pxtar(1)pxtar(1)Namepxtar - manipulates tape archives
Syntaxpxtar [-c | -r | -t | -u | -x] [-BdFhilmMpsvw] [-number] [bblocks]
[-Cdirectory ...] [-ffile] [-Linputlist] [-Nblocks] [-S blocksb | -S
feet | -S feet @density] [file ...]
Description
The command writes files to or retrieves files from an archive storage
medium or an archive file. The command looks for archives on the
default device (usually tape), unless you specify another device or ar‐
chive file with the -f option.
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 X/Open Portability Guide, Volume
3, XSI Supplementary Definitions, section 18.5.
When writing to an archive, uses a temporary file and maintains in mem‐
ory a table of files with several links. You will receive an error
message if cannot create the temporary file, or if there is not enough
memory available to hold the link tables.
Function Keys
You must supply one of the following five function keys to control the
actions of
-c Creates a new archive and writes the files at the beginning of the
archive.
-r Writes the file at the end of the archive.
-t Lists the files in the order in which they appear in the archive.
Files may appear more than once.
-u Adds file to the end of the archive only if it is not in the ar‐
chive already or if it has been modified since it was written to
the archive.
-x Extracts file from the archive. If you specify a directory,
extracts all files in that directory from the archive. If you do
not specify a file or a directory, extracts all of the files from
the archive. When an archive contains multiple copies of the same
file, extracts only the last one and overwrites all earlier ones.
If you have superuser authority (see the reference page), 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.
Options
The options to 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 sepa‐
rately or be grouped together. Options that take arguments may have
them adjacent to the option letter or as the entire following argument.
The -b, -C, -S, and -f options can accept optional spaces before their
arguments.
-bblocks
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.
The block size is determined automatically when tapes are read
(function keys -x or -t). When archives are updated with the -u
and -r functions, the existing record size is used. The command
writes archives using the specified blocks value only when creat‐
ing new archives with the -c flag.
For output to ordinary files with the -f option, you can save disk
space by using a blocking factor that matches the size of disk
blocks (for example, -b4 for 2048-byte disk blocks). Ordinary
files must be read using the same blocking factor used when they
were created.
-B Forces input and output blocking to 20 blocks per record. This
option was added so that can work across communications channels
where the blocking may not be maintained.
-Cdirectory
Performs a to a directory preceded by -C. This allows multiple
directories not related by a close common parent to be archived
using short relative pathnames. For example, to archive files
from and one might use the following command:
% pxtar c -C/usr/include -C/etc
-d Suppress separate entries for directories, blocks and character
special files, and FIFOs (First In First Out piped processes).
When this option is specified, 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 ar‐
chive. Normally, preserves the directory permission codes and
restores empty directories, special files, and FIFOs with the -x
flag.
-ffile
Uses file as the archive to be read or written. When this option
is not specified, uses a system-dependent default filename of the
form /dev/rmt?h (usually /dev/rmt0h). If the file specified is -
(minus), writes to standard output or reads from standard input.
When writing to standard output, only the -c flag can be used (-r
or -u cannot be used).
-F Checks the file type before archiving. SCCS, RCS, core, error
files, filenames ending in and files will not be archived.
-h Forces to follow symbolic links as if they were normal files or
directories. Normally, does not follow symbolic links.
-i Ignores header checksum errors. The 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
`directory checksum error' when a mismatch occurs. When this
option is specified, 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.
-l Writes error messages to standard output if cannot resolve all of
the links to the files archived. When you do not specify this
option, the system does not display these messages.
-Linputlist
Writes the files listed in the inputlist file to the archive.
inputlist should contain one filename per line. Files and direc‐
tories from inputlist are treated recursively. If you include the
name of a directory in inputlist, command writes the directory to
the archive as well as the files and subdirectories to the ar‐
chive. If you also list files or directories on the command line,
the contents of inputlist are included after has written all the
files or the directories and their subdirectories to the archive.
-m Uses the time of extraction as the modification time. The default
is to preserve the modification time of the files.
-M Instructs not to cross mount points. The default is to cross
mount points.
-Nblocks
Allows to use very large clusters of blocks when it deals with
streaming tape archives. Note, however, that on input, cannot
automatically determine the block size of tapes with very long
block sizes created with this option. In the absence of a
-Nblocks argument, the largest block size that can automatically
determine is 20 blocks.
-p Restores files to their original modes, ignoring the present
umask. "Set user ID" and sticky information will also be restored
when extracted by the superuser.
-s Tries to create a symbolic link if fails in its attempt to link
(regular link) two files.
-S blocksb
-S feet
-S feet @density
Specifies the number of 512-byte blocks 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 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 must be able to determine how many
blocks fit on each volume.
Note that tape drives vary in density capabilities. The density
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.
-v Lists the name of each file as it is processed. With the -t flag,
-v gives more information about the tape entries, including file
sizes, times of last modification, UID, and GID, and permissions.
-w Displays the action to be taken followed by the filename, then
waits for user confirmation. If the response begins with y or Y,
the action is performed; otherwise, the file is ignored.
-number
Uses /dev/rmtnumberh instead of the default. For example, -2 is
the same as -f/dev/rmt2h. The default unit is /dev/rmt0h.
Restrictions
There is no way to ask for any occurrence of a file other than the
last.
There is no recovery from tape errors.
Although anyone can archive special files, only a user with superuser
authority can extract them from an archive.
Do not replace with Although the and commands have much in common, they
are not interchangeable. The command provides compatibility and inter‐
operability with XPG3 systems; is not intended as a replacement for The
command adds tape-label information to a tape archive, so and have dif‐
ferent formats for multiple-volume archives. The command has several
added switches that enable features used in the installation process
and by Substituting the for the causes the command to fail; other com‐
mands may also be affected.
Examples
1. To write file1 and file2 to a new archive on the default tape
drive:
% pxtar-c file1 file2
2. To extract all files that are in the directory from the archive
file on the tape device and use the time of extraction as the
modification time:
% pxtar-xm -f/dev/rmt2 /tmp
3. To create a new archive file that contains file1 and pass the
archive file to the command to be written to the device
% pxtar-cvf - file1 | dd of=/dev/rmt1
4. To display the names of the files in the disk archive file on
the current directory:
% pxtar-vtf out.tar
5. To expand the compressed archive file pass the file to the com‐
mand, and extract all files from the expanded archive file:
% pcat fil.tar.z | pxtar-xvf -
Compatibility Notes
Multi-volume archives created by are not interchangeable with multi-
volume archives created by single-volume archives are interchangeable.
The utility produces archives that follow the format requirements spec‐
ified in the IEEE 1003.1-1988 (POSIX) standard and the X/Open Portabil‐
ity Guide, Issue 3.
Diagnostics
directory checksum error
The -i option was not specified, and a checksum error occurred.
Files
Command path.
Default archive name.
Temporary archive file.
See Alsocat(1), dd(1)pxtar(1)
