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VAC(1)                      General Commands Manual                     VAC(1)



NAME
       vac, unvac - create, extract a vac archive on Venti

SYNOPSIS
       vac  [  -mqsv  ] [ -b blocksize ] [ -d oldvacfile ] [ -e exclude ] [ -f
       vacfile ] [ -i name ] [ -h host ] file ...

       unvac [ -Tctv ] [ -h host ] vacfile [ file ...  ]

DESCRIPTION
       Vac creates an archival copy of Plan 9 file trees on Venti. It  can  be
       used  to build a simple backup system. One of the unusual properties of
       Venti is that duplicate blocks are detected and coalesced.  When vac is
       used on a file tree that shares data with an existing archive, the con‐
       sumption of storage will  be  approximately  equal  to  an  incremental
       backup.   This reduction in storage consumption occurs transparently to
       the user.

       As an optimization, the -d and -q options, described below, can be used
       to explicitly create an archive relative to an existing archive.  These
       options do not change the resulting archive generated by vac, but  sim‐
       ply reduce the number of write operations to Venti.

       The output of vac is the hexadecimal representation of the SHA1 finger‐
       print of the root of the archive, in this format:

              vac:64daefaecc4df4b5cb48a368b361ef56012a4f46

       The options to vac are:

       -b blocksize
              Specifies the block size that data will  be  broken  into.   The
              units  for  the  size  can be specified by appending to indicate
              kilobytes.  The default is 8k.  The size must be in the range of
              512 bytes to 52k.

       -d oldvacfile
              Reduce  the  number  of blocks written to Venti by comparing the
              files to be stored with the contents of  an  existing  vac  file
              tree whose score is stored in oldvacfile.

       -e exclude
              Do not include the file or directory specified by exclude.  This
              option may be repeated multiple times.

       -f vacfile
              The results of vac are placed in vacfile, or the standard output
              if no file is given.

       -i name
              Include  standard input as one of the input files, storing it in
              the archive with the specified name.

       -h host
              The network address of the Venti server.  The default  is  taken
              from  the environment variable venti.  If this variable does not
              exist, then the default is the metaname  $venti,  which  can  be
              configured via ndb(6).

       -m     Expand  and  merge any vac archives that are found while reading
              the input files.  This option is useful for building an  archive
              from  a  collection  of  existing archives.  Each archive is in‐
              serted into the new archive as if it had been  unpacked  in  the
              directory  in  which it was found.  Multiple archives can be un‐
              packed in a single directory and the contents  will  be  merged.
              To be detected, the archives must end in Note, an archive is in‐
              serted by simply copying the root fingerprint and does  not  re‐
              quire the archive to be unpacked.

       -q     Increase the performance of the -d option by detecting unchanged
              files based on a match of the files name and  other  meta  data,
              rather than examining the contents of the files.

       -s     Print out various statistics on standard error.

       -v     Produce  more  verbose  output  on standard error, including the
              name of the files added to the archive and the vac archives that
              are expanded and merged.

       Unvac  lists or extracts files stored in the vac archive vacfile, which
       can be either a vac archive string in the format  given  above  or  the
       name of a file containing one.  If file arguments are given, only those
       files or directories will be extracted.  The options are:

       -T     Set the modification time on extracted files to the time  listed
              in the archive.

       -c     Write  extracted  files to standard output instead of creating a
              file.

       -h     as per vac.

       -t     Print a list of the files to standard  output  rather  than  ex‐
              tracting them.

       -v     If  extracting  files, print the name of each file and directory
              to standard error.  If listing files, print metadata in addition
              to the names.

SOURCE
       /sys/src/cmd/vac

SEE ALSO
       vacfs(4), venti(8)



                                                                        VAC(1)