obnam.1.in

.\" Copyright 2010-2017  Lars Wirzenius
.\"
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.TH OBNAM 1
.SH NAME
obnam \- make, restore, and manipulate backups
.SH SYNOPSIS
.SH DESCRIPTION
.B obnam
makes, restores, manipulates, and otherwise deals with backups.
It can store backups on a local disk or to a server via sftp.
Every backup generation looks like a fresh snapshot,
but is really incremental:
the user does not need to worry whether it's a full backup or not.
Only changed data is backed up,
and if a chunk of data is already backed up in another file,
that data is re-used.
.PP
The place where backed up data is placed is called the
backup repository.
A repository may be, for example, a directory on an sftp server,
or a directory on a USB hard disk.
A single repository may contain backups from several clients.
Their data will intermingle as if they were using separate repositories,
but if one client backs up a file, the others may re-use the data.
.PP
.B obnam
command line syntax consists of a
.I command
possibly followed by arguments.
The commands are list below.
.IP \(bu
.B backup
makes a new backup.
The first time it is run, it makes a full backup,
after that an incremental one.
.IP \(bu
.B restore
is the opposite of a backup.
It copies backed up data from the backup repository to a target directory.
You can restore everything in a generation,
or just selected files.
Files to restore must be named using asbolute paths
(starting with /).
.IP \(bu
.B clients
lists the clients that are backed up to the repository.
.IP \(bu
.B generations
lists every backup generation for a given client,
plus some metadata about the generation.
.IP \(bu
.B genids
lists the identifier for every backup generation for a given client.
No other information is shown.
This can be useful for scripting.
.IP \(bu
.B ls
lists the contents of a given generation, similar to
.BR "ls \-lAR" .
.IP \(bu
.B kdirstat
lists the contents of a given generation, in a format which is
compatible with the
.BR "kdirstat"
cache file format, which can then be used to visualise the contents
of a backup.
.IP \(bu
.B verify
compares data in the backup with actual user data,
and makes sure they are identical.
It is most useful to run immediately after a backup,
to check that it actually worked.
It can be run at any time,
but if the user data has changed,
verification fails even though the backup is OK.
.IP \(bu
.B forget
removes backup generations that are no longer wanted,
so that they don't use disk space.
Note that after a backup generation is removed
the data can't be restored anymore.
You can either specify the generations to remove by listing them
on the command line,
or use the
.B \-\-keep
option to specify a policy for what to keep (everything else will
be removed).
.IP \(bu
.B fsck
checks the internal consistency of the backup repository.
It verifies that all clients, generations, directories, files, and
all file contents still exists in the backup repository.
It may take quite a long time to run.
.IP \(bu
.B force\-lock
removes lock files for aall clients in the repository.
You should only force a lock if you are sure no client is accessing
the repository.
A dangling lock might happen, for example,
if "obnam backup" loses its network connection to the backup repository.
.IP \(bu
.B client\-keys
lists the encryption key associated with each client.
.IP \(bu
.B list\-keys
lists the keys that can access the repository,
and which toplevel directories each key can access.
Some of the toplevel directories are shared between clients,
others are specific to a client.
.IP \(bu
.B list\-toplevels
is like
.BR list\-keys ,
but lists toplevels and which keys can access them.
.IP \(bu
.B add\-key
adds an encryption key to the repository.
By default, the key is added only to the shared toplevel directories,
but it can also be added to specific clients:
list the names of the clients on the command line.
They key is given with the
.B \-\-keyid
option.
Whoever has access to the secret key corresponding to the key id
can access the backup repository
(the shared toplevels plus specified clients).
.IP \(bu
.B remove\-key
removes a key from the shared toplevel directories,
plus any clients specified on the command line.
.IP \(bu
.B nagios\-last\-backup\-age
is a check that exits with non-zero return if a backup age exceeds a certain
threshold.  It is suitable for use as a check plugin for nagios.  Thresholds
can be given the
.B \-\-warn-age
and
.B \-\-critical-age
options.
.IP \(bu
.B diff
compares two generations and lists files differing between them. Every output
line will be prefixed either by a plus sign (+) for files that were added, a
minus sign (-) for files that have been removed or an asterisk (*) for files
that have changed.  If only one generation ID is specified on the command line
that generation will be compared with its direct predecessor. If two IDs have
been specified, all changes between those two generations will be listed.
.IP \(bu
.B mount
makes the backup repository available via a read-only FUSE filesystem.
Each backup generation is visible as a subdirectory,
named after the generation id.
This means you can look at backed up data using normal tools,
such as your GUI file manager,
or command line tools such as
.BR ls (1),
.BR diff (1),
and
.BR cp (1).
You can't make new backups with the mount subcommand,
but you can restore data easily.
.IP
You need to have the FUSE utilities and have permission to use FUSE
for this to work.
The details will vary between operating systems;
in Debian, install the package
.I fuse
and add yourself to the
.I fuse
group (you may need to log out and back in again).
.SS "Making backups"
When you run a backup,
.B obnam
uploads data into the backup repository.
The data is divided into chunks,
and if a chunk already exists in the backup repository,
it is not uploaded again.
This allows
.B obnam
to deal with files that have been changed or renamed since the previous
backup run.
It also allows several backup clients to avoid uploading the same data.
If,
for example, everyone in the office has a copy of the same sales brochures,
only one copy needs to be stored in the backup repository.
.PP
Every backup run is a
.IR generation .
In addition,
.B obnam
will make
.I checkpoint
generations every now and then.
These are exactly like normal generations,
but are not guaranteed to be a complete snapshot of the live data.
If the backup run needs to be aborted in the middle,
the next backup run can continue from the latest checkpoint,
avoiding the need to start over from scratch.
.PP
If one backup run drops a backup root directory,
the older generations will still keep it:
nothing changes in the old generations just because there is a new one.
If the root was dropped by mistake,
it can be added back and the next backup run will re-use the existing
data in the backup repository,
and will only back up the file metadata (filenames, permissions, etc).
.SS "Verifying backups"
What good is a backup system you cannot rely on?
How can you rely on something you cannot test?
The
.B "obnam verify"
command checks that data in the backup repository matches actual user data.
It retrieves one or more files from the repository and compares them to
the user data.
This is essentially the same as doing a restore,
then comparing restored files with the original files using
.BR cmp (1),
but easier to use.
.PP
By default, verification happens on all files.
You can also specify the files to be verified by listing them on the
command line.
You should specify the full paths to the files,
not relative to the current directory.
.PP
The output lists files that fail verification for some reason.
If you verify everything, it is likely that some files (e.g.,
parent directories of backup root) may have changed without it
being a problem.
Note that you will need to specify the whole path to the files
or directories to be verified, not relative to the backup root.
You still need to specify at least one of the backup roots
on the command line or via the
.B \-\-root
option so that obnam will find the filesystem, in case it is
a remote one.
.SS "URL syntax"
Whenever obnam accepts a URL, it can be either a local pathname,
or an
.B sftp
URL.
An sftp URL has the following form:
.IP
\fBsftp://\fR[\fIuser\fR@]\fIdomain\fR[:\fIport\fR]\fB/path
.PP
where
.I domain
is a normal Internet domain name for a server,
.I user
is your username on that server,
.I port
is an optional port number,
and
.I path
is a pathname on the server side.
Like
.BR bzr (1),
but unlike the sftp URL standard,
the pathname is absolute,
unless it starts with
.B /~/
in which case it is relative to the user's home directory on the server.
.PP
See the EXAMPLE section for examples of URLs.
.PP
You can use
.B sftp
URLs for the repository, or the live data (root),
but note that due to limitations in the protocol,
and its implementation in the
.B paramiko
library,
some things will not work very well for accessing live data over
.BR sftp .
Most importantly,
the handling of of hardlinks is rather suboptimal.
For live data access, you should not end the URL with
.B /~/
and should append a dot at the end in this special case.
.SS "Generation specifications"
When not using the latest generation,
you will need to specify which one you need.
This will be done with the
.B \-\-generation
option,
which takes a generation specification as its argument.
The specification is either the word
.IR latest ,
meaning the latest generation (also the default),
or a number.
See the
.B generations
command to see what generations are available,
and what their numbers are.
.SS "Policy for keeping and removing backup generations"
The
.B forget
command can follow a policy to automatically keep some and remove
other backup generations.
The policy is set with the
.BR \-\-keep =\fIPOLICY
option.
.PP
.I POLICY
is comma-separated list of rules.
Each rule consists of a count and a time period.
The time periods are
.BR h ,
.BR d ,
.BR w ,
.BR m ,
and
.BR y ,
for hour, day, week, month, and year.
.PP
A policy of
.I 30d
means to keep the latest backup for each day when a backup was made,
and keep the last 30 such backups.
Any backup matched by any policy rule is kept,
and any backups in between will be removed,
as will any backups older than the oldest kept backup.
.PP
As an example, assume backups are taken every hour, on the hour:
at 00:00, 01:00, 02:00, and so on, until 23:00.
If the
.B forget
command is run at 23:15, with the above policy,
it will keep the backup taken at 23:00 on each day,
and remove every other backup that day.
It will also remove backups older than 30 days.
.PP
If backups are made every other day, at noon,
.B forget
would keep the 30 last backups,
or 60 days worth of backups,
with the above policy.
.PP
Note that obnam will only inspect timestamps in the backup repository,
and does not care what the actual current time is.
This means that if you stop making new backups,
the existing ones won't be removed automatically.
In essence, obnam pretends the current time is just after the
latest backup when
.B forget
is run.
.PP
The rules can be given in any order,
but will be sorted to ascending order of time period before applied.
(It is an error to give two rules for the same period.)
A backup generation is kept if it matches any rule.
.PP
For example, assume the same backup frequency as above,
but a policy of
.IR 30d,52w .
This will keep the newest daily backup for each day for thirty days,
.I and
the newest weekly backup for 52 weeks.
Because the hourly backups will be removed daily,
before they have a chance to get saved by a weekly rule,
the effect is that the 23:00 o'clock backup for each day is
saved for a month,
and the 23:00 backup on Sundays is saved for a year.
.PP
If, instead, you use a policy of
.IR 72h,30d,52w ,
.B obnam
would keep the last 72 hourly backups,
and the last backup of each calendar day for 30 days,
and the last backup of each calendar week for 52 weeks.
If the backup frequency was once per day,
.B obnam
would keep the backup of each calendar hour for which a backup was made,
for 72 such backups.
In other words, it would effectively keep the last 72 daily backups.
.PP
Sound confusing?
Just think how confused the developer was when writing the code.
.PP
If no policy is given,
.B forget
will keep everything.
.PP
A typical policy might be
.IR 72h,7d,5w,12m ,
which means: keep
the last 72 hourly backups,
the last 7 daily backups,
the last 5 weekly backups and
the last 12 monthly backups.
If the backups are systematically run on an hourly basis,
this will mean keeping
hourly backups for three days,
daily backups for a week,
weekly backups for a month,
and monthly backups for a year.
.PP
The way the policy works is a bit complicated.
Run
.B forget
with the
.B \-\-pretend
option to make sure you're removing the right ones.
.\"
.SS "Using encryption"
.B obnam
can encrypt all the data it writes to the backup repository.
It uses
.BR gpg (1)
to do the encryption.
You need to create a key pair using
.B "gpg --gen-key"
(or use an existing one),
and then tell
.B obnam
about it using the
.B \-\-encrypt\-with
option.
You may optionally use a separate home directory using the
.B \-\-gnupghome
option. By default, the default directory for
.BR gpg(1)
will be used.
.SS "Configuration files"
.B obnam
will look for configuration files in a number of locations.
See the FILES section for a list.
All these files together are treated as one big file with the contents of all
files concatenated.
.PP
The files are in INI format,
and only the
.I [config]
section is used
(any other sections are ignored).
.PP
The long names of options are used as keys for configuration
variables.
Any setting that can be set from the command line
can be set in a configuration file,
in the
.I [config]
section.
.PP
For example, the options in the following command line:
.sp 1
.RS
obnam --repository=/backup --exclude='\.wav$' backup
.RE
.sp 1
could be replaced with the following configuration file:
.sp 1
.nf
.RS
[config]
repository: /backup
exclude: \.wav$
.RE
.fi
.sp 1
(You can use either
.I foo=value
or
.I foo: value
syntax in the files.)
.PP
The only unusual thing about the files is the way options that can be
used many times are expressed.
All values are put in a single logical line,
separated by commas
(and optionally spaces as well).
For example:
.sp 1
.RS
.nf
[config]
exclude = foo, bar, \\.mp3$
.fi
.RE
.sp 1
The above has three values for the
.B exclude
option:
any files that contain the words
.I foo
or
.I bar
anywhere in the fully qualified pathname,
or files with names ending with a period and
.I mp3
(because the exclusions are regular expressions).
.PP
A long logical line can be broken into several physical ones,
by starting a new line at white space,
and indenting the continuation lines:
.sp 1
.RS
.nf
[config]
exclude = foo,
    bar,
    \\.mp3$
.fi
.RE
.sp 1
The above example adds three exclusion patterns.
.SS "Multiple clients and locking"
.B obnam
supports sharing a repository between multiple clients.
The clients can share the file contents (chunks),
so that if client A backs up a large file,
and client B has the same file,
then B does not need to upload the large file to the repository a second time.
For this to work without confusion,
the clients use a simple locking protocol that allows only one client
at a time to modify the shared data structures.
Locks do not prevent read-only access at the same time:
this allows you to restore while someone else is backing up.
.PP
Sometimes a read-only operation happens to access a data structure at the
same time as it is being modified.
This can result in a crash.
It will not result in corrupt data,
or incorrect restores.
However, you may need to restart the read-only operation after a crash.
.\"---------------------------------------------------------------------
.SH OPTIONS
.SS "Option values"
The
.I SIZE
value in options mentioned above specifies a size in bytes,
with optional suffixes to indicate kilobytes (k), kibibytes (Ki),
megabytes (M), mebibyts (Mi), gigabytes (G), gibibytes (Gi),
terabytes (T), tibibytes (Ti).
The suffixes are case-insensitive.
.\" ------------------------------------------------------------------
.SH "EXIT STATUS"
.B obnam
will exit with zero if everything went well,
and non-zero otherwise.
.SH ENVIRONMENT
.B obnam
will pass on the environment it gets from its parent,
without modification.
It does not obey any unusual environment variables,
but it does obey the usual ones when running external programs,
creating temporary files, etc.
.SH FILES
.I /etc/obnam.conf
.br
.I /etc/obnam/*.conf
.br
.I ~/.obnam.conf
.br
.I ~/.config/obnam/*.conf
.RS
Configuration files for
.BR obnam .
It is not an error for any or all of the files to not exist.
.RE
.SH EXAMPLE
To back up your home directory to a server:
.IP
.nf
obnam backup \-\-repository sftp://your.server/~/backups $HOME
.PP
To restore your latest backup from the server:
.IP
.nf
obnam restore \-\-repository sftp://your.server/~/backups \\
\-\-to /var/tmp/my.home.dir
.PP
To restore just one file or directory:
.IP
.nf
obnam restore \-\-repository sftp://your.server/~/backups \\
\-\-to /var/tmp/my.home.dir $HOME/myfile.txt
.fi
.PP
Alternatively, mount the backup repository using the FUSE filesystem
(note that the
.B \-\-to
option is necessary):
.IP
.nf
mkdir my-repo
obnam mount \-\-repository sftp://your.server/~/backups \\
\-\-to my-repo
cp my-repo/latest/$HOME/myfile.txt
fusermount -u my-repo
.PP
To check that the backup worked:
.IP
.nf
obnam verify \-\-repository sftp://your.server/~/backups \\
/path/to/file
.PP
To remove old backups, keeping the newest backup for each day for
ten years:
.IP
.nf
obnam forget \-\-repository sftp://your.server/~/backups \\
\-\-keep 3650d
.PP
To verify that the backup repository is OK:
.IP
.nf
obnam fsck \-\-repository sftp://your.server/~/backups
.fi
.PP
To view the backed up files in the backup repository using FUSE:
.IP
.nf
obnam mount \-\-to my-fuse
ls -lh my-fuse
fusermount -u my-fuse
.fi
.SH "SEE ALSO"
.B obnam
comes with a manual in HTML and PDF forms.
See
.I /usr/share/doc/obnam
if you have Obnam installed system-wide,
or in the subdirectory
.I
manual
in the source tree.
.TP
.BR cliapp (5)