X-Git-Url: https://git.dogcows.com/gitweb?a=blobdiff_plain;f=doc%2Ftar.texi;h=78cc8b1f02b36d1206fc4dd98e3c25d4b258c6bc;hb=fd7b257a160a09e4a249d66bf2db0da59db92928;hp=932eef114392c6562770ed949e3d98ccb2233013;hpb=0190e903f539024edfa736bd6f0aead634f0a505;p=chaz%2Ftar diff --git a/doc/tar.texi b/doc/tar.texi index 932eef1..78cc8b1 100644 --- a/doc/tar.texi +++ b/doc/tar.texi @@ -636,13 +636,44 @@ members are named) on the command line (or with @samp{--files-from}) the a file is created with the contents of the archive member. The name of the file is the same as the member name. +Various options cause @code{tar} to extract more than just file +contents, such as the owner, the permissions, the modification date, and +so forth. + +XXX The @samp{--same-permissions} (or @samp{--preserve-permissions}, or @samp{-p}) options cause @code{tar} to cause the new file to have the -same permissions, owner, and so forth, as the original file did when it -was placed in the archive. - -The @samp{--mo - +same permissions as the original file did when it was placed in the +archive. Without this option, the current @code{umask} is used to +affect the permissions. + +When extrating, @code{tar} normally sets the modification time of the +file to the value recorded in the archive. The +@samp{--modification-time} option causes @code{tar} to omit doing this. +XXX + +@section Updating an Archive + +The @samp{--update} (or @samp{-u}) option updates a @code{tar} archive +by comparing the date of the specified archive members against the date +of the file with the same name. If the file has been modified more +recently than the archive member, then the archive member is deleted (as +with @samp{--delete}) and then the file is added to the archive (as with +@samp{--append}). On media where the @samp{--delete} option cannot be +performed (such as magnetic tapes), the @samp{--update} option similarly +fails. + +If no archive members are named (either on the command line or via +@samp{--files-from}), then the entire archive is processed in this +manner. + +@section Comparing Archives Members with Files + +The @samp{--compare} (or @samp{--diff}, or @samp{-d}) option compares +the contents of the specified archive members against the files with the +same names, and reports its findings. If no members are named on the +command line (or through @samp{--files-from}), then the entire archive +is so compared. @chapter Specifying Names to @code{tar} @@ -660,7 +691,10 @@ line, you can put the names into a file, and then use the @samp{--files-from=@var{file-name-list}} (@samp{-T @var{file-name-list}}) option to @code{tar}. Give the name of the file which contains the list as the argument to @samp{--files-from}. The -file names should be separated by newlines in the list. +file names should be separated by newlines in the list. If you give a +single dash as a filename for @samp{--files-from} (that is, you specify +@samp{--files-from=-} or @samp{-T -}), then the filenames are read from +standard input. If you want to specify names that might contain newlines, use the @samp{--null} option. Then, the filenames should be separated by NUL @@ -716,7 +750,7 @@ contents of a single filesystem, because all files named on the command line (or through the @samp{--files-from} option) will always be archived. -@chapter Changing the Names of Members when Archiing +@chapter Changing the Names of Members when Archiving @section Changing Directory @@ -777,6 +811,299 @@ to the archive naming the target of the link. In that way, the However, if you want @code{tar} to actually dump the contents of the target of the symbolic link, then use the @samp{--dereference} option. +@chapter Making @code{tar} More Verbose + +Various options cause @code{tar} to print information as it progresses +in its job. + +The @samp{--verbose} (or @samp{-v}) option causes @code{tar} to print +the name of each archive member or file as it is processed. Since +@samp{--list} already prints the names of the members, @samp{--verbose} +used with @samp{--list} causes @code{tar} to print a longer listing +(reminiscent of @samp{ls -l}) for each member. + +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}.) 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 +the archive, after it has been fully created. + +The @samp{--checkpoint} option prints an occasional message as +@code{tar} reads or writes the archive. It is designed for those who +don't need the more detailed (and voluminous) output of +@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 + +By default, @code{tar} uses an archive file name compiled in when +@code{tar} was built. Usually this refers to some physical tape drive +on the machine. Often, the installer of @code{tar} didn't set the +default to anything meaningful at all. + +As a result, most uses of @code{tar} need to tell @code{tar} where to +find (or create) the archive. The @samp{--file=@var{archive-name}} (or +@samp{-f @var{archive-name}} option selects another file to use as the +archive. + +If the archive file name includes a colon (@samp{:}), then it is assumed +to be a file on another machine. If the archive file is +@samp{@var{user}@@@var{host}:@var{file}}, then @var{file} is used on the +host @var{host}. The remote host is accessed using the @code{rsh} +program, with a username of @var{user}. If the username is omitted +(along with the @samp{@@} sign), then your user name will be used. +(This is the normal @code{rsh} behavior.) It is necessary for the +remote machine, in addition to permitting your @code{rsh} access, to +have the @code{/usr/ucb/rmt} program installed. If you need to use a +file whose name includes a colon, then the remote tape drive behavior +can be inhibited by using the @samp{--force-local} option. + +If the filename you give to @samp{--file} is a single dash (@samp{-}), +then @code{tar} will read the archive from (or write it to) standard +input (or standard output). + +@section Extracting Members to Standard Output + +An archive member in normally extracted into a file with the same name +as the archive member. However, you can use the @samp{--to-stdout} to +cause @code{tar} to write extracted archive members to standard output. +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 +complicated or difficult-to-predict behavior, it is possible to make +serious mistakes. As a result, @code{tar} provides several options that +make observing @code{tar} easier. + +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 +extracting, it will prompt you before each archive member is extracted, +and you can select that member for extraction or pass over to the next. + +The @samp{--verify} option, when using @samp{--create}, causes +@code{tar}, after having finished creating the archive, to go back over +it and compare its contents against the files that were placed in the +archive. + +The @samp{--show-omitted-dirs} option, when reading an archive (with +@samp{--list} or @samp{--extract}, for example), causes a message to be +printed for each directory in the archive which is skipped. This +happens regardless of the reason for skipping: the directory might not +have been named on the command line (implicitly or explicitly), it might +be excluded by the use of the @samp{--exclude} option, or some other +reason. + +@chapter Using Real Tape Drives + +Many complexities surround the use of @code{tar} on tape drives. Since +the creation and manipulation of archives located on magnetic tape was +the original purpose of @code{tar}, it contains many features making +such manipulation easier. + +@section Blocking + +When writing to tapes, @code{tar} writes the contents of the archive in +chunks known as @dfn{blocks}. To change the default blocksize, use the +@samp{--block-size=@var{blocking-factor}} (@samp{-b +@var{blocking-factor}) option. Each block will then be composed of +@var{blocking-factor} records. (Each @code{tar} record is 512 bytes. +@xref{Archive Format}.) Each file written to the archive uses at least +one full block. As a result, using a larger block size can result in +more wasted space for small files. On the other hand, a larger block +size can ofter be read and written much more efficiently. + +Further complicating the problem is that some tape drives ignore the +blocking entirely. For these, a larger block size can still improve +performance (because the software layers above the tape drive still +honor the blocking), but not as dramatically as on tape drives that +honor blocking. + +Wher reading an archive, @code{tar} can usually figure out the block +size on itself. When this is the case, and a non-standard block size +was used when the archive was created, @code{tar} will print a message +about a non-standard blocking factor, and then operate normally. On +some tape devices, however, @code{tar} cannot figure out the block size +itself. On most of those, you can specify a blocking factor (with +@samp{--block-size) larger than the actual blocking factor, and then use +the @samp{--read-full-blocks} option. (If you specify a blocking factor +with @samp{--block-size} and don't use the @samp{--read-full-blocks} +option, then @code{tar} will not attempt to figure out the blocking size +itself.) On some devices, you must always specify the block size +exactly with @samp{--block-size} when reading, because @code{tar} cannot +figure it out. In any case, use @samp{--list} before doing any +extractions to see whether @code{tar} is reading the archive correctly. + +If you use a blocking factor larger than 20, older @code{tar} programs +might not be able to read the archive, so we recommend this as a limit +to use in practice. GNU @code{tar}, however, will support arbitrarily +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 +on the actual tape you are using. In such a case, you can run multiple +@code{tar} commands, but this can be inconvenient, particularly if you +are using options like @samp{--exclude} or dumping entire filesystems. +Therefore, @code{tar} supports multiple tapes automatically. + +Use @samp{--multi-volume} on the command line, and then @code{tar} will, +when it reaches the end of the tape, prompt for another tape, and +continue the archive. Each tape will have an independent archive, and +can be read without needing the other. (As an exception to this, the +file that @code{tar} was archiving when it ran out of tape will usually +be split between the two archives; in this case you need to extract from +the first archive, using @samp{--multi-volume}, and then put in the +second tape when prompted, so @code{tar} can restore both halves of the +file.) + +When prompting for a new tape, @code{tar} accepts any of the following +responses: + +@table @samp +@item ? +Request @code{tar} to explain possible responses +@item q +Request @code{tar} to exit immediately. +@item n @var{file-name} +Request @code{tar} to write the next volume on the file @var{file-name}. +@item ! +Request @code{tar} to run a subshell. +@item y +Request @code{tar} to begin writing the next volume. +@end table + +(You should only type @samp{y} after you have changed the tape; +otherwise @code{tar} will write over the volume it just finished.) + +If you want more elaborate behavior than this, give @code{tar} the +@samp{--info-script=@var{script-name}} option. The file +@var{script-name} is expected to be a program (or shell script) to be +run instead of the normal prompting procedure. When the program +finishes, @code{tar} will immediately begin writing the next volume. +(The behavior of the @samp{n} response to the normal tape-change prompt +is not available if you use @samp{--info-script}.) + +The method @code{tar} uses to detect end of tape is not perfect, and +fails on some operating systems or on some devices. You can use the +@samp{--tape-length=@var{size}} (or @samp{-L @var{size}}) option if +@code{tar} can't detect the end of the tape itself. The @var{size} +argument should be the size of the tape. + +The volume number used by @code{tar} in its tape-change prompt can be +changed; if you give the @samp{--volno-file=@var{file-name}} option, +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 (@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 +error prone, however, and doesn't work at all with @samp{--info-script}. +Therefore, if you give @code{tar} multiple @samp{--file} options, then +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). + +@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 + + + + + + + XXXX MIB XXXX