pxtar.1

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.\" Copyright (c) 1990, Digital Equipment Corporation
.\" This material based on work...
.\" Copyright (c) 1990, OPEN SOFTWARE FOUNDATION, INC.
.\" ALL RIGHTS RESERVED
.TH pxtar 1
.SH Name
pxtar \- manipulates tape archives
.SH Syntax
.B pxtar
.RB [ \-c
|
.B \-r
|
.B \-t
|
.B \-u
|
.BR \-x ]
.RB [ \-BdFhilmMpsvw ] 
.RB [ \-\c
.IR number ]
.RB [ b\c
.IR blocks ]
.RB [ \-C\c
.I directory\fP
\&.\&.\&.]
.RB [ \-f\c
.IR file ]
.RB [ \-L\c
.IR inputlist ]
.RB [ \-N\c
.IR blocks ]
.RB [ \-S
.IB blocks b
|
.B \-S 
.I feet
|
.B \-S 
.I feet 
.BI @ density\c
]
.RI [ file
\&.\&.\&.]
.SH Description
.NXR "tape archiver"
.NXR "pxtar command"
.NXR "files" "archival storage"
.NXR "archival storage"
The 
.PN pxtar
command writes files to or retrieves files from an 
archive storage medium or an archive file.
The 
.PN pxtar 
command looks for archives on
the default device (usually tape), unless you
specify another device or archive file with the \fB\-f\fP option.
.PP
Filenames must not be longer than
257 characters and must not contain spaces.  Characters following the
first space are ignored.
Internally, the filename may be split into two pieces to fit into the
header block.
For more details,
see Issue 3 of the 
\fIX/Open\fP\*(TM\fI Portability Guide\fP, \"TITLE_EXEMPT\"
\fIVolume 3\fP, \fIXSI Supplementary 
Definitions\fP, section 18.5. \"TITLE_EXEMPT\"
.PP
When writing to an archive, 
.PN pxtar
uses a temporary file
.Pn ( /tmp/tar* )
and maintains in memory a table of files with
several links.  You will receive an error message if 
.PN pxtar
cannot create the temporary file, or if there is not enough memory
available to hold the link tables.
.SH Function Keys
You must supply one of the following five function keys to
control the actions of 
.PN pxtar :
.TP 5
\fB\-c\fP
Creates a new archive and
writes the files at the beginning of the archive. 
.TP
\fB\-r\fP
Writes the file at the end of the archive.
.TP
\fB\-t\fP
Lists the files in the order in which they appear
in the archive.  Files may appear more than once.
.TP
\fB\-u\fP
Adds file to the end of the
archive only if it is not in the
archive already or if it has been modified since it was written to the
archive.  
.TP
\fB\-x\fP
Extracts file from the archive.  If you specify a directory,
.PN pxtar
extracts all files in that directory from the archive.
If you do not specify a file or a directory,
.PN pxtar
extracts all of the files from the archive.
When an archive contains multiple copies of the same file,
.PN pxtar
extracts only the last one and overwrites all
earlier ones.  If you have superuser authority (see the 
.MS su 1
reference page),
.PN pxtar
creates all files and directories with the same user and
group IDs as on the tape.  If you do not have superuser authority,
the files and directories have your user and group IDs.
.SH Options
The options to 
.PN pxtar
are listed below.
In all cases, a directory argument refers to all the
files and subdirectories, recursively, within that directory.
Options without corresponding arguments may appear separately or be
grouped together.  Options that take arguments may have them adjacent
to the option letter or as the entire following argument.
The \fB\-b\fR, \fB\-C\fR, \fB\-S\fR, and \fB\-f\fR options can accept
optional spaces before their arguments.
.TP 5
\fB\-b\fP\fIblocks\fP
Specifies the number of 512-byte blocks per record.
The default is 20, which is appropriate for tape records.
(The maximum is also 20.)  Due to the size of inter-record gaps, 
tapes written with large blocking factors can hold much more data than
tapes with only one block per record.
.sp .5 
The block size is determined automatically when tapes are read
(function keys \fB\-x\fP or \fB\-t\fP).  When archives are
updated with the \fB\-u\fP and \fB\-r\fP functions, the existing
record size is used.  The 
.PN pxtar
command writes archives using
the specified \fIblocks\fP value only when creating new archives
with the \fB\-c\fP flag.
.sp .5 
For output to ordinary files with the \fB\-f\fP option, you can
save disk space by using a blocking factor that matches the size of disk
blocks (for example, \fB\-b4\fP for 2048-byte disk blocks).
Ordinary files must be read using the same blocking factor used when
they were created.
.TP
\fB\-B\fP
Forces input and output blocking to 20 blocks per record.
This option was added so that 
.PN pxtar
can work across
communications channels where the blocking may not be
maintained.
.TP
\fB\-C\fP\fIdirectory\fR
Performs a 
.PN chdir
to a \fIdirectory\fR preceded by \fB\-C\fP.  This allows
multiple directories not related by a close common parent to be
archived using short relative pathnames.  For example, to
archive files from 
.PN /usr/include
and 
.PN /etc , 
one might use the following command:
.IP
\  % \fBpxtar c \-C/usr/include \-C/etc\fR
.TP
\fB\-d\fP
Suppress separate entries for directories, blocks and character
special files, and FIFOs (First In First Out piped processes).
When this option is specified, 
.PN pxtar
writes only ordinary
files to an archive, and extracts only ordinary files and the directories
required to contain them as determined by the pathnames in the archive.
Normally, 
.PN pxtar
preserves the directory permission codes and restores empty
directories, special files, and FIFOs with the \fB\-x\fP flag.
.TP
\fB\-f\fIfile\fP\fP
Uses \fIfile\fP as the archive to be read or written.  When
this option is not specified,
.PN pxtar
uses a system-dependent default filename of the
form \f(CW/dev/rmt?h\fR
(usually \f(CW/dev/rmt0h\fR).
If the file specified is
\fB\-\fR (minus), 
.PN pxtar
writes to standard output or reads
from standard input.
When writing to standard output, only the \fB\-c\fP
flag can be used (\fB\-r\fP or \fB\-u\fP cannot be used). 
.TP
\fB\-F\fP
Checks the file type before archiving.  SCCS, RCS, core, error
files, filenames ending in 
.PN \&.o
and 
.PN a\&.out
files will
not be archived.
.TP
\fB\-h\fP
Forces 
.PN pxtar
to follow symbolic links
as if they were normal files or directories.  Normally,
.PN pxtar
does not follow symbolic links.
.TP
\fB\-i\fP
Ignores header checksum errors.  The 
.PN pxtar
command
writes a file header containing a checksum for each file
in the archive.  When this option is not specified, the system
verifies the contents of the header blocks by
recomputing the checksum, and aborts with a \fB`directory checksum
error'\fR when a mismatch occurs.  When this option is specified,
.PN pxtar
logs the error and then scans forward until it finds a valid
header block.  This permits restoring files from later volumes of a
multi-volume archive without reading earlier volumes.
.TP
\fB\-l\fP
Writes error messages to standard output if 
.PN pxtar
cannot
resolve all of the links to the files archived.
When you do not specify this option, the system does not display these
messages.
.TP
\fB\-L\fP\fIinputlist\fP
Writes the files listed in the \fIinputlist\fP file to the
archive.  \fIinputlist\fP should contain one filename per line.  Files
and directories from \fIinputlist\fR are treated recursively. If you include
the name of a directory in \fIinputlist\fR, 
.PN pxtar
command writes
the directory to the archive as well as the files and subdirectories
to the archive.  If you also list files or directories on the command 
line, the contents of
\fIinputlist\fP are included after 
.PN pxtar
has written all
the files or the directories and their subdirectories to the archive.
.TP
\fB\-m\fP
Uses the time of extraction as the modification time.
The default is to preserve the modification time of the files.
.TP
\fB\-M\fP
Instructs 
.PN pxtar
not to cross mount points.
The default is to cross mount points.
.TP
\fB\-N\fP\fIblocks\fP
Allows 
.PN pxtar
to use very large clusters of blocks when it
deals with streaming tape archives.  Note, however, that on input,
.PN pxtar
cannot automatically determine the block size of tapes
with very long block sizes created with this option.  
In the absence of a
\fB\-N\fP\fIblocks\fP argument, the largest block size that 
.PN pxtar
can automatically determine is 20 blocks.
.TP
\fB\-p\fP
Restores files to their original modes,
ignoring the present \fIumask\fP.  "Set user ID" and sticky
information will also be restored when extracted by the superuser.
.TP
\fB\-s\fP
Tries to create a symbolic link 
if 
.PN pxtar
fails in its attempt to link (regular link) two files. 
.TP
.PD 0
\fB\-S \fIblocks\fBb\fP
.TP
\fB\-S \fIfeet\fP
.TP
.PD
\fB\-S \fIfeet \fB@\fP\fIdensity\fP
Specifies the number of 512-byte \fIblocks\fP per volume (first
format), independent of the tape blocking factor.  You can also specify
the size of the tape in feet by using the second form, and 
.PN pxtar
assumes a default density.  The third form allows you to
specify both tape length and density.  Feet are assumed to be 11 inches
long to be conservative.  This 
option lets you deal more easily with
multi-volume tape archives, where 
.PN pxtar
must be able to
determine how many blocks fit on each volume.
.sp .5
Note that tape drives vary in density capabilities.  The
\fIdensity\fP argument calculates the amount of data a system can
fit on a tape.  This allows the correct amount of data to be
written to a tape.
.TP
\fB\-v\fP
Lists the name of each file as it is processed.  With
the \fB\-t\fP flag, \fB\-v\fP gives more information
about the tape entries, including file sizes, times of last modification,
UID, and GID, and permissions.
.TP
\fB\-w\fP
Displays the action to be taken followed by the filename, then waits
for user confirmation.  If the response begins with \fBy\fR
or \fBY\fR, the action is performed; otherwise, the file is ignored.
.TP
\fB\-\fInumber\fR
Uses 
\fB/dev/rmt\fInumber\fPh\fR
instead of the default.  For
example, \fB\-2\fR is the same as \fB\-f/dev/rmt2h\fR.
The default unit is 
\fB/dev/rmt0h\fR.
.SH Restrictions
There is no way to ask for any occurrence of a file other than the last.
.PP
There is no recovery from tape errors. 
.PP
Although anyone can archive special files, only a user with
superuser authority can extract them from an archive.
.PP
Do not
replace 
.PN /bin/tar 
with 
.PN pxtar .
Although the 
.PN /bin/tar 
and 
.PN pxtar
commands have much in common, they are
not interchangeable.  The 
.PN pxtar
command provides
compatibility and interoperability with XPG3 systems;  
.PN pxtar 
is not
intended as a replacement for 
.PN /bin/tar .  
The 
.PN /bin/tar
command adds
tape-label information to a tape archive, so 
.PN /bin/tar 
and 
.PN pxtar
have
different formats for multiple-volume archives.  
The 
.PN /bin/tar
command has
several added switches that enable features used in the installation
process and by 
.PN setld .  
Substituting the
.PN pxtar 
for the
.PN /bin/tar
causes the
.PN setld 
command to fail;  other commands may also be affected.  
.SH Examples
.IP \fR1. 
To write \fIfile1\fR and \fIfile2\fR to a new archive
on the default tape drive:
.IP
\  % \fBpxtar \-c \fIfile1 file2\fR
.IP \fR2. 
To extract all files that are in the 
.PN /tmp
directory from
the archive file on the tape device 
.PN /dev/rmt2
and use the time
of extraction as the modification time:
.IP
\  % \fBpxtar \-xm \-f/dev/rmt2 /tmp\fR
.IP \fR3. 
To create a new archive file that contains \fIfile1\fR and
pass the archive file to the 
.PN dd
command to be written to
the device 
.PN /dev/rmt1 :
.IP
\  % \fBpxtar \-cvf \- \fIfile1\fP \(or dd of=/dev/rmt1\fR
.IP \fR4. 
To display the names of the files in the disk archive file
.PN out.tar
on the current directory:
.IP
\  % \fBpxtar \-vtf out\&.tar\fR
.IP \fR5. 
To expand the compressed archive file 
.PN fil.tar.z ,
pass the file to the 
.PN pxtar
command, and extract all files
from the expanded archive file:
.IP
\  % \fBpcat fil\&.tar\&.z \(or pxtar \-xvf \-\fR
.SH Compatibility Notes
Multi-volume archives created by 
.PN pxtar
are not interchangeable
with multi-volume archives created by 
.PN tar ;
single-volume archives are interchangeable.
.PP
The 
.PN pxtar
utility produces archives that follow the format requirements 
specified in the IEEE 1003.1-1988 (\fIPOSIX\fP) standard
and the \fIX/Open Portability Guide, Issue 3\fP.  \"TITLE_EXEMPT\"
.SH Diagnostics
\fBdirectory checksum error\fR 
.br
The \fB\-i\fP option was not specified, and a checksum error occurred.
.SH Files
.PD 0
.TP 20
.PN /usr/bin/pxtar
Command path.
.TP
.PN /dev/rmt0
Default archive name.
.TP
.PD
.PN /tmp/tar*
Temporary archive file.
.SH See Also
cat(1), dd(1)