cback - Local and remote backups to CD-R/CD-RW media under Linux

cback [switches] action(s)

The cback script is a front-end to a Python package that supports backups of files on local and remote hosts to CD-R or CD-RW media over a secure network connection. The script is focused around weekly backups to a single disc, with the expectation that the disc will be changed or overwritten at the beginning of each week. If your hardware is new enough, the script can write multisession discs, allowing you to add to a disc in a daily fashion. Directories are backed up using tar and may be compressed using several different methods.

There are two kinds of machines in a Cedar Backup pool. One machine (the master) has a CD-R or CD-RW drive on it and is where the backup is written to disc. The others (clients) collect data to be written to disc by the master. Collectively, the master and client machines in a pool are all referred to as peer machines. There are four actions that take place as part of the backup process: collect, stage, store and purge. Both the master and the clients execute the collect and purge actions, but only the master executes the stage and store actions. The configuration file /etc/cback.conf controls the actions taken during collect, stage, store and purge actions.

-h, --help

Display usage/help listing.

-V, --version

Display version information.

-b, --verbose

Print verbose output to the screen as well writing to the logfile. When this option is enabled, most information that would normally be written to the logfile will also be written to the screen.

-q, --quiet

Run quietly (display no output to the screen).

-c, --config

Specify the path to an alternate configuration file. The default configuration file is /etc/cback.conf.

-f, --full

Perform a full backup, regardless of configuration. For the collect action, this means that any existing information related to incremental backups will be ignored and rewritten; for the store action, this means that a new disc will be started.

-l, --logfile

Specify the path to an alternate logfile. The default logfile file is /var/log/cback.log.

-o, --owner

Specify the ownership of the logfile, in the form user:group. The default ownership is root:adm, to match the Debian standard for most logfiles. This value will only be used when creating a new logfile. If the logfile already exists when the cback script is executed, it will retain its existing ownership and mode. Only user and group names may be used, not numeric uid and gid values.

-m, --mode

Specify the permissions for the logfile, using the numeric mode as in chmod(1). The default mode is 640 (-rw-r-----). This value will only be used when creating a new logfile. If the logfile already exists when the cback script is executed, it will retain its existing ownership and mode.

-O, --output

Record some sub-command output to the logfile. When this option is enabled, all output from system commands will be logged. This might be useful for debugging or just for reference. Cedar Backup uses system commands mostly for dealing with the CD recorder and its media.

-d, --debug

Write debugging information to the logfile. This option produces a high volume of output, and would generally only be needed when debugging a problem. This option implies the --output option, as well.

-s, --stack

Dump a Python stack trace instead of swallowing exceptions. This forces Cedar Backup to dump the entire Python stack trace associated with an error, rather than just progating last message it received back up to the user interface. Under some circumstances, this is useful information to include along with a bug report.

all

Take all normal actions (collect, stage, store, purge), in that order.

collect

Take the collect action, creating tarfiles for each directory specified in the collect section of the configuration file.

stage

Take the stage action, copying tarfiles from each peer in the backup pool to the daily staging directory, based on the stage section of the configuration file.

store

Take the store action, writing the daily staging directory to disc based on the store section of the configuration file.

purge

Take the purge action, removing old and outdated files as specified in the purge section of the configuration file.

rebuild

Rebuild the "this week's" disc based on the current contents of the staging directory. This option has been made available as a means to recover a disc that has been "trashed" due to a hardware or media error.

validate

Ensure that configuration is valid, but take no other action. Validation checks that the configuration file can be found and can be parsed, and also checks for typical configuration problems, such as directories that are not writable or problems with the target SCSI device.

Cedar Backup returns 0 (zero) upon normal completion, and six other error codes related to particular errors.

1

The Python interpreter version is < 2.3.

2

Error processing command-line arguments.

3

Error configuring logging.

4

Error parsing indicated configuration file.

5

Backup was interrupted with a CTRL-C or similar.

6

Error executing specified backup actions.

The script is designed to run as root, since otherwise it's difficult to back up system directories or write the CD-R/CD-RW device. However, pains are taken to use a backup user's effective user id (specified in configuration) when appropriate.

To use the script, you must specify at least one action to take. More than one of the "collect", "stage", "store" or "purge" actions may be specified, in any arbitrary order. The "all", "rebuild" or "validate" actions may not be combined with other actions. If more than one action is specified, then actions will be taken in a sensible order (generally collect, followed by stage, followed by store, followed by purge).

If you have configured any Cedar Backup extensions, then the actions associated with those extensions may also be specified on the command line. If you specify any other actions along with an extended action, the actions will be executed in a sensible order per configuration. The "all" action never executes extended actions, however.

Note that there is no facility for restoring backups. It is assumed that the user can deal with copying tarfiles off disc and using them to restore missing files as needed.

Finally, you should be aware that backups to CD-R can probably be read by any user which has permissions to mount the CD-R drive. If you intend to leave the backup disc in the drive at all times, you may want to consider this when setting up device permissions on your machine.

/etc/cback.conf - Default configuration file

/var/log/cback.log - Default log file

There probably are bugs in this code. However, it is in active use for my own backups, and I fix problems as I notice them. If you find a bug, please report it. If possible, give me all of the error messages that the script printed into its log, and also any stack-traces (exceptions) that Python printed. It would be even better if you could tell me how to reproduce the problem (i.e. by sending me your configuration file).

Report bugs to <support@cedar-solutions.com>.

Written by Kenneth J. Pronovici <pronovic@ieee.org>.

Copyright (c) 2004-2005 Kenneth J. Pronovici.

This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.