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Chapter 5. Backup PC hosts using Samba

Michael Zucchi

Original text
School of Computer and Information Science University of South Australia

John R. Jackson

Updates
AMANDA Core Team

Stefan G. Weichinger

XML-conversion;Updates
AMANDA Core Team

Table of Contents

Installation
Setup
Example
Bugs and notes

Note

Refer to http://www.amanda.org/docs/samba.html for the current version of this document.

Installation

Amanda is able to back up Microsoft Windows shared disks by using Samba, a package that implements a SMB client and server for Unix:

http://www.samba.org

Note

This is old stuff and will be (re)moved soon:

Releases from 1.9.18p5 up to 1.9.18p10 logged information in the tar files produced, making them unusable! If you really must use a release prior to Samba 2.0.6, a patch that fixes the problem is available in the Amanda patches page:

http://www.amanda.org/patches/

Amanda no longer supports Samba releases prior to 1.9.18. If you're using Samba from 1.9.18 through 1.9.18p3, make sure you don't set a low logging/debugging level in smb.conf. This flag may prevent estimate sizes from printing correctly and Amanda will report an estimate failure.

This problem may also occur if you have large (>2GB) shares with Samba prior to 2.0.4. In this case, apply samba2-largefs.patch from the Amanda patches page (http://www.amanda.org/patches/).

After building and installing Samba, Amanda must be configured with support for smbclient. Amanda will automatically find smbclient if it is in your PATH when you run configure, or you may add the following argument:

--with-smbclient=/full/path/to/smbclient

Setup

Once Amanda and Samba are installed, the only difference between a Unix client/disk and PC client/share is in how the backup disks are specified in the file disklist. For each PC share, the entry lists the 'samba server' host (where the patched Samba software is installed) and the disk field is the share name. The remaining fields are like any other DLE.

A user must be created on the PC with full access rights (read/write) to the share. Amanda, via the Samba server, will connect to the PC via this user. If the user does not have full access, incremental backups will not work and the whole share will be backed up every time (the archive bits are never reset).

The file /etc/amandapass must be created by hand. It contains share name to user name, password and workgroup mapping. Each line consists of two or three fields, separated by whitespace:

  • Share name followed by optional directory.

    You have to use forward slashes (/), not backslashes (\). This must match the disklist entry exactly (case sensitive). This may be asterisk (*) to match all remaining shares for this Samba server. The first match in the file is used, so specific entries must be listed first. The directory is appended to the share name as full MS network path. Like //thepc/c$/mydir. No blanks are allowed in directory!

  • User name and password.

    Separated by a percent sign (%). See the description of the -U option in the manpage of smbclient. No whitespace is allowed in either the user name or password.

  • Workgroup (optional).

This file must be owned by the Amanda-user, and disallow world access privileges. Blank lines are ignored. A "#" on a line at the start of a field (including start of line) causes the rest of the line to be ignored.

Example

The Amanda client software and (patched) Samba is installed on host "pcserver". A share to be backed up called "backupc" is on PC "thepc". The share will be accessed via PC user "bozo" and password "f00bar" and does not require a workgroup.

The entry in the file disklist is:

pcserver	//thepc/backupc		nocomp-user-gnutar

^ samba installed unix host
                ^ pc host and share name
					^ dumptype must include the tar option

In /etc/amandapass on the machine 'pcserver':

//thepc/backupc		bozo%f00bar

If smbclient requires a workgroup specification (-W), you may add it as a third argument in the line in the file /etc/amandapass :

//thepc/backupc		bozo%f00bar	NTGROUP

This will cause smbclient to be invoked with -W NTGROUP.

An example dumptype in amanda.conf would be:

define dumptype nocomp-user-gnutar {
    program "GNUTAR"
    comment "user partitions dumped with tar and no compression"
    options no-compress
    priority medium
}

Essentially, the entry in disklist is a 'pseudo-disk' which contains all the relevant information needed by smbclient to backup the disk, but in a way that is compatible to Amanda.

amcheck does a quick check to see if smbclient exists and tries to connect to the PC clients. It also checks for the existence and permissions of /etc/amandapass.

Bugs and notes

Samba will not back up open files (such as PAGEFILE.SYS and registry files) nor Access Control List data. Furthermore, at restore time, smbclient is unable to overwrite read-only files. Hence, Amanda+Samba is not a perfect solution for backing up (restoring, actually) system disks.

Samba does not use the Windows Backup API, so configuring the Amanda backup user as a member of group backup on the Windows host is useless. You will probably have to configure it as an Administrator, and make sure it can read and change permission of all files in the share.

It seems impossible to detect when a per-user based login fails, e.g. the username doesn't have sufficient access. It connects but cannot see any files (e.g. backups do nothing). The selfcheck code isn't particularly robust in this area either, so you may get no warnings when a disk isn't being backed up. Just check to see that level 0 dumps are bigger than 64K, otherwise it means the backup was empty.

The estimate and totals are probably a bit off since tar pads to the nearest 512 bytes after each file (I think). Not sure how much of a problem this is.

smbclient only supports excluding a single file from the command line, not a file of patterns like GNU tar. So "exclude" is supported from a dumptype but not "exclude list".

Note

Also the new option "exclude append" is not yet supported with smbclient.

Note

Since Samba-3.0.2a smbclient supports multiple exclusion-patterns. It is one of the "Ongoing Projects" to make use of this in Amanda. Refer to http://www.amanda.org/ongoing.php for details.

The size estimate calculation does not use the same method as the dump, so it may be inaccurate. It also does not support any type of exclusion ("exclude" is ignored). Things are done this way because doing a simulated dump to /dev/null, like other dump programs, would take forever with current implementations of Samba.

If you compile with support for smbclient, GNU-tar support is automatically enabled. If you aren't using the GNU-tar part, you may get warnings about the availability of /usr/local/bin/gtar (or whatever it was compiled with). These may safely be ignored, unless you enable index generation for those filesystems.