[BackupPC.git] / doc-src / BackupPC.pod

=head1 BackupPC Introduction

This documentation describes BackupPC version __VERSION__,
released on __RELEASEDATE__.

=head2 Overview

BackupPC is a high-performance, enterprise-grade system for backing up
Linux and WinXX PCs, desktops and laptops to a server's disk.  BackupPC
is highly configurable and easy to install and maintain.

Given the ever decreasing cost of disks and raid systems, it is now
practical and cost effective to backup a large number of machines onto a
server's local disk or network storage.  For some sites this might be
the complete backup solution.  For other sites additional permanent
archives could be created by periodically backing up the server to tape.

Features include:

=over 4

=item *

A clever pooling scheme minimizes disk storage and disk I/O.
Identical files across multiple backups of the same or different PC
are stored only once (using hard links), resulting in substantial
savings in disk storage and disk writes.

=item *

Optional compression provides additional reductions in storage
(around 40%).  The CPU impact of compression is low since only
new files (those not already in the pool) need to be compressed.

=item *

A powerful http/cgi user interface allows administrators to view log
files, configuration, current status and allows users to initiate and
cancel backups and browse and restore files from backups.

=item *

No client-side software is needed. On WinXX the standard smb
protocol is used to extract backup data. On linux or unix clients,
rsync or tar (over ssh/rsh/nfs) is used to extract backup data.
Alternatively, rsync can also be used on WinXX (using cygwin),
and Samba could be installed on the linux or unix client to
provide smb shares).

=item *

Flexible restore options.  Single files can be downloaded from
any backup directly from the CGI interface.  Zip or Tar archives
for selected files or directories from any backup can also be
downloaded from the CGI interface.  Finally, direct restore to
the client machine (using smb or tar) for selected files or
directories is also supported from the CGI interface.

=item *

BackupPC supports mobile environments where laptops are only
intermittently connected to the network and have dynamic IP addresses
(DHCP).  Configuration settings allow machines connected via slower WAN
connections (eg: dial up, DSL, cable) to not be backed up, even if they
use the same fixed or dynamic IP address as when they are connected
directly to the LAN.

=item *

Flexible configuration parameters allow multiple backups to be performed
in parallel, specification of which shares to backup, which directories
to backup or not backup, various schedules for full and incremental
backups, schedules for email reminders to users and so on.  Configuration
parameters can be set system-wide or also on a per-PC basis.

=item *

Users are sent periodic email reminders if their PC has not
recently been backed up.  Email content, timing and policies
are configurable.

=item *

BackupPC is Open Source software hosted by SourceForge.

=back

=head2 Backup basics

=over 4

=item Full Backup

A full backup is a complete backup of a share. BackupPC can be configured to
do a full backup at a regular interval (often weekly). BackupPC can also
be configured to keep a certain number of full backups, and to keep
a smaller number of very old full backups.

=item Incremental Backup

An incremental backup is a backup of files that have changed (based on their
modification time) since the last successful full backup.  For SMB and
tar, BackupPC backups all files that have changed since one hour prior to the
start of the last successful full backup.  Rsync is more clever: any files
who attributes have changed (ie: uid, gid, mtime, modes, size) since the
last full are backed up.  Deleted and new files are also detected by
Rsync incrementals (SMB and tar are not able to detect deleted files or
new files whose modification time is prior to the last full dump.

BackupPC can also be configured to keep a certain number of incremental
backups, and to keep a smaller number of very old incremental backups.
(BackupPC does not support multi-level incremental backups, although it
would be easy to do so.)

BackupPC's CGI interface "fills-in" incremental backups based on the 
last full backup, giving every backup a "full" appearance.  This makes
browsing and restoring backups easier.

=item Identical Files

BackupPC pools identical files using hardlinks.  By "identical
files" we mean files with identical contents, not necessary the
same permissions, ownership or modification time.  Two files might
have different permissions, ownership, or modification time but
will still be pooled whenever the contents are identical.  This
is possible since BackupPC stores the file meta-data (permissions,
ownership, and modification time) separately from the file contents.

=item Backup Policy

Based on your site's requirements you need to decide what your backup
policy is.  BackupPC is not designed to provide exact re-imaging of
failed disks.  See L<Limitations|limitations> for more information.
However, the addition of tar transport for linux/unix clients, plus
full support for special file types and unix attributes in v1.4.0
likely means an exact image of a linux/unix file system can be made.

BackupPC saves backups onto disk. Because of pooling you can relatively
economically keep several weeks of old backups. But BackupPC does not
provide permanent storage to tape. Other Open Source applications can do
this by backing up BackupPC's pool directories to tape.

At some sites the disk-based backup will be adequate, without a
secondary tape backup. This system is robust to any single failure: if a
client disk fails or loses files, the BackupPC server can be used to
restore files. If the server disk fails, BackupPC can be restarted on a
fresh file system, and create new backups from the clients. The chance
of the server disk failing can be made very small by spending more money
on increasingly better RAID systems.

At other sites a secondary tape backup will be required. This tape
backup can be done perhaps weekly from the BackupPC pool file system.

One comment: in the US in particular, permanent backups of things like
email are becoming strongly discouraged by lawyers because of discovery
prior to possible litigation.  Using BackupPC without tape backup allows
recent file changes or losses to be restored, but without keeping a
history more than a month or two old (although this doesn't avoid the
problem of old emails languishing in user's email folders forever).

=back

=head2 Resources

=over 4

=item BackupPC home page

The BackupPC Open Source project is hosted on SourceForge.  The
home page can be found at:

    http://backuppc.sourceforge.net

This page has links to the current documentation, the SourceForge
project page and general information.

=item SourceForge project

The SourceForge project page is at:

    http://sourceforge.net/projects/backuppc

This page has links to the current releases of BackupPC.

=item Mail lists

Two BackupPC mailing lists exist for announcements (backuppc-announce)
and reporting information, asking questions, discussing development or
any other topic relevant to BackupPC (backuppc-users).

You are encouraged to subscribe to either the backuppc-announce
or backuppc-users mail list on sourceforge.net at either:

    http://lists.sourceforge.net/lists/listinfo/backuppc-announce
    http://lists.sourceforge.net/lists/listinfo/backuppc-users

The backuppc-announce list is moderated and is used only for
important announcements (eg: new versions).  It is low traffic.
You only need to subscribe to one list: backuppc-users also
receives any messages on backuppc-announce.

To post a message to the backuppc-users list, send an email to

    backuppc-users@lists.sourceforge.net

Do not send subscription requests to this address!

=item Other Programs of Interest

If you want to mirror linux or unix files or directories to a remote server
you should consider rsync, L<http://rsync.samba.org>.  BackupPC uses
rsync as a transport mechanism; if you are already an rsync user you
can think of BackupPC as adding efficient storage (compression and
pooling) and a convenient user interface to rsync.

Unison is a utility that can do two-way, interactive, synchronization.
See L<http://www.cis.upenn.edu/~bcpierce/unison>.

Two popular open source packages that do tape backup are
Amanda (L<http://www.amanda.org>) and
afbackup (L<http://sourceforge.net/projects/afbackup>).
Amanda can also backup WinXX machines to tape using samba.
These packages can be used as back ends to BackupPC to backup the
BackupPC server data to tape.

=back

=head2 Road map

Here are some ideas for new features that might appear in future
releases of BackupPC:

=over 4

=item *

Adding support for rsync as a transport method, in addition to
smb and tar.  This will give big savings in network traffic for
linux/unix clients.  I haven't decided whether to save the pool file
rsync checksums (that would double the number of files in the pool, but
eliminate most server disk reads), or recompute them every time.  I expect
to use native rsync on the client side.  On the server, rsync would
need to understand the compressed file format, the file name mangling
and the attribute files, so I will either have to add features to rsync
or emulate rsync on the server side in perl.

=item *

Adding a trip wire feature for notification when files below certain
directories change.  For example, if you are backing up a DMZ machine,
you could request that you get sent email if any files below /bin,
/sbin or /usr change.

=item *

Resuming incomplete completed full backups.  Useful if a machine
(eg: laptop) is disconnected from the network during a backup,
or if the user manually stops a backup.  This would work by
excluding directories that were already complete.

=item *

More speculative: Storing binary file deltas (in fact, reverse deltas)
for files that have the same name as a previous backup, but that aren't
already in the pool. This will save storage for things like mailbox
files or documents that change slightly between backups.  Running some
benchmarks on a large pool suggests that the potential savings are
around 15-20%, which isn't spectacular, and likely not worth the
implementation effort. The program xdelta (v1) on SourceForge (see
L<http://sourceforge.net/projects/xdelta>) uses an rsync algorithm for
doing efficient binary file deltas.

=back

Comments and suggestions are welcome.

=head2 You can help

BackupPC is free. I work on BackupPC because I enjoy doing it and I like
to contribute to the open source community.

BackupPC already has more than enough features for my own needs.  The
main compensation for continuing to work on BackupPC is knowing that
more and more people find it useful.  So feedback is certainly
appreciated.  Even negative feedback is helpful, for example "We
evaluated BackupPC but didn't use it because it doesn't ...".

Beyond being a satisfied user and telling other people about it, everyone
is encouraged to add links to L<http://backuppc.sourceforge.net> (I'll
see then via Google) or otherwise publicize BackupPC.  Unlike the
commercial products in this space, I have a zero budget (in both
time and money) for marketing, PR and advertising, so it's up to
all of you!

Also, everyone is encouraged to contribute patches, bug reports, feature
and design suggestions, code, and documentation corrections or
improvements.

=head1 Installing BackupPC

=head2 Requirements

BackupPC requires:

=over 4

=item *

A linux, solaris, or unix based server with a substantial amount of free
disk space (see the next section for what that means). The CPU and disk
performance on this server will determine how many simultaneous backups
you can run. You should be able to run 4-8 simultaneous backups on a
moderately configured server.

When BackupPC starts with an empty pool, all the backup data will be
written to the pool on disk. After more backups are done, a higher
percentage of incoming files will already be in the pool. BackupPC is
able to avoid writing to disk new files that are already in the pool.
So over time disk writes will reduce significantly (by perhaps a factor
of 20 or more), since eventually 95% or more of incoming backup files
are typically in the pool. Disk reads from the pool are still needed to
do file compares to verify files are an exact match. So, with a mature
pool, if a relatively fast client generates data at say 1MB/sec, and you
run 4 simultaneous backups, there will be an average server disk load of
about 4MB/sec reads and 0.2MB/sec writes (assuming 95% of the incoming
files are in the pool). These rates will be perhaps 40% lower if
compression is on.

=item *

Perl version 5.6.0 or later. BackupPC has been tested with
version 5.6.0 and 5.6.1. If you don't have perl, please see
L<http://www.cpan.org>.

=item *

Perl modules Compress::Zlib, Archive::Zip and Rsync.  Try "perldoc
Compress::Zlib" and "perldoc Archive::Zip" to see if you have these
modules.  If not, fetch them from L<http://www.cpan.org> and see the
instructions below for how to build and install them.

The Rsync module is available from L<http://backuppc.sourceforge.net>.
You'll need to install the Rsync module if you want to use Rsync as
a transport method.

=item *

If you are using smb to backup WinXX machines you need smbclient and
nmblookup from the samba package.  You will also need nmblookup if
you are backing up linux/unix DHCP machines.  See L<http://www.samba.org>.
Version >= 2.2.0 of Samba is required (smbclient's tar feature in
2.0.8 and prior has bugs for file path lengths around 100 characters
and generates bad output when file lengths change during the backup).

See L<http://www.samba.org> for source and binaries.  It's pretty easy to
fetch and compile samba, and just grab smbclient and nmblookup, without
doing the installation. Alternatively, L<http://www.samba.org> has binary
distributions for most platforms.

=item *

If you are using tar to backup linux/unix machines you should have version
1.13.7 at a minimum, with version 1.13.20 or higher recommended.  Use
"tar --version" to check your version.  Various GNU mirrors have the newest
versions of tar, see for example L<http://www.funet.fi/pub/gnu/alpha/gnu/tar>.
As of July 2002 the latest versons is 1.13.25.

=item *

If you are using rsync to backup linux/unix machines you should have
version 2.5.5 on each client machine.  See L<http://rsync.samba.org>.
Use "rsync --version" to check your version.

For BackupPC to use Rsync you will also need to install the perl Rsync
module, which is available from L<http://backuppc.sourceforge.net>.

=item *

The Apache web server, see L<http://www.apache.org>, preferably built
with mod_perl support.

=back

=head2 How much disk space do I need?

Here's one real example for an environment that is backing up 65 laptops
with compression off. Each full backup averages 3.2GB. Each incremental
backup averages about 0.2GB. Storing one full backup and two incremental
backups per laptop is around 240GB of raw data. But because of the
pooling of identical files, only 87GB is used.  This is without
compression.

Another example, with compression on: backing up 95 laptops, where
each backup averages 3.6GB and each incremental averages about 0.3GB.
Keeping three weekly full backups, and six incrementals is around
1200GB of raw data.  Because of pooling and compression, only 150GB
is needed.

Here's a rule of thumb. Add up the C drive usage of all the machines you
want to backup (210GB in the first example above). This is a rough
minimum space estimate that should allow a couple of full backups and at
least half a dozen incremental backups per machine. If compression is on
you can reduce the storage requirements by maybe 30-40%.  Add some margin
in case you add more machines or decide to keep more old backups.

Your actual mileage will depend upon the types of clients, operating
systems and applications you have. The more uniform the clients and
applications the bigger the benefit from pooling common files.

For example, the Eudora email tool stores each mail folder in a separate
file, and attachments are extracted as separate files. So in the sadly
common case of a large attachment emailed to many recipients, Eudora
will extract the attachment into a new file. When these machines are
backed up, only one copy of the file will be stored on the server, even
though the file appears in many different full or incremental backups. In
this sense Eudora is a "friendly" application from the point of view of
backup storage requirements.

An example at the other end of the spectrum is Outlook. Everything
(email bodies, attachments, calendar, contact lists) is stored in a
single file, which often becomes huge. Any change to this file requires
a separate copy of the file to be saved during backup. Outlook is even
more troublesome, since it keeps this file locked all the time, so it
cannot be read by smbclient whenever Outlook is running.  See the
L<Limitations|limitations> section for more discussion of this problem.

=head2 Step 1: Getting BackupPC

Download the latest version from L<http://backuppc.sourceforge.net>.

=head2 Step 2: Installing the distribution

First off, to enable compression, you will need to install Compress::Zlib
from L<http://www.cpan.org>.  It is optional, but strongly recommended.
To support restore via Zip archives you will need to install
Archive::Zip, also from L<http://www.cpan.org>.  You can run
"perldoc Compress::Zlib" to see if this module is installed.
Finally, you will need the Rsync module.  To build and install these
packages you should run these commands:

    tar zxvf Archive-Zip-1.01.tar.gz
    cd Archive-Zip-1.01
    perl Makefile.PL
    make
    make test
    make install

Now let's move onto BackupPC itself.  After fetching
BackupPC-__VERSION__.tar.gz, run these commands as root:

    tar zxf BackupPC-__VERSION__.tar.gz
    cd BackupPC-__VERSION__
    perl configure.pl

You will be prompted for the full paths of various executables, and
you will be prompted for the following information:

=over 4

=item BackupPC User

It is best if BackupPC runs as a special user, eg backuppc, that has
limited privileges. It is preferred that backuppc belongs to a system
administrator group so that sys admin members can browse backuppc files,
edit the configuration files and so on. Although configurable, the
default settings leave group read permission on pool files, so make
sure the BackupPC user's group is chosen restrictively.

On this installation, this is __BACKUPPCUSER__.

=item Data Directory

You need to decide where to put the data directory, below which
all the BackupPC data is stored.  This needs to be a big file system.

On this installation, this is __TOPDIR__.

=item Install Directory

You should decide where the BackupPC scripts, libraries and documentation
should be installed, eg: /opt/local/BackupPC.

On this installation, this is __INSTALLDIR__.

=item CGI bin Directory

You should decide where the BackupPC CGI script resides.  This will
usually below Apache's cgi-bin directory.

On this installation, this is __CGIDIR__.

=item Apache image directory

A directory where BackupPC's images are stored so that Apache can
serve them.  This should be somewhere under Apache's DocumentRoot
directory.

=back

=head2 Step 3: Setting up config.pl

After running configure.pl, browse through the config file,
__INSTALLDIR__/conf/config.pl, and make sure all the default settings
are correct. In particular, you will need to decide whether to use
smb or tar transport (or whether to set it on a per-PC basis),
set the smb share password (if using smb), set the backup policies
and modify the email message headers and bodies.

BackupPC needs to know the smb share user name and password for each PC
that uses smb (ie: all the WinXX clients).  The user name is specified
in $Conf{SmbShareUserName}. There are four ways to tell BackupPC the smb
share password:

=over 4

=item *

As an environment variable BPC_SMB_PASSWD set before BackupPC starts.
If you start BackupPC manually the BPC_SMB_PASSWD variable must be set
manually first.  For backward compatability for v1.5.0 and prior, the
environment variable PASSWD can be used if BPC_SMB_PASSWD is not set.
Warning: on some systems it is possible to see environment variables of
running processes.

=item *

Alternatively the BPC_SMB_PASSWD setting can be included in
/etc/init.d/backuppc, in which case you must make sure this file
is not world (other) readable.

=item *

As a configuration variable $Conf{SmbSharePasswd} in
__TOPDIR__/conf/config.pl.  If you put the password
here you must make sure this file is not world (other) readable.

=item *

As a configuration variable $Conf{SmbSharePasswd} in the per-PC
configuration file, __TOPDIR__/pc/$host/config.pl. You will have to
use this option if the smb share password is different for each host.
If you put the password here you must make sure this file is not
world (other) readable.

=back

Placement and protection of the smb share password is a possible
security risk, so please double-check the file and directory
permissions.  In a future version there might be support for
encryption of this password, but a private key will still have to
be stored in a protected place.  Suggestions are welcome.

=head2 Step 4: Setting up the hosts file

The file __TOPDIR__/conf/hosts contains the list of clients to backup.
BackupPC reads this file in three cases:

=over 4

=item *

Upon startup.

=item *

When BackupPC is sent a HUP (-1) signal.  Assuming you installed the
init.d script, you can also do this with "/etc/init.d/backuppc reload".

=item *

When the modification time of the hosts file changes.  BackupPC
checks the modification time once during each regular wakeup.

=back

Whenever you change the hosts file (to add or remove a host) you can
either do a kill -HUP BackupPC_pid or simply wait until the next regular
wakeup period.

Each line in the hosts file contains three fields, separated
by white space:

=over 4

=item Host name

If this host is a static IP address this must the machine's IP host name
(ie: something that can be looked up using nslookup or DNS). If this is
a host with a dynamic IP address (ie: DHCP flag is 1) then the host
name must be the netbios name of the machine.  The host name should
be in lower case.

=item DHCP flag

Set to 0 if this host has a static IP address (meaning it can be looked
up by name in the DNS).  If the host's IP address is dynamic (eg, it is
assigned by DHCP) then set this flag to 1.

The hosts with dhcp = 1 are backed up as follows.  If you have
configured a DHCP address pool ($Conf{DHCPAddressRanges}) then
BackupPC will check the NetBIOS name of each machine in the
range.  Any hosts that have a valid NetBIOS name (ie: matching
an entry in the hosts file) will be backed up.

=item User name

This should be the unix login/email name of the user who "owns" or uses
this machine. This is the user who will be sent email about this
machine, and this user will have permission to stop/start/browse/restore
backups for this host.  Leave this blank if no specific person should
receive email or be allowed to stop/start/browse/restore backups
for this host.  Administrators will still have full permissions.

=back

The first non-comment line of the hosts file is special: it contains
the names of the columns and should not be edited.

Here's a simple example of a hosts file:

    host        dhcp    user
    farside     0       craig
    larson      1       gary

The range of DHCP addresses to search is specified in
$Conf{DHCPAddressRanges}.

=head2 Step 5: Client Setup

Two methods for getting backup data from a client are
supported: smb and tar. Smb is the preferred method for WinXX clients
and tar is preferred method for linux/unix clients.

The transfer method is set using the $Conf{XferMethod} configuration
setting. If you have a mixed environment (ie: you will use smb for some
clients and tar for others), you will need to pick the most common
choice for $Conf{XferMethod} for the main config.pl file, and then
override it in the per-PC config file for those hosts that will use
the other method.  (Or you could run two completely separate instances
of BackupPC, with different data directories, one for WinXX and the
other for linux/unix, but then common files between the different
machine types will duplicated.)

Here are some brief client setup notes:

=over 4

=item WinXX

The preferred setup for WinXX clients is to set $Conf{XferMethod} to "smb".

You need to create shares for the data you want to backup.
Open "My Computer", right click on the drive (eg: C), and
select "Sharing..." (or select "Properties" and select the
"Sharing" tab).  In this dialog box you can enable sharing,
select the share name and permissions.

If this machine uses DHCP you will also need to make sure the
NetBios name is set.  Go to Control Panel|System|Network Identification
(on Win2K) or Control Panel|System|Computer Name (on WinXP).
Also, you should go to Control Panel|Network Connections|Local Area
Connection|Properties|Internet Protocol (TCP/IP)|Properties|Advanced|WINS
and verify that NetBios is not disabled.

As an alternative to setting $Conf{XferMethod} to "smb" (using
smbclient) for WinXX clients, you can use an smb network filesystem (eg:
ksmbfs or similar) on your linux/unix server to mount the share,
and then set $Conf{XferMethod} to "tar" (use tar on the network
mounted file system).

Also, to make sure that file names with 8-bit characters are correctly
transferred by smbclient you should add this to samba's smb.conf file:

    [global]
        # Accept the windows charset
        client code page = 850
        character set = ISO8859-1

This setting should work for western europe.  
See L<http://www.oreilly.com/catalog/samba/chapter/book/ch08_03.html>
for more information about settings for other languages.

=item Linux/Unix

The preferred setup for linux/unix clients is to set $Conf{XferMethod}
to "tar".

You can use either smb or tar for linux/unix machines. Smb requires that
the Samba server (smbd) be run to provide the shares. Since the smb
protocol can't represent special files like symbolic links and fifos,
tar is the recommended transport method for linux/unix machines.
(In fact, by default samba makes symbolic links look like the file or
directory that they point to, so you could get an infinite loop if a
symbolic link points to the current or parent directory. If you really
need to use Samba shares for linux/unix backups you should turn off the
"follow symlinks" samba config setting. See the smb.conf manual page.)

The rest of this section describes the tar setup.

You must have GNU tar on the client machine.  Use "tar --version"
or "gtar --version" to verify.  The version should be at least
1.13.7, and 1.13.20 or greater is recommended.

For linux/unix machines you should no backup "/proc".  This directory
contains a variety of files that look like regular files but they are
special files that don't need to be backed up (eg: /proc/kcore is a
regular file that contains physical memory).  See $Conf{BackupFilesExclude}.
It is safe to back up /dev since it contains mostly character-special
and block-special files, which are correctly handed by BackupPC
(eg: backing up /dev/hda5 just saves the block-special file information,
not the contents of the disk).

Next you should decide whether to run tar over ssh, rsh or nfs. Ssh is
the preferred method. Rsh is not secure and therefore not recommended.
Nfs will work, but you need to make sure that the BackupPC user (running
on the server) has sufficient permissions to read all the files below
the nfs mount.

Ssh allows BackupPC to run as a privileged user on the client (eg:
root), since it needs sufficient permissions to read all the backup
files. Ssh is setup so that BackupPC on the server (an otherwise low
privileged user) can ssh as root on the client, without being prompted
for a password. There are two common versions of ssh: v1 and v2. Here
are some instructions for one way to setup ssh v2:

=over 4

=item Key generation

As root on the client machine, use ssh2-keygen to generate a
public/private key pair, without a pass-phrase:

    ssh-keygen2 -t rsa -P

This will save the public key in /.ssh2/id_rsa_1024_a.pub and the private
key in /.ssh2/id_rsa_1024_a.

=item Identification

Create the identification file /.ssh2/identification:

    echo "IdKey id_rsa_1024_a" > /.ssh2/identification

=item BackupPC setup

Repeat the above steps for the BackupPC user (__BACKUPPCUSER__) on the server.
Rename the key files to recognizable names, eg:

    ssh-keygen2 -t rsa -P
    mv ~/.ssh2/id_rsa_1024_a.pub ~/.ssh2/BackupPC_id_rsa_1024_a.pub
    mv ~/.ssh2/id_rsa_1024_a     ~/.ssh2/BackupPC_id_rsa_1024_a
    echo "IdKey BackupPC_id_rsa_1024_a" > ~/.ssh2/identification

Based on your ssh2 configuration, you might also need to turn off
StrictHostKeyChecking and PasswordAuthentication:

    touch ~/.ssh2/ssh2_config
    echo "StrictHostKeyChecking ask" >> ~/.ssh2/ssh2_config
    echo "PasswordAuthentication no" >> ~/.ssh2/ssh2_config

=item Key exchange

To allow BackupPC to ssh to the client as root, you need to place
BackupPC's public key into root's authorized list on the client.
Copy BackupPC's public key (BackupPC_id_rsa_1024_a.pub) to the
/.ssh2 directory on the client.  Add the following line to the
/.ssh2/authorization file on the client (as root):

    touch /.ssh2/authorization
    echo "Key BackupPC_id_rsa_1024_a.pub" >> /.ssh2/authorization

=item Fix permissions

You will probably need to make sure that all the files
in /.ssh2 have no group or other read/write permission:

    chmod -R go-rwx /.ssh2

You should do the same thing for the BackupPC user on the server.

=item Testing

As the BackupPC user on the server, verify that this command:

    ssh2 -l root clientHostName whoami

prints

    root

You might be prompted the first time to accept the client's host key and
you might be prompted for root's password on the client.  Make sure that
this command runs cleanly with no prompts after the first time.  You
might need to check /etc/hosts.equiv on the client.  Look at the
man pages for more information.  The "-v" option to ssh2 is a good way
to get detailed information about what fails.

=item ssh version 1 instructions

The concept is identical and the steps are similar, but the specific
commands and file names are slightly different.

First, run ssh-keygen on the client (as root) and server (as the BackupPC
user) and simply hit enter when prompted for the pass-phrase:

    ssh-keygen

This will save the public key in /.ssh/identity.pub and the private
key in /.ssh/identity.

Next, append BackupPC's ~/.ssh/identity.pub (from the server) to root's
/.ssh/authorized_keys file on the client.  It's a single long line that
you can cut-and-paste with an editor (make sure it remains a single line).

Next, force protocol version 1 by adding:

    Protocol 1

to BackupPC's ~/.ssh/config on the server.

Next, run "chmod -R go-rwx ~/.ssh" on the server and "chmod -R go-rwx /.ssh"
on the client.

Finally, test using:

    ssh -l root clientHostName whoami

=back

Finally, if this machine uses DHCP you will need to run nmbd (the
NetBios name server) from the Samba distribution so that the machine
responds to a NetBios name request. See the manual page and Samba
documentation for more information.

=back

=head2 Step 6: Running BackupPC

The installation contains an init.d backuppc script that can be copied
to /etc/init.d so that BackupPC can auto-start on boot.
See init.d/README for further instructions.

BackupPC should be ready to start.  If you installed the init.d script,
then you should be able to run BackupPC with:

    /etc/init.d/backuppc start

(This script can also be invoked with "stop" to stop BackupPC and "reload"
to tell BackupPC to reload config.pl and the hosts file.)

Otherwise, just run

     __INSTALLDIR__/bin/BackupPC -d

as user __BACKUPPCUSER__.  The -d option tells BackupPC to run as a daemon
(ie: it does an additional fork).

Any immediate errors will be printed to stderr and BackupPC will quit.
Otherwise, look in __TOPDIR__/log/LOG and verify that BackupPC reports
it has started and all is ok.

=head2 Step 7: Talking to BackupPC

Note: as of version 1.5.0, BackupPC no longer supports telnet
to its TCP port.  First off, a unix domain socket is used
instead of a TCP port.  (The TCP port can still be re-enabled
if your installation has apache and BackupPC running on different
machines.)  Secondly, even if you still use the TCP port, the
messages exchanged over this interface are now protected by
an MD5 digest based on a shared secret (see $Conf{ServerMesgSecret})
as well as sequence numbers and per-session unique keys, preventing
forgery and replay attacks.

You should verify that BackupPC is running by using BackupPC_serverMesg.
This sends a message to BackupPC via the unix (or TCP) socket and prints
the response.

You can request status information and start and stop backups using this
interface. This socket interface is mainly provided for the CGI interface
(and some of the BackupPC sub-programs use it too).  But right now we just
want to make sure BackupPC is happy.  Each of these commands should
produce some status output:

    __INSTALLDIR__/bin/BackupPC_serverMesg status info
    __INSTALLDIR__/bin/BackupPC_serverMesg status jobs
    __INSTALLDIR__/bin/BackupPC_serverMesg status hosts

The output should be some hashes printed with Data::Dumper.  If it
looks cryptic and confusing, and doesn't look like an error message,
then all is ok.

The jobs status should initially show just BackupPC_trashClean.
The hosts status should produce a list of every host you have listed
in __TOPDIR__/conf/hosts as part of a big cryptic output line.

You can also request that all hosts be queued:

    __INSTALLDIR__/bin/BackupPC_serverMesg backup all

At this point you should make sure the CGI interface works since
it will be much easier to see what is going on.  That's our
next subject.

=head2 Step 8: CGI interface

The CGI interface script, BackupPC_Admin, is a powerful and flexible
way to see and control what BackupPC is doing.  It is written for an
Apache server.  If you don't have Apache, see L<http://www.apache.org>.

There are two options for setting up the CGI interface: standard
mode and using mod_perl.  Mod_perl provides much higher performance
(around 15x) and is the best choice if your Apache was built with
mod_perl support.  To see if your apache was built with mod_perl
run this command:

    httpd -l | egrep mod_perl

If this prints mod_perl.c then your Apache supports mod_perl.

Using mod_perl with BackupPC_Admin requires a dedicated Apache
to be run as the BackupPC user (__BACKUPPCUSER__).  This is
because BackupPC_Admin needs permission to access various files
in BackupPC's data directories.  In contrast, the standard
installation (without mod_perl) solves this problem by having
BackupPC_Admin installed as setuid to the BackupPC user, so that
BackupPC_Admin runs as the BackuPC user.

Here are some specifics for each setup:

=over 4

=item Standard Setup

The CGI interface should have been installed by the configure.pl script
in __CGIDIR__/BackupPC_Admin.  BackupPC_Admin should have been installed
as setuid to the BackupPC user (__BACKUPPCUSER__), in addition to user
and group execute permission.

You should be very careful about permissions on BackupPC_Admin and
the directory __CGIDIR__: it is important that normal users cannot
directly execute or change BackupPC_Admin, otherwise they can access
backup files for any PC. You might need to change the group ownership
of BackupPC_Admin to a group that Apache belongs to so that Apache
can execute it (don't add "other" execute permission!).
The permissions should look like this:

    ls -l __CGIDIR__/BackupPC_Admin
    -swxr-x---    1 __BACKUPPCUSER__   web      82406 Jun 17 22:58 __CGIDIR__/BackupPC_Admin

The setuid script won't work unless perl on your machine was installed
with setuid emulation.  This is likely the problem if you get an error
saying such as "Wrong user: my userid is 25, instead of 150", meaning
the script is running as the httpd user, not the BackupPC user.
This is because setuid scripts are disabled by the kernel in most
flavors of unix and linux.

To see if your perl has setuid emulation, see if there is a program
called sperl5.6.0 or sperl5.6.1 in the place where perl is installed.
If you can't find this program, then you have two options: rebuild
and reinstall perl with the setuid emulation turned on (answer "y" to
the question "Do you want to do setuid/setgid emulation?" when you
run perl's configure script), or switch to the mod_perl alternative
for the CGI script (which doesn't need setuid to work).

=item Mod_perl Setup

The advantage of the mod_perl setup is that no setuid script is needed,
and there is a huge performance advantage.  Not only does all the perl
code need to be parsed just once, the config.pl and hosts files, plus
the connection to the BackupPC server are cached between requests.  The
typical speedup is around 15 times.

To use mod_perl you need to run Apache as user __BACKUPPCUSER__.
If you need to run multiple Apache's for different services then
you need to create multiple top-level Apache directories, each
with their own config file.  You can make copies of /etc/init.d/httpd
and use the -d option to httpd to point each http to a different
top-level directory.  Or you can use the -f option to explicitly
point to the config file.  Multiple Apache's will run on different
Ports (eg: 80 is standard, 8080 is a typical alternative port accessed
via http://yourhost.com:8080).

Inside BackupPC's Apache http.conf file you should check the
settings for ServerRoot, DocumentRoot, User, Group, and Port.  See 
L<http://httpd.apache.org/docs/server-wide.html> for more details.

For mod_perl, BackupPC_Admin should not have setuid permission, so
you should turn it off:

    chmod u-s __CGIDIR__/BackupPC_Admin

To tell Apache to use mod_perl to execute BackupPC_Admin, add this
to Apache's httpd.conf file:

    <IfModule mod_perl.c>
        PerlModule Apache::Registry
        PerlTaintCheck On
        <Location /cgi-bin/BackupPC/BackupPC_Admin>   # <--- change path as needed
           SetHandler perl-script
           PerlHandler Apache::Registry
           Options ExecCGI
        </Location>
    </IfModule>

There are other optimizations and options with mod_perl.  For
example, you can tell mod_perl to preload various perl modules,
which saves memory compared to loading separate copies in every
Apache process after they are forked. See Stas's definitive
mod_perl guide at L<http://perl.apache.org/guide>.

=back

BackupPC_Admin requires that users are authenticated by Apache.
Specifically, it expects that Apache sets the REMOTE_USER environment
variable when it runs.  There are several ways to do this.  One way
is to create a .htaccess file in the cgi-bin directory that looks like:

    AuthGroupFile /etc/httpd/conf/group    # <--- change path as needed
    AuthUserFile /etc/http/conf/passwd     # <--- change path as needed
    AuthType basic
    AuthName "access"
    require valid-user

You will also need "AllowOverride Indexes AuthConfig" in the Apache
httpd.conf file to enable the .htaccess file. Alternatively, everything
can go in the Apache httpd.conf file inside a Location directive. The
list of users and password file above can be extracted from the NIS
passwd file.

One alternative is to use LDAP.  In Apache's http.conf add these lines:

    LoadModule auth_ldap_module   modules/auth_ldap.so
    AddModule auth_ldap.c

    # cgi-bin - auth via LDAP (for BackupPC)
    <Location /cgi-binBackupPC/BackupPC_Admin>    # <--- change path as needed
      AuthType Basic
      AuthName "BackupPC login"
      # replace MYDOMAIN, PORT, ORG and CO as needed
      AuthLDAPURL ldap://ldap.MYDOMAIN.com:PORT/o=ORG,c=CO?uid?sub?(objectClass=*)
      require valid-user
    </Location>

If you want to defeat the user authentication you can force a
particular user name by getting Apache to set REMOTE_USER, eg,
to hardcode the user to www you could add this to httpd.conf:

    <Location /cgi-bin/BackupPC/BackupPC_Admin>   # <--- change path as needed
        Setenv REMOTE_USER www
    </Location>

Finally, you should also edit the config.pl file and adjust, as necessary,
the CGI-specific settings.  They're near the end of the config file. In
particular, you should specify which users or groups have administrator
(privileged) access.  Also, the configure.pl script placed various
images into $Conf{CgiImageDir} that BackupPC_Admin needs to serve
up.  You should make sure that $Conf{CgiImageDirURL} is the correct
URL for the image directory.

=head2 Other installation topics

=over 4

=item Copying the pool

If the pool disk requirements grow you might need to copy the entire
data directory to a new (bigger) file system.  Hopefully you are lucky
enough to avoid this by having the data directory on a RAID file system
or LVM that allows the capacity to be grown in place by adding disks.

The backup data directories contain large numbers of hardlinks.  If
you try to copy the pool the target directory will occupy a lot more
space if the hardlinks aren't re-established.

The GNU cp program with the -a option is aware of hardlinks and knows
to re-establish them.  So GNU cp -a is the recommended way to copy
the data directory and pool.  Don't forget to stop BackupPC while
the copy runs.

=item Compressing an existing pool

If you are upgrading BackupPC and want to turn compression on you have
two choices:

=over 4

=item *

Simply turn on compression.  All new backups will be compressed. Both old
(uncompressed) and new (compressed) backups can be browsed and viewed.
Eventually, the old backups will expire and all the pool data will be
compressed. However, until the old backups expire, this approach could
require 60% or more additional pool storage space to store both
uncompressed and compressed versions of the backup files.

=item *

Convert all the uncompressed pool files and backups to compressed.
The script __INSTALLDIR__/bin/BackupPC_compressPool does this.
BackupPC must not be running when you run BackupPC_compressPool.
Also, there must be no existing compressed backups when you
run BackupPC_compressPool.

BackupPC_compressPool compresses all the files in the uncompressed pool
(__TOPDIR__/pool) and moves them to the compressed pool
(__TOPDIR__/cpool). It rewrites the files in place, so that the
existing hardlinks are not disturbed.

=back

The rest of this section discusses how to run BackupPC_compressPool.

BackupPC_compressPool takes three command line options:

=over 4

=item -t

Test mode: do everything except actually replace the pool files.
Useful for estimating total run time without making any real
changes.

=item -r

Read check: re-read the compressed file and compare it against
the original uncompressed file.  Can only be used in test mode.

=item -c #

Number of children to fork. BackupPC_compressPool can take a long time
to run, so to speed things up it spawns four children, each working on a
different part of the pool. You can change the number of children with
the -c option.

=back

Here are the recommended steps for running BackupPC_compressPool:

=over 4

=item *

Stop BackupPC (eg: "/etc/init.d/backuppc stop").

=item *

Set $Conf{CompressLevel} to a non-zero number (eg: 3).

=item *

Do a dry run of BackupPC_compressPool.  Make sure you run this as
the BackupPC user (__BACKUPPCUSER__):

    BackupPC_compressPool -t -r

The -t option (test mode) makes BackupPC_compressPool do all the steps,
but not actually change anything. The -r option re-reads the compressed
file and compares it against the original.

BackupPC_compressPool gives a status as it completes each 1% of the job.
It also shows the cumulative compression ratio and estimated completion
time.  Once you are comfortable that things look ok, you can kill
BackupPC_compressPool or wait for it to finish.

=item *

Now you are ready to run BackupPC_compressPool for real.  Once again,
as the BackupPC user (__BACKUPPCUSER__), run:

    BackupPC_compressPool

You should put the output into a file and tail this file.  (The running
time could be twice as long as the test mode since the test mode file
writes are immediately followed by an unlink, so in test mode it is
likely the file writes never make it to disk.)

It is B<critical> that BackupPC_compressPool runs to completion before
re-starting BackupPC.  Before BackupPC_compressPool completes, none of
the existing backups will be in a consistent state.  If you must stop
BackupPC_compressPool for some reason, send it an INT or TERM signal
and give it several seconds (or more) to clean up gracefully.
After that, you can re-run BackupPC_compressPool and it will start
again where it left off.  Once again, it is critical that it runs
to 100% completion.

=back

After BackupPC_compressPool completes you should have a complete set
of compressed backups (and your disk usage should be lower).  You
can now re-start BackupPC.

=back

=head2 Debugging installation problems

This section will probably grow based on the types of questions on
the BackupPC mail list.

Assuming BackupPC can start correctly you should inspect __TOPDIR__/log/LOG
for any errors.  Assuming backups for a particular host start, you
should be able to look in __TOPDIR__/pc/$host/LOG for error messages
specific to that host.

The most likely problems will relate to connecting to the smb shares on
each host.  On each failed backup, a file __TOPDIR__/pc/$host/XferERR will
be created. This is the stderr output from smbclient. The first line
will show the full smbclient command that was run. Based on the error
messages you should figure out what is wrong.  Possible errors on the
server side are invalid host, invalid share name, bad username or password.
Possible errors on the client side are misconfiguration of the share,
username or password.

You should run smbclient manually and verify that you can connect to
the host in interactive mode, eg:

    smbclient '\\hostName\shareName' -U userName

shareName should match the $Conf{SmbShareName} setting and userName
should match the the $Conf{SmbShareUserName} setting.

You will be prompted for the password. You should then see this prompt:

    smb: \>

Verify that "ls" works and then type "quit" to exit.

Secondly, you should also verify that nmblookup correctly returns
the netbios name.  This is essential for DHCP hosts, and depending
upon the setting of $Conf{FixedIPNetBiosNameCheck} might also be
required for fixed IP address hosts too.  Run this command:

    nmblookup -A hostName

Verify that the host name is printed.  The output might look like:

    received 7 names
            DELLLS13        <00> -         P <ACTIVE> 
            DOMAINNAME      <00> - <GROUP> P <ACTIVE> 
            DELLLS13        <20> -         P <ACTIVE> 
            DOMAINNAME      <1e> - <GROUP> P <ACTIVE> 
            DELLLS13        <03> -         P <ACTIVE> 
            DELLLS13$       <03> -         P <ACTIVE> 
            CRAIG           <03> -         P <ACTIVE> 

The first name, converted to lower case, is used for the host name.

=head1 Restore functions

BackupPC supports several different methods for restoring files. The
most convenient restore options are provided via the CGI interface.
Alternatively, backup files can be restored using manual commands.

=head2 CGI restore options

By selecting a host in the CGI interface, a list of all the backups
for that machine will be displayed.  By selecting the backup number
you can navigate the shares and directory tree for that backup.

BackupPC's CGI interface automatically fills incremental backups
with the corresponding full backup, which means each backup has
a filled appearance.  Therefore, there is no need to do multiple
restores from the incremental and full backups: BackupPC does all
the hard work for you.  You simply select the files and directories
you want from the correct backup vintage in one step.

You can download a single backup file at any time simply by selecting
it.  Your browser should prompt you with the file name and ask you
whether to open the file or save it to disk.

Alternatively, you can select one or more files or directories in
the currently selected directory and select "Restore selected files".
(If you need to restore selected files and directories from several
different parent directories you will need to do that in multiple
steps.)

If you select all the files in a directory, BackupPC will replace
the list of files with the parent directory.  You will be presented
with a screen that has three options:

=over 4

=item Option 1: Direct Restore

With this option the selected files and directories are restored
directly back onto the host, by default in their original location.
Any old files with the same name will be overwritten, so use caution.
You can optionally change the target host name, target share name,
and target path prefix for the restore, allowing you to restore the
files to a different location.

Once you select "Start Restore" you will be prompted one last time
with a summary of the exact source and target files and directories
before you commit.  When you give the final go ahead the restore
operation will be queued like a normal backup job, meaning that it
will be deferred if there is a backup currently running for that host.
When the restore job is run, smbclient or tar is used (depending upon
$Conf{XferMethod}) to actually restore the files.  Sorry, there is
currently no option to cancel a restore that has been started.

A record of the restore request, including the result and list of
files and directories, is kept.  It can be browsed from the host's
home page.  $Conf{RestoreInfoKeepCnt} specifies how many old restore
status files to keep.

=item Option 2: Download Zip archive

With this option a zip file containing the selected files and directories
is downloaded.  The zip file can then be unpacked or individual files
extracted as necessary on the host machine. The compression level can be
specified.  A value of 0 turns off compression.

When you select "Download Zip File" you should be prompted where to
save the restore.zip file.

BackupPC does not consider downloading a zip file as an actual
restore operation, so the details are not saved for later browsing
as in the first case.  However, a mention that a zip file was
downloaded by a particular user, and a list of the files, does
appear in BackupPC's log file.

=item Option 3: Download Tar archive

This is identical to the previous option, except a tar file is downloaded
rather than a zip file (and there is currently no compression option).

=back

=head2 Command-line restore options

Apart from the CGI interface, BackupPC allows you to restore files
and directories from the command line.  The following programs can
be used:

=over 4

=item BackupPC_zcat

For each file name argument it inflates (uncompresses) the file and
writes it to stdout.  To use BackupPC_zcat you could give it the
full file name, eg:

    __INSTALLDIR__/bin/BackupPC_zcat __TOPDIR__/pc/host/5/fc/fcraig/fexample.txt > example.txt

It's your responsibility to make sure the file is really compressed:
BackupPC_zcat doesn't check which backup the requested file is from.

=item BackupPC_tarCreate

BackupPC_tarCreate creates a tar file for any files or directories in
a particular backup.  Merging of incrementals is done automatically,
so you don't need to worry about whether certain files appear in the
incremental or full backup.

The usage is:

   BackupPC_tarCreate [-t] [-h host] [-n dumpNum] [-s shareName]
                    [-r pathRemove] [-p pathAdd]
                    files/directories...

The command-line files and directories are relative to the specified
shareName.  The tar file is written to stdout.

The required options are:

=over 4

=item -h host

host from which the tar archive is created

=item -n dumpNum

dump number from which the tar archive is created

=item -s shareName

share name from which the tar archive is created

=back

Other options are:

=over 4

=item -t

print summary totals

=item -r pathRemove

path prefix that will be replaced with pathAdd

=item -p pathAdd

new path prefix

=back

The -h, -n and -s options specify which dump is used to generate
the tar archive.  The -r and -p options can be used to relocate
the paths in the tar archive so extracted files can be placed
in a location different from their original location.

=item BackupPC_zipCreate

BackupPC_zipCreate creates a zip file for any files or directories in
a particular backup.  Merging of incrementals is done automatically,
so you don't need to worry about whether certain files appear in the
incremental or full backup.

The usage is:

   BackupPC_zipCreate [-t] [-h host] [-n dumpNum] [-s shareName]
                    [-r pathRemove] [-p pathAdd] [-c compressionLevel]
                   files/directories...

The command-line files and directories are relative to the specified
shareName.  The zip file is written to stdout.

The required options are:

=over 4

=item -h host

host from which the zip archive is created

=item -n dumpNum

dump number from which the zip archive is created

=item -s shareName

share name from which the zip archive is created

=back

Other options are:

=over 4

=item -t

print summary totals

=item -r pathRemove

path prefix that will be replaced with pathAdd

=item -p pathAdd

new path prefix

=item -c level

compression level (default is 0, no compression)

=back

The -h, -n and -s options specify which dump is used to generate
the zip archive.  The -r and -p options can be used to relocate
the paths in the zip archive so extracted files can be placed
in a location different from their original location.

=back

Each of these programs reside in __INSTALLDIR__/bin.

=head1 BackupPC Design

=head2 Some design issues

=over 4

=item Pooling common files

To quickly see if a file is already in the pool, an MD5 digest of the
file length and contents is used as the file name in the pool. This
can't guarantee a file is identical: it just reduces the search to
often a single file or handful of files. A complete file comparison
is always done to verify if two files are really the same.

Identical files on multiples backups are represented by hard links.
Hardlinks are used so that identical files all refer to the same
physical file on the server's disk. Also, hard links maintain
reference counts so that BackupPC knows when to deleted unused files
from the pool.

For the computer-science majors among you, you can think of the pooling
system used by BackupPC as just a chained hash table stored on a (big)
file system.

=item The hashing function

There is a tradeoff between how much of file is used for the MD5 digest
and the time taken comparing all the files that have the same hash.

Using the file length and just the first 4096 bytes of the file for the
MD5 digest produces some repetitions.  One example: with 900,000 unique
files in the pool, this hash gives about 7,000 repeated files, and in
the worst case 500 files have the same hash.  That's not bad: we only
have to do a single file compare 99.2% of the time.  But in the worst
case we have to compare as many as 500 files checking for a match.

With a modest increase in CPU time, if we use the file length and the
first 256K of the file we now only have 500 repeated files and in the
worst case around 20 files have the same hash. Furthermore, if we
instead use the first and last 128K of the file (more specifically, the
first and eighth 128K chunks for files larger than 1MB) we get only 300
repeated files and in the worst case around 20 files have the same hash.

Based on this experimentation, this is the hash function used by BackupPC.
It is important that you don't change the hash function after files
are already in the pool.  Otherwise your pool will grow to twice the
size until all the old backups (and all the old files with old hashes)
eventually expire.

=item Compression

BackupPC supports compression. It uses the deflate and inflate methods
in the Compress::Zlib module, which is based on the zlib compression
library (see L<http://www.gzip.org/zlib/>).

The $Conf{CompressLevel} setting specifies the compression level to use.
Zero (0) means no compression. Compression levels can be from 1 (least
cpu time, slightly worse compression) to 9 (most cpu time, slightly
better compression). The recommended value is 3. Changing it to 5, for
example, will take maybe 20% more cpu time and will get another 2-3%
additional compression. Diminishing returns set in above 5.  See the zlib
documentation for more information about compression levels.

BackupPC implements compression with minimal CPU load. Rather than
compressing every incoming backup file and then trying to match it
against the pool, BackupPC computes the MD5 digest based on the
uncompressed file, and matches against the candidate pool files by
comparing each uncompressed pool file against the incoming backup file.
Since inflating a file takes roughly a factor of 10 less CPU time than
deflating there is a big saving in CPU time.

The combination of pooling common files and compression can yield
a factor of 8 or more overall saving in backup storage.

=back

=head2 BackupPC operation

BackupPC reads the configuration information from
__TOPDIR__/conf/config.pl. It then runs and manages all the backup
activity. It maintains queues of pending backup requests, user backup
requests and administrative commands. Based on the configuration various
requests will be executed simultaneously.

As specified by $Conf{WakeupSchedule}, BackupPC wakes up periodically
to queue backups on all the PCs.  This is a four step process:

=over 4

=item 1

For each host and DHCP address backup requests are queued on the
background command queue.

=item 2

For each PC, BackupPC_dump is forked. Several of these may be run in
parallel, based on the configuration. First a ping is done to see if the
machine is alive. If this is a DHCP address, nmblookup is run to get
the netbios name, which is used as the host name. The file
__TOPDIR__/pc/$host/backups is read to decide whether a full or
incremental backup needs to be run. If no backup is scheduled, or the ping
to $host fails, then BackupPC_dump exits.

The backup is done using samba's smbclient or tar over ssh/rsh/nfs piped
into BackupPC_tarExtract, extracting the backup into __TOPDIR__/pc/$host/new.
The smbclient or tar output is put into __TOPDIR__/pc/$host/XferLOG.

As BackupPC_tarExtract extracts the files from smbclient, it checks each
file in the backup to see if it is identical to an existing file from
any previous backup of any PC. It does this without needed to write the
file to disk. If the file matches an existing file, a hardlink is
created to the existing file in the pool. If the file does not match any
existing files, the file is written to disk and the file name is saved
in __TOPDIR__/pc/$host/NewFileList for later processing by
BackupPC_link.  BackupPC_tarExtract can handle arbitrarily large
files and multiple candidate matching files without needing to
write the file to disk in the case of a match.  This significantly
reduces disk writes (and also reads, since the pool file comparison
is done disk to memory, rather than disk to disk).

Based on the configuration settings, BackupPC_dump checks each
old backup to see if any should be removed.  Any expired backups
are moved to __TOPDIR__/trash for later removal by BackupPC_trashClean.

=item 3

For each complete, good, backup, BackupPC_link is run.
To avoid race conditions as new files are linked into the
pool area, only a single BackupPC_link program runs
at a time and the rest are queued.

BackupPC_link reads the NewFileList written by BackupPC_dump and
inspects each new file in the backup. It re-checks if there is a
matching file in the pool (another BackupPC_link
could have added the file since BackupPC_dump checked). If so, the file
is removed and replaced by a hard link to the existing file. If the file
is new, a hard link to the file is made in the pool area, so that this
file is available for checking against each new file and new backup.

Then, assuming $Conf{IncrFill} is set, for each incremental backup,
hard links are made in the new backup to all files that were not extracted
during the incremental backups.  The means the incremental backup looks
like a complete image of the PC (with the exception that files
that were removed on the PC since the last full backup will still
appear in the backup directory tree).

As of v1.03, the CGI interface knows how to merge unfilled
incremental backups will the most recent prior filled (full)
backup, giving the incremental backups a filled appearance.  The
default for $Conf{IncrFill} is off, since there is now no need to
fill incremental backups.  This saves some level of disk activity,
since lots of extra hardlinks are no longer needed (and don't have
to be deleted when the backup expires).

=item 4

BackupPC_trashClean is always run in the background to remove any
expired backups. Every 5 minutes it wakes up and removes all the files
in __TOPDIR__/trash.

Also, once each night, BackupPC_nightly is run to complete some additional
administrative tasks, such as cleaning the pool.  This involves removing
any files in the pool that only have a single hard link (meaning no backups
are using that file).  Again, to avoid race conditions, BackupPC_nightly
is only run when there are no BackupPC_dump or BackupPC_link processes
running.

=back

BackupPC also listens for TCP connections on $Conf{ServerPort}, which
is used by the CGI script BackupPC_Admin for status reporting and
user-initiated backup or backup cancel requests.

=head2 Storage layout

BackupPC resides in three directories:

=over 4

=item __INSTALLDIR__

Perl scripts comprising BackupPC reside in __INSTALLDIR__/bin,
libraries are in __INSTALLDIR__/lib and documentation
is in __INSTALLDIR__/doc.

=item __CGIDIR__

The CGI script BackupPC_Admin resides in this cgi binary directory.

=item __TOPDIR__

All of BackupPC's data (PC backup images, logs, configuration information)
is stored below this directory.

=back

Below __TOPDIR__ are several directories:

=over 4

=item __TOPDIR__/conf

The directory __TOPDIR__/conf contains:

=over 4

=item config.pl

Configuration file. See L<Configuration file|configuration file>
below for more details.

=item hosts

Hosts file, which lists all the PCs to backup.

=back

=item __TOPDIR__/log

The directory __TOPDIR__/log contains:

=over 4

=item LOG

Current (today's) log file output from BackupPC.

=item LOG.0 or LOG.0.z

Yesterday's log file output.  Log files are aged daily and compressed
(if compression is enabled), and old LOG files are deleted.

=item BackupPC.pid

Contains BackupPC's process id.

=item status.pl

A summary of BackupPC's status written periodically by BackupPC so
that certain state information can be maintained if BackupPC is
restarted.  Should not be edited.

=item UserEmailInfo.pl

A summary of what email was last sent to each user, and when the
last email was sent.  Should not be edited.

=back

=item __TOPDIR__/trash

Any directories and files below this directory are periodically deleted
whenever BackupPC_trashClean checks. When a backup is aborted or when an
old backup expires, BackupPC_dump simply moves the directory to
__TOPDIR__/trash for later removal by BackupPC_trashClean.

=item __TOPDIR__/pool

All uncompressed files from PC backups are stored below __TOPDIR__/pool.
Each file's name is based on the MD5 hex digest of the file contents.
Specifically, for files less than 256K, the file length and the entire
file is used. For files up to 1MB, the file length and the first and
last 128K are used. Finally, for files longer than 1MB, the file length,
and the first and eighth 128K chunks for the file are used.

Each file is stored in a subdirectory X/Y/Z, where X, Y, Z are the
first 3 hex digits of the MD5 digest.

For example, if a file has an MD5 digest of 123456789abcdef0,
the file is stored in __TOPDIR__/pool/1/2/3/123456789abcdef0.

The MD5 digest might not be unique (especially since not all the file's
contents are used for files bigger than 256K). Different files that have
the same MD5 digest are stored with a trailing suffix "_n" where n is
an incrementing number starting at 0. So, for example, if two additional
files were identical to the first, except the last byte was different,
and assuming the file was larger than 1MB (so the MD5 digests are the
same but the files are actually different), the three files would be
stored as:

        __TOPDIR__/pool/1/2/3/123456789abcdef0
        __TOPDIR__/pool/1/2/3/123456789abcdef0_0
        __TOPDIR__/pool/1/2/3/123456789abcdef0_1

Both BackupPC_dump (actually, BackupPC_tarExtract) and BackupPC_link are
responsible for checking newly backed up files against the pool. For
each file, the MD5 digest is used to generate a file name in the pool
directory. If the file exists in the pool, the contents are compared.
If there is no match, additional files ending in "_n" are checked.
(Actually, BackupPC_tarExtract compares multiple candidate files in
parallel.)  If the file contents exactly match, the file is created by
simply making a hard link to the pool file (this is done by
BackupPC_tarExtract as the backup proceeds). Otherwise,
BackupPC_tarExtract writes the new file to disk and a new hard link is
made in the pool to the file (this is done later by BackupPC_link).

Therefore, every file in the pool will have at least 2 hard links
(one for the pool file and one for the backup file below __TOPDIR__/pc).
Identical files from different backups or PCs will all be linked to
the same file.  When old backups are deleted, some files in the pool
might only have one link.  BackupPC_nightly checks the entire pool
and removes all files that have only a single link, thereby recovering
the storage for that file.

One other issue: zero length files are not pooled, since there are a lot
of these files and on most file systems it doesn't save any disk space
to turn these files into hard links.

=item __TOPDIR__/cpool

All compressed files from PC backups are stored below __TOPDIR__/cpool.
Its layout is the same as __TOPDIR__/pool, and the hashing function
is the same (and, importantly, based on the uncompressed file, not
the compressed file).

=item __TOPDIR__/pc/$host

For each PC $host, all the backups for that PC are stored below
the directory __TOPDIR__/pc/$host.  This directory contains the
following files:

=over 4

=item LOG

Current log file for this PC from BackupPC_dump.

=item LOG.0 or LOG.0.z

Last month's log file.  Log files are aged monthly and compressed
(if compression is enabled), and old LOG files are deleted.

=item XferERR or XferERR.z

Output from the transport program (ie: smbclient or tar)
for the most recent failed backup.

=item new

Subdirectory in which the current backup is stored.  This
directory is renamed if the backup succeeds.

=item XferLOG or XferLOG.z

Output from the transport program (ie: smbclient or tar)
for the current backup.

=item nnn (an integer)

Successful backups are in directories numbered sequentially starting at 0.

=item XferLOG.nnn or XferLOG.nnn.z

Output from the transport program (ie: smbclient or tar)
corresponding to backup number nnn.

=item RestoreInfo.nnn

Information about restore request #nnn including who, what, when, and
why. This file is in Data::Dumper format.  (Note that the restore
numbers are not related to the backup number.)

=item RestoreLOG.nnn.z

Output from smbclient or tar during restore #nnn.  (Note that the restore
numbers are not related to the backup number.)

=item config.pl

Optional configuration settings specific to this host.  Settings in this
file override the main configuration file.

=item backups

A tab-delimited ascii table listing information about each successful
backup, one per row.  The columns are:

=over 4

=item num

The backup number, an integer that starts at 0 and increments
for each successive backup.  The corresponding backup is stored
in the directory num (eg: if this field is 5, then the backup is
stored in __TOPDIR__/pc/$host/5).

=item type

Set to "full" or "incr" for full or incremental backup.

=item startTime

Start time of the backup in unix seconds.

=item endTime

Stop time of the backup in unix seconds.

=item nFiles

Number of files backed up (as reported by smbclient or tar).

=item size

Total file size backed up (as reported by smbclient or tar).

=item nFilesExist

Number of files that were already in the pool
(as determined by BackupPC_dump and BackupPC_link).

=item sizeExist

Total size of files that were already in the pool
(as determined by BackupPC_dump and BackupPC_link).

=item nFilesNew

Number of files that were not in the pool
(as determined by BackupPC_link).

=item sizeNew

Total size of files that were not in the pool
(as determined by BackupPC_link).

=item xferErrs

Number of errors or warnings from smbclient (zero for tar).

=item xferBadFile

Number of errors from smbclient that were bad file errors (zero for tar).

=item xferBadShare

Number of errors from smbclient that were bad share errors (zero for tar).

=item tarErrs

Number of errors from BackupPC_tarExtract.

=item compress

The compression level used on this backup.  Zero or empty means no
compression.

=item sizeExistComp

Total compressed size of files that were already in the pool
(as determined by BackupPC_dump and BackupPC_link).

=item sizeNewComp

Total compressed size of files that were not in the pool
(as determined by BackupPC_link).

=item noFill

Set if this backup has not been filled in with the most recent
previous filled or full backup.  See $Conf{IncrFill}.

=item fillFromNum

If this backup was filled (ie: noFill is 0) then this is the
number of the backup that it was filled from

=item mangle

Set if this backup has mangled file names and attributes.  Always
true for backups in v1.4.0 and above.  False for all backups prior
to v1.4.0.

=back

=item restores

A tab-delimited ascii table listing information about each requested
restore, one per row.  The columns are:

=over 4

=item num

Restore number (matches the suffix of the RestoreInfo.nnn and
RestoreLOG.nnn.z file), unrelated to the backup number.

=item startTime

Start time of the restore in unix seconds.

=item endTime

End time of the restore in unix seconds.

=item result

Result (ok or failed).

=item errorMsg

Error message if restore failed.

=item nFiles

Number of files restored.

=item size

Size in bytes of the restored files.

=item tarCreateErrs

Number of errors from BackupPC_tarCreate during restore.

=item xferErrs

Number of errors from smbclient or tar during restore.

=back

=back

=back

=head2 Compressed file format

The compressed file format is as generated by Compress::Zlib::deflate
with one minor, but important, tweak. Since Compress::Zlib::inflate
fully inflates its argument in memory, it could take large amounts of
memory if it was inflating a highly compressed file. For example, a
200MB file of 0x0 bytes compresses to around 200K bytes. If
Compress::Zlib::inflate was called with this single 200K buffer, it
would need to allocate 200MB of memory to return the result.

BackupPC watches how efficiently a file is compressing. If a big file
has very high compression (meaning it will use too much memory when it
is inflated), BackupPC calls the flush() method, which gracefully
completes the current compression.  BackupPC then starts another
deflate and simply appends the output file.  So the BackupPC compressed
file format is one or more concatenated deflations/flushes.  The specific
ratios that BackupPC uses is that if a 6MB chunk compresses to less
than 64K then a flush will be done.

Back to the example of the 200MB file of 0x0 bytes.  Adding flushes
every 6MB adds only 200 or so bytes to the 200K output.  So the
storage cost of flushing is negligible.

To easily decompress a BackupPC compressed file, the script
BackupPC_zcat can be found in __INSTALLDIR__/bin.  For each
file name argument it inflates the file and writes it to stdout.

=head2 File name mangling

Backup file names are stored in "mangled" form. Each node of
a path is preceded by "f" (mnemonic: file), and special characters
(\n, \r, % and /) are URI-encoded as "%xx", where xx is the ascii
character's hex value.  So c:/craig/example.txt is now stored as
fc/fcraig/fexample.txt.

This was done mainly so meta-data could be stored alongside the backup
files without name collisions. In particular, the attributes for the
files in a directory are stored in a file called "attrib", and mangling
avoids file name collisions (I discarded the idea of having a duplicate
directory tree for every backup just to store the attributes). Other
meta-data (eg: rsync checksums) could be stored in file names preceded
by, eg, "c". There are two other benefits to mangling: the share name
might contain "/" (eg: "/home/craig" for tar transport), and I wanted
that represented as a single level in the storage tree. Secondly, as
files are written to NewFileList for later processing by BackupPC_link,
embedded newlines in the file's path will cause problems which are
avoided by mangling.

The CGI script undoes the mangling, so it is invisible to the user.
Old (unmangled) backups are still supported by the CGI
interface.

=head2 Special files

Linux/unix file systems support several special file types: symbolic
links, character and block device files, fifos (pipes) and unix-domain
sockets. All except unix-domain sockets are supported by BackupPC
(there's no point in backing up or restoring unix-domain sockets since
they only have meaning after a process creates them). Symbolic links are
stored as a plain file whose contents are the contents of the link (not
the file it points to). This file is compressed and pooled like any
normal file. Character and block device files are also stored as plain
files, whose contents are two integers separated by a comma; the numbers
are the major and minor device number. These files are compressed and
pooled like any normal file. Fifo files are stored as empty plain files
(which are not pooled since they have zero size). In all cases, the
original file type is stored in the attrib file so it can be correctly
restored.

Hardlinks are also supported.  When GNU tar first encounters a file with
more than one link (ie: hardlinks) it dumps it as a regular file.  When
it sees the second and subsequent hardlinks to the same file, it dumps
just the hardlink information.  BackupPC correctly recognizes these
hardlinks and stores them just like symlinks: a regular text file
whose contents is the path of the file linked to.  The CGI script
will download the original file when you click on a hardlink.

Also, BackupPC_tarCreate has enough magic to re-create the hardlinks
dynamically based on whether or not the original file and hardlinks
are both included in the tar file.  For example, imagine a/b/x is a
hardlink to a/c/y.  If you use BackupPC_tarCreate to restore directory
a, then the tar file will include a/b/x as the original file and a/c/y
will be a hardlink to a/b/x.  If, instead you restore a/c, then the
tar file will include a/c/y as the original file, not a hardlink.

=head2 Attribute file format

The unix attributes for the contents of a directory (all the files and
directories in that directory) are stored in a file called attrib.
There is a single attrib file for each directory in a backup.
For example, if c:/craig contains a single file c:/craig/example.txt,
that file would be stored as fc/fcraig/fexample.txt and there would be an
attribute file in fc/fcraig/attrib (and also fc/attrib and ./attrib).
The file fc/fcraig/attrib would contain a single entry containing the
attributes for fc/fcraig/fexample.txt.

The attrib file starts with a magic number, followed by the
concatenation of the following information for each file:

=over 4

=item *

File name length in perl's pack "w" format (variable length base 128).

=item *

File name.

=item *

The unix file type, mode, uid, gid and file size divided by 4GB and
file size modulo 4GB (type mode uid gid sizeDiv4GB sizeMod4GB),
in perl's pack "w" format (variable length base 128).

=item *

The unix mtime (unix seconds) in perl's pack "N" format (32 bit integer).

=back

The attrib file is also compressed if compression is enabled.
See the lib/BackupPC/Attrib.pm module for full details.

Attribute files are pooled just like normal backup files.  This saves
space if all the files in a directory have the same attributes across
multiple backups, which is common.

=head2 Limitations

BackupPC isn't perfect (but it is getting better).  Here are some
limitations of BackupPC:

=over 4

=item Non-unix file attributes not backed up

smbclient doesn't extract the WinXX ACLs, so file attributes other than
the equivalent (as provided by smbclient) unix attributes are not
backed up.

=item Locked files are not backed up

Under WinXX a locked file cannot be read by smbclient.  Such files will
not be backed up.  This includes the WinXX system registry files.

This is especially troublesome for Outlook, which stores all its data
in a single large file and keeps it locked whenever it is running.
Since many users keep Outlook running all the time their machine
is up their Outlook file will not be backed up.  Sadly, this file
is the most important file to backup.  As one workaround, Microsoft has
a user-level application that periodically asks the user if they want to
make a copy of their outlook.pst file.  This copy can then be backed up
by BackupPC.  See L<http://office.microsoft.com/downloads/2002/pfbackup.aspx>.

Similarly, all of the data for WinXX services like SQL databases,
Exchange etc won't be backed up.  If these applications support
some kind of export or utility to save their data to disk then this
can =used to create files that BackupPC can backup.

So far, the best that BackupPC can do is send warning emails to
the user saying that their outlook files haven't been backed up in
X days.  (X is configurable.)  The message invites the user to
exit Outlook and gives a URL to manually start a backup.

I suspect there is a way of mirroring the outlook.pst file so
that at least the mirror copy can be backed up.  Or perhaps a
manual copy can be started at login.   Does some WinXX expert
know how to do this?

Comment: two users have noted that there are commercial OFM (open file
manager) products that are designed to solve this problem, for example
from St. Bernard or Columbia Data Products. Apparently Veritas and
Legato bundle this product with their commercial products.  See for
example L<http://www.stbernard.com/products/docs/ofm_whitepaperV8.pdf>.
If anyone tries these programs with BackupPC please tell us whether or
not they work.

=item Don't expect to reconstruct a complete WinXX drive

The conclusion from the last few items is that BackupPC is not intended
to allow a complete WinXX disk to be re-imaged from the backup. Our
approach to system restore in the event of catastrophic failure is to
re-image a new disk from a generic master, and then use the BackupPC
archive to restore user files.

It is likely that linux/unix backups done using tar (rather than
smb) can be used to reconstruct a complete file system, although
I haven't tried it.

=item Maximum Backup File Sizes

BackupPC can backup and manage very large file sizes, probably as large
as 2^51 bytes (when a double-precision number's mantissa can no longer
represent an integer exactly).  In practice, several things outside
BackupPC limit the maximum individual file size.  Any one of the
following items will limit the maximum individual file size:

=over 4

=item Perl

Perl needs to be compiled with uselargefiles defined. Check your
installation with:

    perl -V | egrep largefiles

Without this, the maximum file size will be 2GB.

=item File system

The BackupPC pool and data directories must be on a file system that
supports large files.

Without this, the maximum file size will be 2GB.

=item Transport

The transport mechanism also limits the maximum individual file size.

GNU tar maximum file size is limited by the tar header format. The tar
header uses 11 octal digits to represent the file size, which is 33 bits
or 8GB.  I vaguely recall (but I haven't recently checked) that GNU tar
uses an extra octal digit (replacing a trailing delimiter) if necessary,
allowing 64GB files.  So tar transport limits the maximum file size to
8GB or perhaps 64GB.  It is possible that files >= 8GB don't work; this
needs to be looked into.

Smbclient is limited to 4GB file sizes.  Moreover, a bug in smbclient
(mixing signed and unsigned 32 bit values) causes it to incorrectly
do the tar octal conversion for file sizes from 2GB-4GB.  BackupPC_tarExtract
knows about this bug and can recover the correct file size.  So smbclient
transport works up to 4GB file sizes.

=back

=item Some tape backup systems aren't smart about hard links

If you backup the BackupPC pool to tape you need to make sure that the
tape backup system is smart about hard links. For example, if you
simply try to tar the BackupPC pool to tape you will backup a lot more
data than is necessary.

Using the example at the start of the installation section, 65 hosts are
backed up with each full backup averaging 3.2GB. Storing one full backup
and two incremental backups per laptop is around 240GB of raw data. But
because of the pooling of identical files, only 87GB is used (with
compression the total is lower). If you run du or tar on the data
directory, there will appear to be 240GB of data, plus the size of the
pool (around 87GB), or 327GB total.

If your tape backup system is not smart about hard links an alternative
is to periodically backup just the last successful backup for each host
to tape.  Another alternative is to do a low-level dump of the pool
file system (ie: /dev/hda1 or similar) using dump(1).

Supporting more efficient tape backup is an area for further
development.

=item Incremental backups might included deleted files

To make browsing and restoring backups easier, incremental backups
are "filled-in" from the last complete backup when the backup is
browsed or restored.

However, if a file was deleted by a user after the last full backup, that
file will still appear in the "filled-in" incremental backup. This is not
really a specific problem with BackupPC, rather it is a general issue
with the full/incremental backup paradigm.  This minor problem could be
solved by having smbclient list all files when it does the incremental
backup.  Volunteers anyone?

=back

Comments or suggestions on these issues are welcome.

=head2 Security issues

Please read this section and consider each of the issues carefully.

=over 4

=item Smb share password

An important security risk is the manner in which the smb share
passwords are stored. They are in plain text. As described in
L<Step 3: Setting up config.pl|step 3: setting up config.pl> there are four
ways to tell BackupPC the smb share password (manually setting an environment
variable, setting the environment variable in /etc/init.d/backuppc,
putting the password in __TOPDIR__/conf/config.pl, or putting the
password in __TOPDIR__/pc/$host/config.pl). In the latter 3 cases the
smb share password appears in plain text in a file.

If you use any of the latter three methods please make sure that the file's
permission is appropriately restricted.  If you also use RCS or CVS, double
check the file permissions of the config.pl,v file.

In future versions there will probably be support for encryption of the
smb share password, but a private key will still have to be stored in a
protected place.  Comments and suggestions are welcome.

=item BackupPC socket server

In v1.5.0 the primary method for communication between the CGI program
(BackupPC_Admin) and the server (BackupPC) is via a unix-domain socket.
Since this socket has restricted permissions, no local user should be
able to connect to this port.  No backup or restore data passes through
this interface, but an attacker can start or stop backups and get status
through this port.

If the Apache server and BackupPC_Admin run on a different host to
BackupPC then a TCP port must be enabled by setting $Conf{ServerPort}.
Anyone can connect to this port.  To avoid possible attacks via the TCP
socket interface, every client message is protected by an MD5 digest.
The MD5 digest includes four items:

=over 4

=item *

a seed that is sent to the client when the connection opens

=item *

a sequence number that increments for each message

=item *

a shared secret that is stored in $Conf{ServerMesgSecret}

=item *

the message itself.

=back

The message is sent in plain text preceded by the MD5 digest.  A
snooper can see the plain-text seed sent by BackupPC and plain-text
message from the client, but cannot construct a valid MD5 digest since
the secret in $Conf{ServerMesgSecret} is unknown.  A replay attack is
not possible since the seed changes on a per-connection and
per-message basis.

So if you do enable the TCP port, please set $Conf{ServerMesgSecret}
to some hard-to-guess string.  A denial-of-service attack is possible
with the TCP port enabled.  Someone could simply connect many times
to this port, until BackupPC had exhausted all its file descriptors,
and this would cause new backups and the CGI interface to fail.  The
most secure solution is to run BackupPC and Apache on the same machine
and disable the TCP port.

By the way, if you have upgraded from a version of BackupPC prior to
v1.5.0 you should set $Conf{ServerPort} to -1 to disable the TCP port.

=item Installation permissions

It is important to check that the BackupPC scripts in __INSTALLDIR__/bin
and __INSTALLDIR__/lib cannot be edited by normal users. Check the
directory permissions too.

=item Pool permissions

It is important to check that the data files in __TOPDIR__/pool,
__TOPDIR__/pc and __TOPDIR__/trash cannot be read by normal users.
Normal users should not be able to see anything below __TOPDIR__.

=item Host shares

Enabling shares on hosts carries security risks.  If you are on a private
network and you generally trust your users then there should not be a
problem. But if you have a laptop that is sometimes on public networks
(eg: broadband or even dialup) you should be concerned.  A conservative
approach is to use firewall software, and only enable the netbios and
smb ports (137 and 139) on connections from the host running BackupPC.

=item SSH key security

Using ssh for linux/unix clients is quite secure, but the security is
only as good as the protection of ssh's private keys. If an attacker can
devise a way to run a shell as the BackupPC user then they will have
access to BackupPC's private ssh keys. They can then, in turn, ssh to
any client machine as root (or whichever user you have configured
BackupPC to use). This represents a serious compromise of your entire
network.  So in vulnerable networks, think carefully about how to protect
the machine running BackupPC and how to prevent attackers from gaining
shell access (as the BackupPC user) to the machine.

=item CGI interface

The CGI interface, __CGIDIR__/BackupPC_Admin, needs access to the pool
files so it is installed setuid to __BACKUPPCUSER__. The permissions of
this file need to checked carefully. It should be owned by
__BACKUPPCUSER__ and have user and group (but not other) execute
permission. To allow apache/httpd to execute it, the group ownership
should be something that apache/httpd belongs to.

The Apache configuration should be setup for AuthConfig style,
using a .htaccess file so that the user's name is passed into
the script as $ENV{REMOTE_USER}.

If normal users could directly run BackupPC_Admin then there is a serious
security hole: since it is setuid to __BACKUPPCUSER__ any user can
browse and restore any backups. Be aware that anyone who is allowed to
edit or create cgi scripts on your server can execute BackupPC_Admin as
any user!  They simply write a cgi script that sets $ENV{REMOTE_USER} and
then execs BackupPC_Admin.  The exec succeeds since httpd runs the first
script as user httpd/apache, which in turn has group permission to
execute BackupPC_Admin.

While this setup should be safe, a more conservative approach is to
run a dedicated Apache as user __BACKUPPCUSER__ on a different port.
Then BackupPC_Admin no longer needs to be setuid, and the cgi
directories can be locked down from normal users.  Moreover, this
setup is exactly the one used to support mod_perl, so this provides
both the highest performance and the lowest security risk.

=back

Comments and suggestions are welcome.

=head1 Configuration File

The BackupPC configuration file resides in __TOPDIR__/conf/config.pl.
Optional per-PC configuration files reside in __TOPDIR__/pc/$host/config.pl.
This file can be used to override settings just for a particular PC.

=head2 Modifying the main configuration file

The configuration file is a perl script that is executed by BackupPC, so
you should be careful to preserve the file syntax (punctuation, quotes
etc) when you edit it. It is recommended that you use CVS, RCS or some
other method of source control for changing config.pl.

BackupPC reads or re-reads the main configuration file and
the hosts file in three cases:

=over 4

=item *

Upon startup.

=item *

When BackupPC is sent a HUP (-1) signal.  Assuming you installed the 
init.d script, you can also do this with "/etc/init.d/backuppc reload".

=item *

When the modification time of config.pl file changes.  BackupPC
checks the modification time once during each regular wakeup.

=back

Whenever you change the configuration file you can either do
a kill -HUP BackupPC_pid or simply wait until the next regular
wakeup period.

Each time the configuration file is re-read a message is reported in the
LOG file, so you can tail it (or view it via the CGI interface) to make
sure your kill -HUP worked. Errors in parsing the configuration file are
also reported in the LOG file.

The optional per-PC configuration file (__TOPDIR__/pc/$host/config.pl)
is read whenever it is needed by BackupPC_dump, BackupPC_link and others.

=head2 Configuration file includes

If you have a heterogeneous set of clients (eg: a variety of WinXX and
linux/unix machines) you will need to create host-specific config.pl files
for some or all of these machines to customize the default settings from
the master config.pl file (at a minimum to set $Conf{XferMethod}).

Since the config.pl file is just regular perl code, you can include
one config file from another.  For example, imagine you had three general
classes of machines: WinXX desktops, linux machines in the DMZ and
linux desktops.  You could create three config files in __TOPDIR__/conf:

    __TOPDIR__/conf/ConfigWinDesktop.pl
    __TOPDIR__/conf/ConfigLinuxDMZ.pl
    __TOPDIR__/conf/ConfigLinuxDesktop.pl

From each client's directory you can either add a symbolic link to
the appropriate config file:

    cd __TOPDIR__/pc/$host
    ln -s ../../conf/ConfigWinDesktop.pl config.pl

or, better yet, create a config.pl file in __TOPDIR__/pc/$host
that contains this line:

    do "../../conf/ConfigWinDesktop.pl";

This alternative allows you to set other configuration options
specific to each host (perhaps even overriding the settings in
the included file).

Note that you could also include snippets of configuration settings
from the main configuration file.  However, be aware that the
modification-time checking that BackupPC does only applies to the
main configuration file: if you change one of the included files,
BackupPC won't notice.  You will need to either touch the main
configuration file too, or send BackupPC a HUP (-1) signal.

=head1 Configuration Parameters

The configuration parameters are divided into five general groups.
The first group (general server configuration) provides general
configuration for BackupPC.  The next two groups describe what to
backup, when to do it, and how long to keep it.  The fourth group
are settings for email reminders, and the final group contains
settings for the CGI interface.

All configuration settings in the second through fifth groups can
be overridden by the per-PC config.pl file.

__CONFIGPOD__

=head1 Version Numbers

Starting with v1.4.0 BackupPC switched to a X.Y.Z version numbering
system, instead of X.0Y. The first digit is for major new releases, the
middle digit is for significant feature releases and improvements (most
of the releases have been in this category), and the last digit is for
bug fixes. You should think of the old 1.00, 1.01, 1.02 and 1.03 as
1.0.0, 1.1.0, 1.2.0 and 1.3.0.

=head1 Author

Craig Barratt  <cbarratt@users.sourceforge.net>

See L<http://backuppc.sourceforge.net>.

=head1 Copyright

Copyright (C) 2001-2002 Craig Barratt

=head1 Credits

Ryan Kucera contributed the directory navigation code and images
for v1.5.0.  He also contributed the first skeleton of BackupPC_restore.

Guillaume Filion wrote BackupPC_zipCreate and added the CGI support
for zip download, in addition to some CGI cleanup, for v1.5.0.

Several people have reported bugs or made useful suggestions; see the
ChangeLog.

Your name could appear here in the next version!

=head1 License

This program is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by the
Free Software Foundation; either version 2 of the License, or (at your
option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
General Public License for more details.

You should have received a copy of the GNU General Public License in the
LICENSE file along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.