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Sergey Poznyakoff
2004-05-08 22:16:17 +00:00
parent ef87ce7d10
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@@ -726,8 +726,10 @@ Performing Backups and Restoring Files
Setting Parameters for Backups and Restoration
* General-Purpose Variables::
* Magnetic Tape Control::
* User Hooks::
* backup-specs example:: An Example Text of @file{Backup-specs}
* Script Syntax:: Syntax for @file{Backup-specs}
Choosing Files and Names for @command{tar}
@@ -780,7 +782,7 @@ Making @command{tar} Archives More Portable
* Portable Names:: Portable Names
* dereference:: Symbolic Links
* old:: Old V7 Archives
* posix:: @sc{posix} archives
* posix:: @acronym{POSIX} archives
* Checksumming:: Checksumming Problems
* Large or Negative Values:: Large files, negative time stamps, etc.
@@ -2778,10 +2780,10 @@ Creates archive in GNU tar 1.13 format. Basically it is the same as
numeric fields.
@item ustar
Creates a POSIX.1-1988 compatible archive.
Creates a @acronym{POSIX.1-1988} compatible archive.
@item posix
Creates a POSIX.1-2001 archive.
Creates a @acronym{POSIX.1-2001 archive}.
@end table
@@ -3043,7 +3045,7 @@ This option does not affect extraction from archives.
@item --pax-option=@var{keyword-list}
This option is meaningful only with POSIX.1-2001 archives
This option is meaningful only with @acronym{POSIX.1-2001} archives
(@FIXME-xref{}). It modifies the way @command{tar} handles the
extended header keywords. @var{Keyword-list} is a comma-separated
list of keyword options, each keyword option taking one of
@@ -3058,8 +3060,8 @@ that it produces any keywords matching the string @var{pattern}.
When used in extract or list mode, this option instructs tar
to ignore any keywords matching the given @var{pattern} in the extended
header records. In both cases, matching is performed using the pattern
matching notation described in POSIX 1003.2, 3.13 (@FIXME-xref{}, see
man 7 glob). For example:
matching notation described in @acronym{POSIX 1003.2}, 3.13 @FIXME-xref{see
man 7 glob}. For example:
@smallexample
--pax-option delete=security.*
@@ -5262,7 +5264,6 @@ placeholder @var{snapshot-file} can be specified, e.g.,
@node Backup Levels
@section Levels of Backups
@UNREVISED
An archive containing all the files in the file system is called a
@dfn{full backup} or @dfn{full dump}. You could insure your data by
@@ -5271,7 +5272,7 @@ substantial amount of archive media and user time, as unchanged files
are daily re-archived.
It is more efficient to do a full dump only occasionally. To back up
files between full dumps, you can a incremental dump. A @dfn{level
files between full dumps, you can use @dfn{incremental dumps}. A @dfn{level
one} dump archives all the files that have changed since the last full
dump.
@@ -5285,81 +5286,89 @@ files changed or created since the last daily backup. (Doing dumps
more than once a day is usually not worth the trouble).
@GNUTAR{} comes with scripts you can use to do full
and level-one dumps. Using scripts (shell programs) to perform
backups and restoration is a convenient and reliable alternative to
typing out file name lists and @command{tar} commands by hand.
and level-one (actually, even level-two and so on) dumps. Using
scripts (shell programs) to perform backups and restoration is a
convenient and reliable alternative to typing out file name lists
and @command{tar} commands by hand.
Before you use these scripts, you need to edit the file
@file{backup-specs}, which specifies parameters used by the backup
scripts and by the restore script. @FIXME{There is no such restore
script!}@FIXME-xref{Script Syntax}Once the backup parameters
are set, you can perform backups or restoration by running the
appropriate script.
scripts and by the restore script. This file is usually located
in @file{/etc/backup} directory. @FIXME-xref{Script Syntax} Once the
backup parameters are set, you can perform backups or restoration by
running the appropriate script.
The name of the restore script is @code{restore}. @FIXME{There is
no such restore script!}The names of the level one and full backup
scripts are, respectively, @code{level-1} and @code{level-0}.
The @code{level-0} script also exists under the name @code{weekly}, and
the @code{level-1} under the name @code{daily}---these additional names
can be changed according to your backup schedule. @FIXME-xref{Scripted
Restoration, for more information on running the restoration script.}
@FIXME-xref{Scripted Backups, for more information on running the
backup scripts.}
The name of the backup script is @code{backup}. The name of the
restore script is @code{restore}. The following sections describe
their use in detail.
@emph{Please Note:} The backup scripts and the restoration scripts are
@emph{Please Note:} The backup and restoration scripts are
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.@FIXME{There is no such restore script!}
@value{xref-incremental}, and @value{xref-listed-incremental},
before making such an attempt.
@FIXME{shorten node names}
it is easier to use the scripts. @value{xref-incremental}, and
@value{xref-listed-incremental}, before making such an attempt.
@node Backup Parameters
@section Setting Parameters for Backups and Restoration
@UNREVISED
The file @file{backup-specs} specifies backup parameters for the
backup and restoration scripts provided with @command{tar}. You must
edit @file{backup-specs} to fit your system configuration and schedule
before using these scripts.
@FIXME{This about backup scripts needs to be written: BS is a shell
script .... thus ... @file{backup-specs} is in shell script syntax.}
Syntactically, @file{backup-specs} is a shell script, containing
mainly variable assignments. However, any valid shell construct
is allowed in this file. Particularly, you may wish to define
functions within that script (e.g. see @code{RESTORE_BEGIN} below).
For more information about shell script syntax, please refer to
@url{http://www.opengroup.org/onlinepubs/009695399/utilities/xcu_chap02.html#ta
g_02, the definition of the Shell Command Language}. See also
@ref{Top,,Bash Features,bashref,Bash Reference Manual}.
@FIXME-xref{Script Syntax, for an explanation of this syntax.}
The shell variables controlling behavior of @code{backup} and
@code{restore} are described in the following subsections.
@FIXME{Whats a parameter .... looked at by the backup scripts
... which will be expecting to find ... now syntax ... value is linked
to lame ... @file{backup-specs} specifies the following parameters:}
@menu
* General-Purpose Variables::
* Magnetic Tape Control::
* User Hooks::
* backup-specs example:: An Example Text of @file{Backup-specs}
@end menu
@table @samp
@item ADMINISTRATOR
The user name of the backup administrator.
@node General-Purpose Variables
@subsection General-Purpose Variables
@item BACKUP_HOUR
The hour at which the backups are done. This can be a number from 0
to 23, or the string @samp{now}.
@defvr {Backup variable} ADMINISTRATOR
The user name of the backup administrator. @code{Backup} scripts
sends a backup report to this address.
@end defvr
@item TAPE_FILE
@defvr {Backup variable} BACKUP_HOUR
The hour at which the backups are done. This can be a number from 0
to 23, or the time specification in form @var{hours}:@var{minutes},
or the string @samp{now}.
This variable is used by @code{backup}. Its value may be overridden
using @option{--time} option (@pxref{Scripted Backups}).
@end defvr
@defvr {Backup variable} TAPE_FILE
The device @command{tar} writes the archive to. This device should be
attached to the host on which the dump scripts are run.
@end defvr
@FIXME{examples for all ...}
@defvr {Backup variable} BLOCKING
@item TAPE_STATUS
The command to use to obtain the status of the archive device,
including error count. On some tape drives there may not be such a
command; in that case, simply use @samp{TAPE_STATUS=false}.
@item BLOCKING
The blocking factor @command{tar} will use when writing the dump archive.
@value{xref-blocking-factor}.
@end defvr
@item BACKUP_DIRS
A list of file systems to be dumped. You can include any directory
name in the list---subdirectories on that file system will be
@defvr {Backup variable} BACKUP_DIRS
A list of file systems to be dumped (for @code{backup}), or restored
(for @code{restore}). You can include any directory
name in the list --- subdirectories on that file system will be
included, regardless of how they may look to other networked machines.
Subdirectories on other file systems will be ignored.
@@ -5373,22 +5382,204 @@ when in that directory on that machine). If the host that contains
the file system does not have this capability, you can specify another
host as long as it can access the file system through NFS.
@item BACKUP_FILES
A list of individual files to be dumped. These should be accessible
from the machine on which the backup script is run.
If the list of file systems is very long you may wish to put it
in a separate file. This file is usually named
@file{/etc/backup/dirs}, but this name may be overridden in
@file{backup-specs} using @code{DIRLIST} variable.
@end defvr
@FIXME{Same file name, be specific. Through NFS ...}
@defvr {Backup variable} DIRLIST
A path to the file containing the list of the filesystems to backup
or restore. By default it is @file{/etc/backup/dirs}.
@end defvr
@defvr {Backup variable} BACKUP_FILES
A list of individual files to be dumped (for @code{backup}), or restored
(for @code{restore}). These should be accessible from the machine on
which the backup script is run.
If the list of file systems is very long you may wish to store it
in a separate file. This file is usually named
@file{/etc/backup/files}, but this name may be overridden in
@file{backup-specs} using @code{FILELIST} variable.
@end defvr
@defvr {Backup variable} FILELIST
A path to the file containing the list of the individual files to backup
or restore. By default it is @file{/etc/backup/files}.
@end defvr
@defvr {Backup variable} RSH
Path to @code{rsh} binary or its equivalent. You may wish to
set it to @code{ssh}, to improve security. In this case you will have
to use public key authentication.
@end defvr
@defvr {Backup variable} RSH_COMMAND
Path to rsh binary on remote mashines. This will be passed via
@option{--rsh-command} option to the remote invocation of @GNUTAR{}.
@end defvr
@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.
@end defvr
@defvr {Backup variable} XLIST
Name of @dfn{exclude file list}. An @dfn{exclude file list} is a file
located on the remote machine and containing the list of files to
be excluded from the backup. Exclude file lists are searched in
/etc/tar-backup directory. A common use for exclude file lists
is to exclude files containing security-sensitive information
(e.g. @file{/etc/shadow} from backups.
This variable affects only @code{backup}.
@end defvr
@defvr {Backup variable} SLEEP_TIME
Time to sleep between dumps of any two successive filesystems
This variable affects only @code{backup}.
@end defvr
@defvr {Backup variable} DUMP_REMIND_SCRIPT
Script to be run when it's time to insert a new tape in for the next
volume. Administrators may want to tailor this script for their site.
If this variable isn't set, @GNUTAR{} will display its built-in prompt
@FIXME-xref{describe it somewhere!}, and will expect confirmation from
the console.
@end defvr
@defvr {Backup variable} SLEEP_MESSAGE
Message to display on the terminal while waiting for dump time. Usually
this will just be some literal text.
@end defvr
@defvr {Backup variable} TAR
Pathname of the @GNUTAR{} executable. If this is not set, backup
scripts will search @command{tar} in the current shell path.
@end defvr
@node Magnetic Tape Control
@subsection Magnetic Tape Control
Backup scripts access tape device using special @dfn{hook functions}.
These functions take a single argument -- the name of the tape
device. Their names are kept in the following variables:
@defvr {Backup variable} MT_BEGIN
The name of @dfn{begin} function. This function is called before
accessing the drive. By default it retensions the tape:
@smallexample
MT_BEGIN=mt_begin
mt_begin() @{
mt -f "$1" retension
@}
@end smallexample
@end defvr
@defvr {Backup variable} MT_REWIND
THe name of @dfn{rewind} function. The default definition is as
follows:
@smallexample
MT_REWIND=mt_rewind
mt_rewind() @{
mt -f "$1" rewind
@}
@end smallexample
@end defvr
@defvr {Backup variable} MT_OFFLINE
The name of the function switching the tape off line. By default
it is defined as follows:
@smallexample
MT_OFFLINE=mt_offline
mt_offline() @{
mt -f "$1" offl
@}
@end smallexample
@end defvr
@defvr {Backup variable} MT_STATUS
The name of the function used to obtain the status of the archive device,
including error count. Default definition:
@smallexample
MT_STATUS=mt_status
mt_status() @{
mt -f "$1" status
@}
@end smallexample
@end defvr
@node User Hooks
@subsection User Hooks
@dfn{User hooks} are shell functions executed before and after
each @command{tar} invocations. Thus, there are @dfn{backup
hooks}, which are executed before and after dumping each file
system, and @dfn{restore hooks}, executed before and
after restoring a file system. Each user hook is a shell function
taking four arguments:
@deffn {User Hook Function} hook @var{level} @var{host} @var{fs} @var{fsname}
The arguments are:
@table @var
@item level
Current backup or restore level.
@item host
Name or IP address of the host machine being dumped or restored.
@item fs
Full path name to the filesystem being dumped or restored.
@item fsname
Filesystem name with directory separators replaced with colons. This
is useful e.g. for creating unique files.
@end table
@end deffn
@menu
* backup-specs example:: An Example Text of @file{Backup-specs}
* Script Syntax:: Syntax for @file{Backup-specs}
@end menu
Following variables keep the names of user hook functions
@defvr {Backup variable} DUMP_BEGIN
Dump begin function. It is executed before dumping the filesystem.
@end defvr
@defvr {Backup variable} DUMP_END
Executed after dumping the filesystem.
@end defvr
@defvr {Backup variable} RESTORE_BEGIN
Executed before restoring the filesystem.
@end defvr
@defvr {Backup variable} RESTORE_END
Executed after restoring the filesystem.
@end defvr
@node backup-specs example
@subsection An Example Text of @file{Backup-specs}
@UNREVISED
The following is the text of @file{backup-specs} as it appears at FSF:
@@ -5398,7 +5589,20 @@ The following is the text of @file{backup-specs} as it appears at FSF:
ADMINISTRATOR=friedman
BACKUP_HOUR=1
TAPE_FILE=/dev/nrsmt0
TAPE_STATUS="mts -t $TAPE_FILE"
# Use @code{ssh} instead of the less secure @code{rsh}
RSH=/usr/bin/ssh
RSH_COMMAND=/usr/bin/ssh
# Override MT_STATUS function:
my_status() @{
mts -t $TAPE_FILE
@}
MT_STATUS=my_status
# Disable MT_OFFLINE function
MT_OFFLINE=:
BLOCKING=124
BACKUP_DIRS="
albert:/fs/fsf
@@ -5420,47 +5624,52 @@ BACKUP_FILES="/com/mailer/aliases /com/mailer/league*[a-z]"
@end smallexample
@node Script Syntax
@subsection Syntax for @file{Backup-specs}
@UNREVISED
@file{backup-specs} is in shell script syntax. The following
conventions should be considered when editing the script:
@FIXME{"conventions?"}
A quoted string is considered to be contiguous, even if it is on more
than one line. Therefore, you cannot include commented-out lines
within a multi-line quoted string. BACKUP_FILES and BACKUP_DIRS are
the two most likely parameters to be multi-line.
A quoted string typically cannot contain wildcards. In
@file{backup-specs}, however, the parameters BACKUP_DIRS and
BACKUP_FILES can contain wildcards.
@node Scripted Backups
@section Using the Backup Scripts
@UNREVISED
The syntax for running a backup script is:
@smallexample
@file{script-name} [@var{time-to-be-run}]
backup --level=@var{level} --time=@var{time}
@end smallexample
where @var{time-to-be-run} can be a specific system time, or can be
@kbd{now}. If you do not specify a time, the script runs at the time
specified in @file{backup-specs}. @FIXME-pxref{Script Syntax}
The @option{level} option requests the dump level. Thus, to produce
a full dump, specify @code{--level=0} (this is the default, so
@option{--level} may be omitted if its value is @code{0}).
@footnote{For backward compatibility, the @code{backup} will also
try to deduce the requested dump level from the name of the
script itself. If the name consists of a string @samp{level-}
followed by a single decimal digit, that digit is taken as
the dump level number. Thus, you may create a link from @code{backup}
to @code{level-1} and then run @code{level-1} whenever you need to
create a level one dump.}
The @option{--time} option determines when should the backup be
run. @var{Time} may take three forms:
@table @asis
@item @var{hh}:@var{mm}
The dump must be run at @var{hh} hours @var{mm} minutes.
@item @var{hh}
The dump must be run at @var{hh} hours
@item now
The dump must be run immediately.
@end table
You should start a script with a tape or disk mounted. Once you
start a script, it prompts you for new tapes or disks as it
needs them. Media volumes don't have to correspond to archive
files---a multi-volume archive can be started in the middle of a
files --- a multi-volume archive can be started in the middle of a
tape that already contains the end of another multi-volume archive.
The @code{restore} script prompts for media by its archive volume,
so to avoid an error message you should keep track of which tape
(or disk) contains which volume of the archive. @FIXME{There is
no such restore script!} @FIXME-xref{Scripted Restoration}
@FIXME{Have file names changed?}
(or disk) contains which volume of the archive (@pxref{Scripted
Restoration}).
The backup scripts write two files on the file system. The first is a
record file in @file{/etc/tar-backup/}, which is used by the scripts
@@ -5474,40 +5683,113 @@ and files dumped, what time the backup was made, and any error
messages that were generated, as well as how much space was left in
the media volume after the last volume of the archive was written.
You should check this log file after every backup. The file name is
@file{log-@var{mmm-ddd-yyyy}-level-1} or
@file{log-@var{mmm-ddd-yyyy}-full}.
@file{log-@var{mmm-ddd-yyyy}-level-@var{n}}, where @var{n} represents
current dump level number.
The script also prints the name of each system being dumped to the
standard output.
Following is the full list of options accepted by @code{backup}
script:
@table @option
@item -l @var{level}
@itemx --level=@var{level}
Do backup level @var{level} (default 0).
@item -f
@itemx --force
Force backup even if today's log file already exists.
@item -v@var{level}
@itemx --verbose[=@var{level}]
Set verbosity level. The higher the level is, the more debugging
information will be output during execution. Devault @var{level}
is 100, which means the highest debugging level.
@item -t @var{start-time}
@itemx --time=@var{start-time}
Wait till @var{time}, then do backup.
@item -h
@itemx --help
Display short help message and exit.
@item -L
@itemx --license
Display program license and exit.
@item -V
@itemx --version
Display program version and exit.
@end table
@node Scripted Restoration
@section Using the Restore Script
@UNREVISED
@ifset PUBLISH
The @command{tar} distribution does not provide restoring scripts.
@end ifset
@ifclear PUBLISH
@quotation
@strong{Warning:} The @GNUTAR{} distribution does @emph{not}
provide any such @code{restore} script yet. This section is only
listed here for documentation maintenance purposes. In any case,
all contents is subject to change as things develop.
@end quotation
@FIXME{A section on non-scripted restore may be a good idea.}
To restore files that were archived using a scripted backup, use the
@code{restore} script. The syntax for the script is:
@code{restore} script. Its usage is quite straightforward. In the
simplest form, invoke @command{restore} without options, it will
then restore all the filesystems and files specified in
@file{backup-specs} (@pxref{General-Purpose Variables,BACKUP_DIRS}).
where ***** are the file systems to restore from, and
***** is a regular expression which specifies which files to
restore. If you specify --all, the script restores all the files
in the file system.
You may select the filesystems (and/or files) to restore by
giving @code{restore} list of @dfn{patterns} in its command
line. For example, running
@smallexample
restore 'albert:*'
@end smallexample
@noindent
will restore all filesystems on the machine @samp{albert}. A more
complicated example:
@smallexample
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.
By default @code{restore} will start restoring files from the lowest
available dump level (usually zero) and will continue through
all available dump levels. There may be situations where such a
thorough restore is not necessary. For example, you may wish to
restore only files from the recent level one backup. To do so,
use @option{--level} option, as shown in the example below:
@smallexample
restore --level=1
@end smallexample
The full list of options accepted by @code{restore} follows:
@table @option
@item -l @var{level}
@itemx --level=@var{level}
Start restoring from the given backup level, instead of the default 0.
@item -v@var{level}
@itemx --verbose[=@var{level}]
Set verbosity level. The higher the level is, the more debugging
information will be output during execution. Devault @var{level}
is 100, which means the highest debugging level.
@item -h
@itemx --help
Display short help message and exit.
@item -L
@itemx --license
Display program license and exit.
@item -V
@itemx --version
Display program version and exit.
@end table
You should start the restore script with the media containing the
first volume of the archive mounted. The script will prompt for other
@@ -5517,10 +5799,6 @@ positioned past the beginning of the archive, the script will rewind
the tape as needed. @FIXME-xref{Media, for a discussion of tape
positioning.}
If you specify @samp{--all} as the @var{files} argument, the
@code{restore} script extracts all the files in the archived file
system into the active file system.
@quotation
@strong{Warning:} The script will delete files from the active file
system if they were not in the file system when the archive was made.
@@ -5529,10 +5807,6 @@ system if they were not in the file system when the archive was made.
@value{xref-incremental}, and @value{ref-listed-incremental},
for an explanation of how the script makes that determination.
@FIXME{this may be an option, not a given}
@end ifclear
@node Choosing
@chapter Choosing Files and Names for @command{tar}
@UNREVISED
@@ -6378,7 +6652,7 @@ The most frequently used formats are (in alphabetical order):
@table @asis
@item gnu
Format used by @GNUTAR{} versions up to 1.13.25. This format derived
from an early POSIX standard, adding some improvements such as
from an early @acronym{POSIX} standard, adding some improvements such as
sparse file handling and incremental archives. Unfortunately these
features were implemented in a way incompatible with other archive
formats.
@@ -6412,7 +6686,7 @@ characters long will not be able to use @GNUTAR{} @value{VERSION} and
Automake prior to 1.9.
@item ustar
Archive format defined by POSIX.1-1988 specification. It stores
Archive format defined by @acronym{POSIX.1-1988} specification. It stores
symbolic ownership information. It is also able to store
special files. However, it imposes several restrictions as well:
@@ -6436,7 +6710,7 @@ implementation. @GNUTAR{} is able to read @samp{star} archives but
currently does not produce them.
@item posix
Archive format defined by POSIX.1-2001 specification. This is the
Archive format defined by @acronym{POSIX.1-2001} specification. This is the
most flexible and feature-rich format. It does not impose any
restrictions on file sizes or filename lengths. This format is quite
recent, so not all tar implementations are able to handle it properly.
@@ -6498,8 +6772,9 @@ contiguous files as such. Let's discuss a few more problems, in turn.
* Portable Names:: Portable Names
* dereference:: Symbolic Links
* old:: Old V7 Archives
* ustar:: Ustar Archives
* gnu:: GNU and old GNU format archives.
* posix:: @sc{posix} archives
* posix:: @acronym{POSIX} archives
* Checksumming:: Checksumming Problems
* Large or Negative Values:: Large files, negative time stamps, etc.
@end menu
@@ -6568,7 +6843,7 @@ contiguous files, and device files, and specifies file ownership by
group and user IDs instead of group and user names.
When updating an archive, do not use @value{op-format-v7}
unless the archive was created with using this option.
unless the archive was created using this option.
In most cases, a @emph{new} format archive can be read by an @emph{old}
@command{tar} program without serious trouble, so this option should
@@ -6576,22 +6851,35 @@ seldom be needed. On the other hand, most modern @command{tar}s are
able to read old format archives, so it might be safer for you to
always use @value{op-format-v7} for your distributions.
@node ustar
@subsection Ustar Archive Format
Archive format defined by @acronym{POSIX}.1-1988 specification is called
@code{ustar}. Although it is more flexible than the V7 format, it
still has many restrictions (@xref{Formats,ustar}, for the detailed
description of @code{ustar} format). Along with V7 format,
@code{ustar} format is a good choice for archives intended to be read
with other implementations of @command{tar}.
To create archive in @code{ustar} format, use @value{op-format-ustar}
option in conjunction with the @value{op-create}.
@node gnu
@subsection @acronym{GNU} and old @GNUTAR{} format
@GNUTAR{} was based on an early draft of the
@sc{posix} 1003.1 @code{ustar} standard. @acronym{GNU} extensions to
@acronym{POSIX} 1003.1 @code{ustar} standard. @acronym{GNU} extensions to
@command{tar}, such as the support for file names longer than 100
characters, use portions of the @command{tar} header record which were
specified in that @sc{posix} draft as unused. Subsequent changes in
@sc{posix} have allocated the same parts of the header record for
specified in that @acronym{POSIX} draft as unused. Subsequent changes in
@acronym{POSIX} have allocated the same parts of the header record for
other purposes. As a result, @GNUTAR{} format is
incompatible with the current @sc{posix} specification, and with
incompatible with the current @acronym{POSIX} specification, and with
@command{tar} programs that follow it.
In the majority of cases, @command{tar} will be configured to create
this format by default. This may change in the future, since we plan
to make @samp{posix} format the default.
this format by default. This will change in the future releases, since
we plan to make @samp{posix} format the default.
To force creation a @GNUTAR{} archive, use option
@value{op-format-gnu}.
@@ -6604,19 +6892,18 @@ or @samp{oldgnu} archive formats. The list of such options follows:
@item @value{op-label}, when used with @value{op-create}.
@item @value{op-incremental}
@item @value{op-multi-volume}
@item @value{op-sparse}
@end itemize
These options will be re-implemented for the @samp{posix} archive
format in the future.
@node posix
@subsection @GNUTAR{} and @sc{posix} @command{tar}
@subsection @GNUTAR{} and @acronym{POSIX} @command{tar}
The version @value{VERSION} of @GNUTAR{} is able
to read and create archives conforming to @sc{posix.1-2001} standard.
to read and create archives conforming to @acronym{POSIX.1-2001} standard.
A @sc{posix} conformant archive will be created if @command{tar}
A @acronym{POSIX} conformant archive will be created if @command{tar}
was given @value{op-format-posix} option.
Notice, that currently @acronym{GNU} extensions are not
allowed with this format. Following is the list of options that
@@ -6626,7 +6913,6 @@ cannot be used with @value{op-format-posix}:
@item @value{op-label}, when used with @value{op-create}.
@item @value{op-incremental}
@item @value{op-multi-volume}
@item @value{op-sparse}
@end itemize
This restriction will disappear in the future versions.
@@ -6638,7 +6924,7 @@ SunOS and HP-UX @command{tar} fail to accept archives created using
@GNUTAR{} and containing non-ASCII file names, that
is, file names having characters with the eight bit set, because they
use signed checksums, while @GNUTAR{} uses unsigned
checksums while creating archives, as per @sc{posix} standards. On
checksums while creating archives, as per @acronym{POSIX} standards. On
reading, @GNUTAR{} computes both checksums and
accept any. It is somewhat worrying that a lot of people may go
around doing backup of their files using faulty (or at least
@@ -6673,24 +6959,24 @@ a @command{tar} able to read the good archives they receive.
@cindex future time stamps
@cindex negative time stamps
@sc{posix} @command{tar} format uses fixed-sized unsigned octal strings
@acronym{POSIX} @command{tar} format uses fixed-sized unsigned octal strings
to represent numeric values. User and group IDs and device major and
minor numbers have unsigned 21-bit representations, and file sizes and
times have unsigned 33-bit representations. @GNUTAR{}
generates @sc{posix} representations when possible, but for values
outside the @sc{posix} range it generates two's-complement base-256
generates @acronym{POSIX} representations when possible, but for values
outside the @acronym{POSIX} range it generates two's-complement base-256
strings: uids, gids, and device numbers have signed 57-bit
representations, and file sizes and times have signed 89-bit
representations. These representations are an extension to @sc{posix}
representations. These representations are an extension to @acronym{POSIX}
@command{tar} format, so they are not universally portable.
The most common portability problems with out-of-range numeric values
are large files and future or negative time stamps.
Portable archives should avoid members of 8 GB or larger, as @sc{posix}
Portable archives should avoid members of 8 GB or larger, as @acronym{POSIX}
@command{tar} format cannot represent them.
Portable archives should avoid time stamps from the future. @sc{posix}
Portable archives should avoid time stamps from the future. @acronym{POSIX}
@command{tar} format can represent time stamps in the range 1970-01-01
00:00:00 through 2242-03-16 12:56:31 @sc{utc}. However, many current
hosts use a signed 32-bit @code{time_t}, or internal time stamp format,
@@ -6698,7 +6984,7 @@ and cannot represent time stamps after 2038-01-19 03:14:07 @sc{utc}; so
portable archives must avoid these time stamps for many years to come.
Portable archives should also avoid time stamps before 1970. These time
stamps are a common @sc{posix} extension but their @code{time_t}
stamps are a common @acronym{POSIX} extension but their @code{time_t}
representations are negative. Many traditional @command{tar}
implementations generate a two's complement representation for negative
time stamps that assumes a signed 32-bit @code{time_t}; hence they
@@ -7816,7 +8102,7 @@ parameter specified this to the operating system.
The Unix man page on @command{tar} was totally confused about this.
When I wrote @code{PD TAR}, I used the historically correct terminology
(@command{tar} writes data records, which are grouped into blocks).
It appears that the bogus terminology made it into @sc{posix} (no surprise
It appears that the bogus terminology made it into @acronym{POSIX} (no surprise
here), and now Fran@,{c}ois has migrated that terminology back
into the source code too.
@end quotation