@cindex Labeling an archive
@cindex Labels on the archive media
@cindex Labeling multi-volume archives
-@UNREVISED
@opindex label
To avoid problems caused by misplaced paper labels on the archive
-media, you can include a @dfn{label} entry---an archive member which
-contains the name of the archive---in the archive itself. Use the
+media, you can include a @dfn{label} entry --- an archive member which
+contains the name of the archive --- in the archive itself. Use the
@option{--label=@var{archive-label}} (@option{-V @var{archive-label}})
-option in conjunction with the @option{--create} operation to include
-a label entry in the archive as it is being created.
+option@footnote{Until version 1.10, that option was called
+@option{--volume}, but is not available under that name anymore.} in
+conjunction with the @option{--create} operation to include a label
+entry in the archive as it is being created.
@table @option
@item --label=@var{archive-label}
However, @option{--list} option will cause listing entire
contents of the archive, which may be undesirable (for example, if the
archive is stored on a tape). You can request checking only the volume
-by specifying @option{--test-label} option. This option reads only the
+label by specifying @option{--test-label} option. This option reads only the
first block of an archive, so it can be used with slow storage
devices. For example:
@end group
@end smallexample
- If @option{--test-label} is used with a single command line
-argument, @command{tar} compares the volume label with the
-argument. It exits with code 0 if the two strings match, and with code
-2 otherwise. In this case no output is displayed. For example:
+ If @option{--test-label} is used with one or more command line
+arguments, @command{tar} compares the volume label with each
+argument. It exits with code 0 if a match is found, and with code 1
+otherwise@footnote{Note that @GNUTAR{} versions up to 1.23 indicated
+mismatch with an exit code 2 and printed a spurious diagnostics on
+stderr.}. No output is displayed, unless you also used the
+@option{--verbose} option. For example:
+
+@smallexample
+@group
+$ @kbd{tar --test-label --file=iamanarchive 'iamalabel'}
+@result{} 0
+$ @kbd{tar --test-label --file=iamanarchive 'alabel'}
+@result{} 1
+@end group
+@end smallexample
+
+ When used with the @option{--verbose} option, @command{tar}
+prints the actual volume label (if any), and a verbose diagnostics in
+case of a mismatch:
@smallexample
@group
-$ @kbd{tar --test-label --file=iamanarchive 'iamalable'}
+$ @kbd{tar --test-label --verbose --file=iamanarchive 'iamalabel'}
+iamalabel
@result{} 0
-$ @kbd{tar --test-label --file=iamanarchive 'iamalable' alabel}
+$ @kbd{tar --test-label --verbose --file=iamanarchive 'alabel'}
+iamalabel
+tar: Archive label mismatch
@result{} 1
@end group
@end smallexample
creation time, it sounded logical to equally help the user taking care
of it when the archive is being read.
- The @option{--label} was once called @option{--volume}, but is not
-available under that name anymore.
-
You can also use @option{--label} to get a common information on
all tapes of a series. For having this information different in each
series created through a single script used on a regular basis, just
@end group
@end smallexample
- Also note that each label has its own date and time, which corresponds
-to when @GNUTAR{} initially attempted to write it,
+ Some more notes about volume labels:
+
+@itemize @bullet
+@item Each label has its own date and time, which corresponds
+to the time when @GNUTAR{} initially attempted to write it,
often soon after the operator launches @command{tar} or types the
-carriage return telling that the next tape is ready. Comparing date
-labels does give an idea of tape throughput only if the delays for
-rewinding tapes and the operator switching them were negligible, which
-is usually not the case.
+carriage return telling that the next tape is ready.
+
+@item Comparing date labels to get an idea of tape throughput is
+unreliable. It gives correct results only if the delays for rewinding
+tapes and the operator switching them were negligible, which is
+usually not the case.
+@end itemize
@node verify
@section Verifying Data as It is Stored