unionimap(8)

NAME

unionimap - a tool to manipulate Unionfs inode map files.

SYNOPSIS

unionimap [ -c ] FORWARDMAP
unionimap [ -a FORWARDMAP ] REVERSEMAP PATH
unionimap [ -d ] MAP

DESCRIPTION

unionimap By default, Unionfs generates a different set of

inode numbers each time you mount a file system. Additionally,

the inode numbers used for reading directories is different than

those reported by stat. This can confuse some utilities, and

prevents NFS exports from gracefully handing remounts or server

restarts.

To alleviate these problems, Unionfs supports persistent

inode maps. unionimap is a utility that will generate the inode

map files to be loaded at mount time by Unionfs. An inode map

consists of two main components, a forward map which translates

Unionfs inode numbers to lower-level inode numbers and a lower

level file system, and several reverse maps that are each associ

ated with a single lower-level file system. Note that the maps

are associated with file systems, and not branches. This means

that if you have two branches on the same lower-level file sys

tem, they use only a single reverse map.

OPTIONS

-c create a forward map file. This option takes the

filename of the forward map to create as an argument. This file

name can be the absolute path to the file that you want to create

or you can create it in the local directory and then move it.

-a creates a reverse map file and adds it to a forward

map file. The -a flag itself takes the forward map to add the

new reverse map into. The remaining two arguments are the file

name of the reverse map and then a path to the file system you

wish to create the map for. This will allow the map to have the

appropriate fsid for the file system that you are adding to the

map. If the file system in question does not return a fsid

(i.e., it returns 0 for that value in stat), then one will be

created based on the device's major and minor numbers.

-d dump the contents of either a forward or reverse

map. Specify multiple times for more output. If -d is specified

once, then the header information for the map is printed. If -d

is specified twice, then the contents of the map are also print

ed. For a forward map the contents are keys of a Unionfs inode

number and the value is a pair of file system numbers and lower

inode numbers. For the reverse map, the key is a lower-level in

ode number, and the value is a Unionfs inode number.

USAGE EXAMPLE

unionimap -c /tmp/foo.forward

Create a map named foo.forward in /tmp/

unionimap -a /tmp/foo.forward /tmp/foo.reverse /tmp/

Create a map named foo.reverse in /tmp using /tmp

as the directory to build the fsid from and add it to the forward

map located in /tmp/foo.forward

unionimap -a /tmp/foo.forward /tmp/foo.reverse2 /n/other

Create a map named foo.reverse2 in /tmp using

/n/other as the directory to build the fsid from and add it to

the forward map located in /tmp/foo.forward

unionimap -d /tmp/foo.forward

Display the header contents of /tmp/foo.forward

unionimap -d -d /tmp/foo.forward

Display the header and body contents of

/tmp/foo.forward

AUTHORS

Charles Wright <cwright@cs.sunysb.edu>, David Quigley

<dquigley@ic.sunysb.edu>, Erez Zadok <ezk@cs.sunysb.edu>

SEE ALSO

unionfs(4), http://unionfs.filesystems.org/

Linux September 2005

UNIONIMAP(8)