innobackupexでsocketエラーが出て詰まったのでメモ

以下を打つとsocketエラーが出る
$ innobackupex --ibbackup=xtrabackup --defaults-file=/etc/my.cnf --user=root --password=xxx hoge

エラー内容

InnoDB Backup Utility v1.5.1-xtrabackup; Copyright 2003, 2009 Innobase Oy
and Percona LLC and/or its affiliates 2009-2013.  All Rights Reserved.

This software is published under
the GNU GENERAL PUBLIC LICENSE Version 2, June 1991.

Get the latest version of Percona XtraBackup, documentation, and help resources:
http://www.percona.com/xb/p

151007 13:59:18  innobackupex: Executing a version check against the server...
151007 13:59:18  innobackupex: Connecting to MySQL server with DSN 'dbi:mysql:;mysql_read_default_file=/etc/my.cnf;mysql_read_default_group=xtrabackup' as 'root'  (using password: YES).
innobackupex: got a fatal error with the following stacktrace: at /usr/bin/innobackupex line 3011.
        main::mysql_connect('abort_on_error', 1) called at /usr/bin/innobackupex line 1551
innobackupex: Error: Failed to connect to MySQL server: DBI connect(';mysql_read_default_file=/etc/my.cnf;mysql_read_default_group=xtrabackup','root',...) failed: Can't connect to local MySQL server through socket '/var/lib/mysql/mysql.sock' (2) at /usr/bin/innobackupex line 2995.
151007 13:59:18  innobackupex: Connecting to MySQL server with DSN 'dbi:mysql:;mysql_read_default_file=/etc/my.cnf;mysql_read_default_group=xtrabackup' as 'root'  (using password: YES).
innobackupex: got a fatal error with the following stacktrace: at /usr/bin/innobackupex line 3011.
        main::mysql_connect('abort_on_error', 1) called at /usr/bin/innobackupex line 1570
innobackupex: Error: Failed to connect to MySQL server: DBI connect(';mysql_read_default_file=/etc/my.cnf;mysql_read_default_group=xtrabackup','root',...) failed: Can't connect to local MySQL server through socket '/var/lib/mysql/mysql.sock' (2) at /usr/bin/innobackupex line 2995.

対処法

オプション--hostを設定する。
ローカル・ループバック・アドレスを設定したらinnobackupexが使えるようになった。
$ innobackupex --ibbackup=xtrabackup --defaults-file=/etc/my.cnf --user=root --password=xxx --host=127.0.0.1 hoge