# Configure xtrabackup

All the xtrabackup configuration is done through options, which behave
exactly like standard MySQL program options: they can be specified either at
the command-line, or through a file such as `/etc/my.cnf`.

The xtrabackup binary reads the `mysqld` and `xtrabackup` sections
from any configuration files, in that order. That is so that it can read its
options from your existing MySQL installation, such as the datadir or
some InnoDB options. If you want to override these options specify them
in the `xtrabackup` section. These options are read at a later time and take
precedence.

You don’t need to put any configuration in your `my.cnf` if you don’t
want to. You can simply specify the options on the command-line. Normally, the
only thing you might find convenient to place in the `xtrabackup` section
of your `my.cnf` file is the `target_dir` option to default the
directory in which the backups will be placed, for example:

```
[xtrabackup]
target_dir = /data/backups/mysql/
```

This manual will assume that you do not have any file-based configuration for
xtrabackup, so it will always show command-line options being used
explicitly. Please see the option and variable reference for details on all the configuration options.

The xtrabackup binary does not accept exactly the same syntax in the
`my.cnf` file as the mysqld server binary does. For historical
reasons, the mysqld server binary accepts parameters with a
`--set-variable=<variable>=<value>` syntax, which xtrabackup does not
understand. If your `my.cnf` file has such configuration directives, you
should rewrite them in the `--variable=value` syntax.

## System configuration and NFS volumes

The xtrabackup tool requires no special configuration on most systems. However, the storage where the `--target-dir` is located must behave properly when `fsync()` is called. In particular, we have noticed that if you mount the NFS volume without the `sync` option the NFS volume does not sync the data. As a result, if you back up to an NFS volume mounted with the async option, and then try to prepare the backup from a different server that also mounts that volume, the data might appear to be corrupt. You can use the `sync` mount option to avoid this problem.