NAME
backup2l - low-maintenance backup/restore tool
SYNOPSIS
backup2l [ -c conffile ] [ -t backup-ID ] command
DESCRIPTION
backup2l is a tool for generating, maintaining and restoring backups on
a mountable file system (e. g. hard disk). The main design goals are
low maintenance effort, efficiency, transparency and robustness. It
features differential backups at multiple hierarchical levels and
provides rollback functionality.
All control files are stored together with the archives on the backup
device, and their contents are mostly self-explaining. Hence, in the
case of an emergency, a user does not only have to rely on the restore
functionality of backup2l, but can - if necessary - browse the files
and extract archives manually.
An open driver architecture allows to use virtually any archiving
program as a backend. Built-in drivers support .tar.gz, .tar.bz2, or
.afioz files. Further drivers can be added by the user. When restoring
data, an appropriate driver is selected automatically for each archive
depending on the suffix of the archive file.
The method of hierarchical differential backups is a generalization to
the concept of the "daily", "weekly" and "monthly" backups. Each
backup has a level and a serial number. Maximum-level backups are
comparable with daily differential backups, level-0 backups are full
backups. For example, let MAX_LEVEL be 4 and MAX_PER_LEVEL be 5. After
5 level-4 backups (e. g. after 5 days), a new level-3 backup is made.
After 5 level-3 backups (and 5*5 at level-4), a new level-2 backup is
made, and so on. Each differential backup contains the changes towards
the previous backup of the same or a lower level.
This scheme allows to efficiently generate small incremental backups at
short intervals. At the same time, the total number of archives that
have to be stored (or processed in the case of a restore) only
increases logarithmically with the number of backups since the last
full backup. Time-consuming full backups are only sparsely needed. In
the example above, a new full backup is only necessary after 780
(=5^4+5^3+5*5+5) days, while only at most 20 (=4*5) archives have to be
processed.
For backup2l, each backup archive is identified by its backup ID (BID).
The number of digits determines the level. Level-0 (full) backups have
a 1-digit BID, level-n backups have a BID of n+1 digits. The last
digit is a serial number, the prefix identifies the lower-level backups
on which a given backup is based on. For example, the archive 235
contains the differences towards archive 234, and to restore the file
system state of the time it was generated, the full backup 2, the
level-1 backups 21, 22, 23 and the level-2 backups 231, ..., 235 have
to be processed. All serial numbers are between 1 and 9, a zero in the
BID indicates that no archive of the respective level is contained in
the chain. For example, the level-3 backup 1201 is immediately based on
the level-1 backup 12.
For deciding whether a file is new or modified, backup2l looks at its
name, modification time, size, ownership and permissions. Unlike other
backup tools, the i-node is not considered in order to avoid problems
with non-Unix file systems like FAT32.
OPTIONS
-c, --conf conffile
This argument specifies the configuration file (default:
etc/backup2l.conf).
-t, --time BID
If present, this option selects a certain backup for the
--locate and --restore commands. E. g., the latter will restore
files and directories exactly as they were on the system at the
time when the specified backup was made. If not present, the
latest available backup is selected.
COMMANDS
-h, --help
Display the usage info.
-e, --estimate [ level ]
Prints the number of files, estimated amount of data and other
information on the backup that would be generated next. No
backup archives are actually created or removed. If specified,
the parameter level overrides the MAX_LEVEL setting.
-b, --backup [ level ]
Creates a new backup and removes old archives based on the given
configuration file. If specified, the parameter level overrides
the MAX_LEVEL setting. This is useful e. g. shortly before or
after major changes are performed with the file system. In this
case, a lower level should be specified in order to avoid that a
large number of files are backed up multiple times again.
-s, --get-summary
Shows a table describing each backup (date, size, files, ...)
and the file system usage of the backup device.
-a, --get-available [ pattern list ]
Shows all files removed and added for all backups. A ’+’ in the
output indicates that the file is new and thus contained in the
archive file. A ’-’ indicates that the file has been removed (or
replaced). If one or several patterns are supplied, grep(1) is
used to filter the list. All status messages go to stderr, so
that the generated file list can easily be redirected.
Note: The search pattern is not just applied to the file names,
but to the whole entry in the .list.gz file. This allows you to
not only search for file names but also for other attributes
like ownership, modification time etc. . In order to apply a
search pattern to file names only, precede it by "<space>/.*".
-l, --locate [ pattern list ]
Shows most recent backup location for active files. If one or
several patterns are supplied, grep(1) is used to filter the
list in the same way as for --get-available (see above) . All
status messages go to stderr, so that the generated file list
can easily be redirected.
Active files are files that have been on the system at the time
of the selected backup, which is either the latest backup or the
one specified by --time (see above). Files that were removed at
that time but are still stored in some later archive will not be
shown.
Altogether, this command tells you, which files have to be
extracted from which archive in order to restore the state of
the system at the time of the selected backup.
-r, --restore [ pattern list ]
Performs the same steps like --locate and then restores the
respective files. All files are restored relative to the current
directory. They can be restored to their original location by
cd’ing into / before, but this is not recommended.
-p, --purge BID list
Removes the specified backup archive(s) and all depending
backups.
-m, --make-check [ BID list ]
Creates (a) check file(s) for the specified archive(s) using
md5sum(1). If no BID is specified, check files are created
wherever missing.
-v, --verify [ BID list ]
Verifies the specified backup archive(s). If no BID is
specified, all existing archives are checked. If a check file
exists, this allows a comprehensive test including e. g. media
failures. If the check file is missing, only the existence of
all files and the immediate base archive are verified.
-x, --extract capacity max-free BID-list
Split and collect files to be stored on removable media (e. g.
CDs). capacity is the medium capacity in MB. max-free is the
maximum amount of empty space on each medium (except for the
last one, of course). BID-list specifies the archives and may
contain wildcards, e. g.: 1 ’2*’. The operation generates
enumbered subdirectories representing the media contents. Some
more files are generated that may be useful, e. g. to print
labels.
While guaranteeing a minimum waste of max-free MB per medium,
the collection procedure preserves the ordering of files and
keeps all control files of an archive always together on the
same medium. Large archive files are split into multiple files
with serial numbers appended to their names.
The operation is interactive. Just run it and look what it is
about to do. If that is not what you want, you can stop it.
CONFIGURATION
In the configuration file (/etc/backup2l.conf by default), the
following variables have to be set, following the bash(1) syntax:
FOR_VERSION=version
Defines the backup2l version for which the configuration file is
written. This way, future versions can automatically print a
warning if the syntax has changed.
SRCLIST=( source list )
This is a blank-separated list of all top-level directories to
make backups of. Directory names with spaces have to be quoted,
e. g.: SRCLIST=("/my dir" /another/dir). The last elements of
the list may be options for find(1), for example -xdev in order
to skip subdirs on other file systems like /dev or /proc.
SKIPCOND=( find condition )
Files for which this condition is ’true’ are not considered for
backup. See find(1) for information on how to formulate
possible conditions. Special characters ("(", ")", "!", ...)
must be quoted by a leading backslash ("\(", "\)", " \!", ...).
An empty condition (i. e. if you do not want any files to be
skipped) must be specified as "( -false )".
[ BACKUP_DEV="mount_point" ]
If defined, backup2l mounts the backup device before any
operation. Afterwards, it is unmounted unless it was already
mounted before.
BACKUP_DIR="backup dir"
Destination directory for backup files. This must be different
from MOUNT_POINT, i. e. a subdirectory on the device.
VOLNAME="volname"
This is a common prefix for all backup and control files.
Multiple backup volumes are possible if for each volume a
separate configuration file is written.
MAX_LEVEL=max_level
Maximum backup level. Possible values are 1..9.
MAX_PER_LEVEL=max_per_level
Number of differential backups per level. Possible values are
1..9.
MAX_FULL=max_full
Number of full backups kept. Possible values are 1..8.
GENERATIONS=generations
Number of backup generations to keep for each non-zero level.
Old backups are automatically removed as long as at least
GENERATIONS * MAX_PER_LEVEL backups for the respective level
remain.
For example, with MAX_LEVEL=3, MAX_PER_LEVEL=5, GENERATIONS=2 it
is always possible to access the last 10 level-3 (e. g. daily)
backups, the last 10 level-2 backups (e. g. 5, 10, 15, ..., 50
days old), and so on.
PRE_BACKUP () { do something }
This function is called before writing the backup. It can be
used to dump some important system information, e. g. the HD’s
partition table, to a file which is then backed up.
POST_BACKUP () { do something }
This function is called after writing the backup. Together with
PRE_BACKUP it can be used to stop and restart e. g. database or
mail services which may frequently alter some files that have to
be backed up.
[ AUTORUN=1 ]
If set to 1, backup2l performs the --backup operation when
invoked without arguments. Otherwise, the usage information is
shown.
[ SIZE_UNITS= B | K | M | G ]
Sets the units for archive sizes in summary listings to bytes,
KB, MB, or GB. If unset, a user-readable format is chosen
automatically. If set, the units are the same for the whole
table, which may be even more user-friendly.
[ CREATE_DRIVER="archive driver" ]
Selects an archive driver for creating backups. An archive
driver is responsible for managing backup files. If unset, the
default driver "DRIVER_TAR_GZ" is used. The --help operation
lists all available drivers. More drivers can be defined in the
configuration file (see below).
[ USER_DRIVER_LIST="user-defined drivers" ]
Declares additional, user-defined archive drivers which are
implemented in the configuration file. The sample configuration
file contains a commented example. Read it in order to learn how
to implement your own driver.
FILES
/etc/backup2l.conf
Configuration file.
VOLNAME.BID.tar.gz, VOLNAME.BID.afioz, ...
Archive files.
VOLNAME.BID.list.gz
List of all active files when the backup was made. Each file is
preceded with its size, modification time, and other
information.
VOLNAME.BID.new.gz
List of all new ore modified files when the backup was made
(pathnames only). Unless an error occured, this list reflects
the contents of the archive.
VOLNAME.BID.obsolete.gz
List of all obsolete files when the backup was made (pathnames
only).
VOLNAME.BID.skipped.gz
Complete list of all files that were skipped according to
SKIPMASK.
VOLNAME.BID.error.gz
This file is generated by comparing the .new.gz file with the
actual archive contents using diff(1). If the error file is
non-empty, something may have gone wrong.
VOLNAME.BID.check
MD5 check sums of all files of the present archive and the
.list.gz file of the base archive. This file is optional and
may be used by the --verify operation.
INVOCATION BY CRON
backup2l is designed to be run autonomously as a cron job. If the
variable AUTORUN is set, it generates a backup if invoked without any
parameters, and you can simply create a symlink, e. g. by:
ln -s ‘which backup2l‘ /etc/cron.daily/zz-backup2l
The "zz-" prefix causes the backup job to be the last one executed, so
that other jobs are not delayed if the backup takes somewhat longer.
The status output is e-mailed to root by the cron daemon.
MANIPULATING FILES AND CONFIGURATIONS
backup2l has been designed to be robust with respect to errors and
configuration changes. If the backup process is interrupted, e. g.
because of a shutdown while it is running, no serious data corruption
can occur. Some temporary files may remain which are cleaned up during
the next run. If file is changed during the backup generation, it may
not be contained in the current backup. However, it is guaranteed that
it is considered modified during the next backup.
In order to save disk space, e. g. after some archives have been copied
to external media, archive files (.tar.gz or .afioz, for example) can
safely be removed from the backup directory. As long as all control
files are kept, backup2l retains full functionality as far as possible.
The --restore command prompts for eventually missing archive files for
the respective request (and only those). The --extract command
completely ignores all backups with missing archive files.
The configuration, especially the settings for MAX_LEVEL,
MAX_PER_LEVEL, MAX_FULL and the specification of source files, can be
arbitrarily changed without having to expect data corruption. backup2l
will gracefully adapt the new settings during the next run.
BUGS
After a restore operation, the modification time of directories is
equal to the restoration time while for files it is equal to the
original modification time.
AUTHOR
backup2l was written by Gundolf Kiefer <gundolfk at web.de>.
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.
SEE ALSO
tar(1), afio(1), find(1), grep(1), md5sum(1)