defvr {Backup variable} VOLNO_FILE
Name of temporary file to hold volume numbers. This needs to be accessible
by all the machines which have filesystems to be dumped.
by all the machines which have file systems to be dumped.
@end defvr
@defvr {Backup variable} XLIST
@@ -5067,7 +5103,7 @@ This variable affects only @code{backup}.
@defvr {Backup variable} SLEEP_TIME
Time to sleep between dumps of any two successive filesystems
Time to sleep between dumps of any two successive file systems
This variable affects only @code{backup}.
@end defvr
@@ -5174,10 +5210,10 @@ Current backup or restore level.
Name or IP address of the host machine being dumped or restored.
@item fs
Full path name to the filesystem being dumped or restored.
Full path name to the file system being dumped or restored.
@item fsname
Filesystem name with directory separators replaced with colons. This
File system name with directory separators replaced with colons. This
is useful, e.g., for creating unique files.
@end table
@end deffn
@@ -5185,19 +5221,19 @@ is useful, e.g., for creating unique files.
Following variables keep the names of user hook functions
@defvr {Backup variable} DUMP_BEGIN
Dump begin function. It is executed before dumping the filesystem.
Dump begin function. It is executed before dumping the file system.
@end defvr
@defvr {Backup variable} DUMP_END
Executed after dumping the filesystem.
Executed after dumping the file system.
@end defvr
@defvr {Backup variable} RESTORE_BEGIN
Executed before restoring the filesystem.
Executed before restoring the file system.
@end defvr
@defvr {Backup variable} RESTORE_END
Executed after restoring the filesystem.
Executed after restoring the file system.
@end defvr
@node backup-specs example
@@ -5353,10 +5389,10 @@ Display program version and exit.
To restore files that were archived using a scripted backup, use the
@code{restore} script. Its usage is quite straightforward. In the
simplest form, invoke @code{restore --all}, it will
then restore all the filesystems and files specified in
then restore all the file systems and files specified in
@file{backup-specs} (@pxref{General-Purpose Variables,BACKUP_DIRS}).
You may select the filesystems (and/or files) to restore by
You may select the file systems (and/or files) to restore by
giving @code{restore} list of @dfn{patterns} in its command
line. For example, running
@@ -5365,7 +5401,7 @@ restore 'albert:*'
@end smallexample
@noindent
will restore all filesystems on the machine @samp{albert}. A more
will restore all file systems on the machine @samp{albert}. A more
complicated example:
@smallexample
@@ -5373,8 +5409,8 @@ restore 'albert:*' '*:/var'
@end smallexample
@noindent
This command will restore all filesystems on the machine @samp{albert}
as well as @file{/var} filesystem on all machines.
This command will restore all file systems on the machine @samp{albert}
as well as @file{/var} file system on all machines.
By default @code{restore} will start restoring files from the lowest
available dump level (usually zero) and will continue through
@@ -5392,7 +5428,7 @@ The full list of options accepted by @code{restore} follows:
@table @option
@item -a
@itemx --all
Restore all filesystems and files specified in @file{backup-specs}
Restore all file systems and files specified in @file{backup-specs}
@item -l @var{level}
@itemx --level=@var{level}
@@ -5431,7 +5467,7 @@ system if they were not in the file system when the archive was made.
@end quotation
@value{xref-incremental}, for an explanation of how the script makes
that determination.
that determination.
@node Choosing
@chapter Choosing Files and Names for @command{tar}
@@ -5453,7 +5489,7 @@ are in specified directories.
* Wildcards::
* after:: Operating Only on New Files
* recurse:: Descending into Directories
* one:: Crossing Filesystem Boundaries
* one:: Crossing File System Boundaries
@end menu
@node file
@@ -5959,7 +5995,7 @@ patterns listed in a file.
@samp{*} or @samp{?} for example, are replaced and expanded into all
existing files matching the given pattern. However, @command{tar} often
uses wildcard patterns for matching (or globbing) archive members instead
of actual files in the filesystem. Wildcard patterns are also used for
of actual files in the file system. Wildcard patterns are also used for
verifying volume labels of @command{tar} archives. This section has the
purpose of explaining wildcard syntax for @command{tar}.
@@ -6009,21 +6045,22 @@ string: excluding a directory also excludes all the files beneath it.
@node after
@section Operating Only on New Files
@cindex Excluding file by age
@cindex Data Modification time, excluding files by
@cindex Modification time, excluding files by
@cindex Age, excluding files by
@UNREVISED
The @value{op-after-date} option causes @command{tar} to only work on files
whose modification or inode-changed times are newer than the @var{date}
whose data modification or status change times are newer than the @var{date}
given. If @var{date} starts with @samp{/} or @samp{.}, it is taken to
be a file name; the last-modified time of that file is used as the date.
be a file name; the data modification time of that file is used as the date.
If you use this option when creating or appending to an archive,
the archive will only include new files. If you use @option{--after-date}
when extracting an archive, @command{tar} will only extract files newer
than the @var{date} you specify.
If you only want @command{tar} to make the date comparison based on
modification of the actual contents of the file (rather than inode
modification of the file's data (rather than status
changes), then use the @value{op-newer-mtime} option.
You may use these options with any operation. Note that these options
@@ -6037,27 +6074,29 @@ deciding whether or not to archive the files.
@itemx -N @var{date}
Only store files newer than @var{date}.
Acts on files only if their modification or inode-changed times are
Acts on files only if their data modification or status change times are
later than @var{date}. Use in conjunction with any operation.
If @var{date} starts with @samp{/} or @samp{.}, it is taken to be a file
name; the last-modified time of that file is used as the date.
name; the data modification time of that file is used as the date.
@item --newer-mtime=@var{date}
Acts like @value{op-after-date}, but only looks at modification times.
Acts like @value{op-after-date}, but only looks at data modification times.
@end table
These options limit @command{tar} to only operating on files which have
been modified after the date specified. A file is considered to have
changed if the contents have been modified, or if the owner,
These options limit @command{tar} to operate only on files which have
been modified after the date specified. A file's status is considered to have
changed if its contents have been modified, or if its owner,
permissions, and so forth, have been changed. (For more information on
how to specify a date, see @ref{Date input formats}; remember that the
entire date argument must be quoted if it contains any spaces.)
Gurus would say that @value{op-after-date} tests both the @code{mtime}
(time the contents of the file were last modified) and @code{ctime}
(time the file's status was last changed: owner, permissions, etc)
fields, while @value{op-newer-mtime} tests only @code{mtime} field.
Gurus would say that @value{op-after-date} tests both the data
modification time (@code{mtime}, the time the contents of the file
were last modified) and the status change time (@code{ctime}, the time
the file's status was last changed: owner, permissions, etc.@:)
fields, while @value{op-newer-mtime} tests only the @code{mtime}
field.
To be precise, @value{op-after-date} checks @emph{both} @code{mtime} and
@code{ctime} and processes the file if either one is more recent than
@@ -6153,7 +6192,7 @@ contents of @file{grape/concord}, but no entries under @file{grape}
other than @file{grape/concord}.
@node one
@section Crossing Filesystem Boundaries
@section Crossing File System Boundaries
@cindex File system boundaries, not crossing
@UNREVISED
@@ -6174,7 +6213,7 @@ archiving. Use in conjunction with any write operation.
The @option{--one-file-system} option causes @command{tar} to modify its
normal behavior in archiving the contents of directories. If a file in
a directory is not on the same filesystem as the directory itself, then
a directory is not on the same file system as the directory itself, then
@command{tar} will not archive that file. If the file is a directory
itself, @command{tar} will not archive anything beneath it; in other words,
@command{tar} will not cross mount points.
@@ -6566,7 +6605,7 @@ than System V's.
Normally, when @command{tar} archives a symbolic link, it writes a
block to the archive naming the target of the link. In that way, the
@command{tar} archive is a faithful record of the filesystem contents.
@command{tar} archive is a faithful record of the file system contents.
@value{op-dereference} is used with @value{op-create}, and causes
@command{tar} to archive the files symbolic links point to, instead of
the links themselves. When this option is used, when @command{tar}
@@ -6930,7 +6969,7 @@ treatment of sparse files may be done automatically with any special
@acronym{GNU} options. For now, it is an option needing to be specified on
the command line with the creation or updating of an archive.
Files in the filesystem occasionally have ``holes.'' A hole in a file
Files in the file system occasionally have ``holes.'' A hole in a file
is a section of the file's contents which was never written. The
contents of a hole read as all zeros. On many operating systems,
actual disk storage is not allocated for holes, but they are counted
@@ -7027,29 +7066,44 @@ get it right.
@section Handling File Attributes
@UNREVISED
When @command{tar} reads files, this causes them to have the access
times updated. To have @command{tar} attempt to set the access times
back to what they were before they were read, use the
@value{op-atime-preserve} option.
When @command{tar} reads files, it updates their access times. To
avoid this, use the @value{op-atime-preserve} option, which can either
reset the access time retroactively or avoid changing it in the first
place.
Handling of file attributes
@table @option
@item --atime-preserve
Preserve access times on files that are read.
This doesn't work for files that
you don't own, unless you're root, and it doesn't interact with
incremental dumps nicely (@pxref{Backups}), and it can set access or
modification times incorrectly if other programs access the file while
@command{tar} is running; but it is good enough for some purposes.
@itemx --atime-preserve=replace
@itemx --atime-preserve=system
Preserve the access times of files that are read. This works only for
files that you own, unless you have superuser privileges.
@value{op-atime-preserve-replace} works on most systems, but it also
restores the data modification time and updates the status change
time. Hence it doesn't interact with incremental dumps nicely
(@pxref{Backups}), and it can set access or data modification times
incorrectly if other programs access the file while @command{tar} is
running.
@value{op-atime-preserve-system} avoids changing the access time in
the first place, if the operating system supports this.
Unfortunately, this may or may not work on any given operating system
or file system. If @command{tar} knows for sure it won't work, it
complains right away.
Currently @option{--atime-preserve} with no operand defaults to
@value{op-atime-preserve-replace}, but this is intended to change to
@value{op-atime-preserve-system} when the latter is better-supported.
@item -m
@itemx --touch
Do not extract file modified time.
Do not extract data modification time.
When this option is used, @command{tar} leaves the modification times
of the files it extracts as the time when the files were extracted,
instead of setting it to the time recorded in the archive.
When this option is used, @command{tar} leaves the data modification times
of the files it extracts as the times when the files were extracted,
instead of setting it to the times recorded in the archive.
This option is meaningless with @value{op-list}.
@@ -7090,7 +7144,7 @@ This is useful in certain circumstances, when restoring a backup from
an emergency floppy with different passwd/group files for example.
It is otherwise impossible to extract files with the right ownerships
if the password file in use during the extraction does not match the
one belonging to the filesystem(s) being extracted. This occurs,
one belonging to the file system(s) being extracted. This occurs,
for example, if you are restoring your files after a major crash and
had booted from an emergency floppy with no password file or put your
disk into another machine to do the restore.
@@ -7244,9 +7298,10 @@ The @code{size} field is the size of the file in bytes; linked files
are archived with this field specified as zero. @FIXME-xref{Modifiers, in
particular the @value{op-incremental} option.}
The @code{mtime} field is the modification time of the file at the time
it was archived. It is the ASCII representation of the octal value of
the last time the file was modified, represented as an integer number of
The @code{mtime} field is the data modification time of the file at
the time it was archived. It is the ASCII representation of the octal
value of the last time the file's contents were modified, represented
as an integer number of
seconds since January 1, 1970, 00:00 Coordinated Universal Time.
The @code{chksum} field is the ASCII representation of the octal value
@@ -7262,8 +7317,8 @@ type, the file will be extracted as if it were a regular file. As this
action occurs, @command{tar} issues a warning to the standard error.
The @code{atime} and @code{ctime} fields are used in making incremental
backups; they store, respectively, the particular file's access time
and last inode-change time.
backups; they store, respectively, the particular file's access and
status change times.
The @code{offset} is used by the @value{op-multi-volume} option, when
making a multi-volume archive. The offset is number of bytes into
@@ -8426,7 +8481,7 @@ failed.
Often you might want to write a large archive, one larger than will fit
on the actual tape you are using. In such a case, you can run multiple
@command{tar} commands, but this can be inconvenient, particularly if you
are using options like @value{op-exclude} or dumping entire filesystems.
are using options like @value{op-exclude} or dumping entire file systems.
Therefore, @command{tar} supports multiple tapes automatically.
Use @value{op-multi-volume} on the command line, and then @command{tar} will,
@@ -8670,7 +8725,7 @@ the first volume file and to decide how to process the rest of the
files. However, it makes no attempt to verify whether the files are
given in order or even if they are valid @command{tar} archives.
It uses @command{dd} and does not filter its standard error, so you
will usually see lots of spurious messages.
will usually see lots of spurious messages.
@FIXME{The script is not installed. Should we install it?}

10
doc/value.texi
View File

@@ -22,7 +22,9 @@
@set xref-append @xref{add}
@set pxref-append @pxref{add}
@set op-atime-preserve @option{--atime-preserve}
@set op-atime-preserve @option{--atime-preserve[=METHOD]}
@set op-atime-preserve-replace @option{--atime-preserve=replace}
@set op-atime-preserve-system @option{--atime-preserve=system}
@set ref-atime-preserve @ref{Attributes}
@set xref-atime-preserve @xref{Attributes}
@set pxref-atime-preserve @pxref{Attributes}
@@ -174,7 +176,7 @@
@set xref-keep-old-files @xref{Keep Old Files}
@set pxref-keep-old-files @pxref{Keep Old Files}
@set op-keep-newer-files @option{--keep-old-files}
@set op-keep-newer-files @option{--keep-old-files}
@set ref-keep-newer-files @ref{Keep Newer Files}
@set xref-keep-newer-files @xref{Keep Newer Files}
@set pxref-keep-newer-files @pxref{Keep Newer Files}
@@ -232,7 +234,7 @@
@set xref-numeric-owner @xref{Attributes}
@set pxref-numeric-owner @pxref{Attributes}
@set op-occurrence @option{--occurrence}
@set op-occurrence @option{--occurrence}
@set ref-occurrence @ref{--occurrence}
@set xref-occurrence @xref{--occurrence}
@set pxref-occurrence @pxref{--occurrence}
@@ -334,7 +336,7 @@
@set xref-starting-file @xref{Scarce}
@set pxref-starting-file @pxref{Scarce}
@set op-strip-components @option{--strip-components}
@set op-strip-components @option{--strip-components}
@set ref-strip-components @ref{--strip-components}
@set xref-strip-components @xref{--strip-components}
@set pxref-strip-components @pxref{--strip-components}