1 .TH VAC 1
2 .SH NAME
3 vac \- create a vac archive on Venti
4 .SH SYNOPSIS
5 .B vac
6 [
7 .B -mqsv
8 ] [
9 .B -b
10 .I blocksize
11 ] [
12 .B -d
13 .I oldvacfile
14 ] [
15 .B -e
16 .I exclude
17 ] [
18 .B -f
19 .I vacfile
20 ] [
21 .B -i
22 .I name
23 ] [
24 .B -h
25 .I host
26 ]
27 .I file ...
28 .SH DESCRIPTION
29 .I Vac
30 creates an archival copy of Plan 9 file trees on Venti. It can be used
31 to build a simple backup system. One of the unusual properties of Venti is
32 that duplicate blocks are detected and coalesced.  When
33 .I vac
34 is used on a file tree that shares data with an existing archive, the consumption of
35 storage will be approximately equal to an incremental backup.
36 This reduction in storage consumption occurs transparently to the user.
37 .PP
38 As an optimization, the 
39 .B -d
40 and
41 .B -q
42 options, described below, can be used to explicitly create an archive relative to an existing archive.
43 These options do not change the resulting archive generated by
44 .IR vac ,
45 but simply reduce the number of write operations to Venti.
46 .PP
47 The output of
48 .I vac
49 is the hexadecimal representation of the Sha1 fingerprint of the root of the archive, in this format:
50 .IP
51 .EX
52 vac:64daefaecc4df4b5cb48a368b361ef56012a4f46
53 .EE
54 .PP
55 Option to 
56 .I vac
57 are:
58 .TP
59 .BI -b " blocksize
60 Specifies the block size that data will be broken into.
61 The units for the size can be specified by appending
62 .L k
63 to indicate kilobytes.
64 The default is 8k.
65 The size must be in the range
66 of 512 bytes to 52k.
67 .TP
68 .BI -d " oldvacfile
69 Reduce the number of blocks written to Venti by comparing the files to be stored with
70 the contents of an existing
71 .I vac
72 file tree given by
73 .IR oldvacfile .
74 .TP
75 .BI -e " exclude
76 Do not include the file or directory specified by
77 .IR exclude .
78 This option may be repeated multiple times.
79 .TP
80 .BI -f " vacfile
81 The results of 
82 .I vac
83 are place in
84 .IR vacfile ,
85 or the standard output if no file is given.
86 .TP
87 .BI -i " name
88 Include standard input as one of the input files, storing it in the archive
89 with the specified
90 .IR name .
91 .TP
92 .BI -h " host
93 The network address of the Venti server.
94 The default is taken from the environment variable
95 .BR venti .
96 .\" If this variable does not exist, then the default is the
97 .\" metaname 
98 .\" .BR $venti ,
99 .\" which can be configured via
100 .\" .IR ndb (6).
101 .TP
102 .B -m
103 Expand and merge any
104 .I vac
105 archives that are found while reading the input files.  This option is
106 useful for building an archive from a collection of existing archives.  Each archive is inserted
107 into the new archive as if it had been unpacked in the directory in which it was found.  Multiple
108 archives can be unpacked in a single directory and the contents will be merged.  To be detected, the
109 archives must end in
110 .LR .vac .
111 Note, an archive is inserted by simply copying the root fingerprint and does not require
112 the archive to be unpacked.
113 .TP
114 .B -q
115 Increase the performance of the
116 .B -d
117 option by detecting unchanged files based on a match of the files name and other meta data,
118 rather than examining the contents of the files.
119 .TP
120 .B -s
121 Print out various statistics on standard error.
122 .TP
123 .B -v
124 Produce more verbose output on standard error, including the name of the files added to the archive
125 and the vac archives that are expanded and merged.
126 .SH SOURCE
127 .B \*9/src/cmd/vac
128 .SH "SEE ALSO"
129 Plan 9's \fIvacfs\fR(4) and \fIventi\fR(8)