To see the progress of @code{tar} through the archive, the
@samp{--record-number} option prints a message for each record read or
-writted. (@xref{Archive Structure}.)
+writted. (@xref{Archive Structure}.) This option can be very helpful
+when trying to figure out where in the archive an error occurs.
The @samp{--totals} option (which is only meaningful when used with
@samp{--create}) causes @code{tar} to print the total amount written to
@samp{--record-number}, but do want visual confirmation that @code{tar}
is actually making forward progress.
+The @samp{--version} option will generate a message with the version of
+GNU @code{tar} you are using.
+
@chapter Input and Output
@section Changing the Archive Name
If you extract multiple members, they appear on standard output
concatenated, in the order they are found in the archive.
+@section Dealing with Compressed Archives
+
+You can have archives be compressed by using the @samp{--gzip} (or
+@samp{-z}) option. This will arrange for @code{tar} to use the
+@code{gzip} program to be used to compress or uncompress the archive
+wren writing or reading it.
+
+To use the older, obsolete, @code{compress} program, use the
+@samp{--compress} (or @samp{-Z}) option. The GNU Project recommends you
+not use @code{compress}, because there is a patent covering the
+algorithm it uses. Merely by running @code{compress} you could be sued
+for patent infringment.
+
+When using either @samp{--gzip} or @samp{--compress}, @code{tar} does
+not do blocking (@pxref{Blocking}) correctly. Use @samp{--gzip-block}
+or @samp{--compress-block} instead when using real tape drives.
+
@chapter Being More Careful
When using @code{tar} with many options, particularly ones with
serious mistakes. As a result, @code{tar} provides several options that
make observing @code{tar} easier.
-The @samp{--verbose} option (@pxref{Making @code{tar} More Verbose})
-causes @code{tar} to print the name of each file or archive member as it
-is processed.
+The @samp{--verbose} option causes @code{tar} to print the name of each
+file or archive member as it is processed. This and the other options
+which make tar print status information can be useful in monitoring
+@code{tar}. @xref{Making @code{tar} More Verbose}.
If you use @samp{--interactive} (or {@samp--confirm}), then @code{tar}
will ask you for confirmation before each operation. For example, when
large block sizes, limited only by the amount of virtual memory or the
physical characteristics of the tape device.
+If you are writing a compressed archive to tape with @samp{--compress}
+or @samp{--gzip} (@pxref{Input and Output}), @code{tar} will not block
+the archive correctly. This doesn't matter if you are writing the
+archive to a normal file or through a pipe, but if you are writing it to
+a tape drive, then this causes problems. Use @samp{--compress-block} or
+@samp{--gzip-block} instead, to cause @code{tar} to arrange to have
+blocking work correctly.
+
@section Using Multiple Tapes
Often you might want to write a large archive, one larger than will fit
then @var{file-name} should contain a decimal number. That number will
be used as the volume number of the first volume written. When
@code{tar} is finished, it will rewrite the file with the now--current
-volume number. (This does not change the volume number written on a
-tape label; it @emph{only} affects the number used in the prompt.)
+volume number. (This does not change the volume number written on a
+tape label (@pxref{Special Options for Archiving}; it @emph{only}
+affects the number used in the prompt.)
If you want @code{tar} to cycle through a series of tape drives, then
you can use the @samp{n} response to the tape-change prompt. This is
the specified files will be used, in sequence, as the successive volumes
of the archive. Only when the first one in the sequence needs to be
used again will @code{tar} prompt for a tape change (or run the info
-script).
+script).
+
+@section Tape Files
+
+When @code{tar} writes an archive to tape, it creates a single tape
+file. If multiple archives are written to the same tape, one after the
+other, they each get written as separate tape files. When extracting,
+it is necessary to position the tape at the right place before running
+@code{tar}. To do this, use the @code{mt} command. For more
+information on the @code{mt} command and on the organization of tapes
+into a sequence of tape files, see XXX.
+
+@chapter Special Options for Archiving
+
+To give the archive a name which will be recorded in it, use the
+@samp{--label=@var{volume-label}} (or @samp{-V}) option. This will
+write a special record identifying @var{volume-label} as the name of the
+archive to the front of the archive which will be displayed when the
+archive is listed with @samp{--list}. If you are creating a
+multi-volume archive with @samp{--multi-volume} (@pxref{Using Multiple
+Tapes}), then the volume label will have @same{ Volume @var{nnn}}
+appended to the name you give, where @var{nnn} is the number of the
+volume of the archive. (If you use the @samp{--label} option when
+reading an archive, it checks to make sure the label on the tape matches
+the one you give. @xref{Special Options for Archiving}.)
+
+Files in the filesystem 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@c
+disk storage is not allocated for holes, but they are counted in the
+length of the file. If you archive such a file, @code{tar} could create
+an archive longer than the original. To have @code{tar} attempt to
+recognize the holes in a file, use @samp{--sparse}. When you use the
+@samp{--sparse} option, then, for any file using less disk space than
+would be expected from its length, @code{tar} searches the file for
+consecutive stretches of zeros. It then records in the archive for the
+file where the consecutive stretches of zeros are, and only archives the
+``real contents'' of the file. On extraction (using @samp{--sparse} is
+not needed on extraction) any such files have hols created wherever the
+continuous stretches of zeros were found. Thus, if you use
+@samp{--sparse}, @code{tar} archives won't take more space than the
+original.
+
+When @code{tar} reads files, this causes them to have the access times
+updated. To have @code{tar} attempt to set the access times back to
+what they were before they were read, use the @samp{--atime-preserve}
+option. 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{Making Backups}), but it is good enough for some purposes.
+
+@chapter Special Options for Reading Archives
+
+
projects / chaz / tar / commitdiff
