backup fails with 'error: unknown argument'

i am using xtrabackup for the first time here, to backup a mysql server on fedora 20.
i only have xtrabackup installed and no other percona packages, presently.

i ran:

innobackupex --user=root --password=mypassword /my/path/to/backups

plus also ran it a 2nd time using sudo.

in both cases, errors were shown in the terminal log.

the 2nd one (using sudo) produced:

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:

141107 22:28:24 innobackupex: Connecting to MySQL server with DSN 'dbi:mysql:;mysql_read_default_group=xtrabackup' as 'root' (using password: YES).
141107 22:28:24 innobackupex: Connected to MySQL server
141107 22:28:24 innobackupex: Executing a version check against the server...
141107 22:28:24 innobackupex: Done.
141107 22:28:24 innobackupex: Starting the backup operation

IMPORTANT: Please check that the backup run completes successfully.
At the end of a successful backup run innobackupex
prints "completed OK!".

innobackupex: Using server version 5.5.38

innobackupex: Created backup directory /my/path/to/backups/2014-11-07_22-28-24

141107 22:28:24 innobackupex: Starting ibbackup with command: xtrabackup --defaults-group="mysqld" --backup --suspend-at-end --target-dir=/my/path/to/backups/2014-11-07_22-28-24 --innodb_log_file_size="5242880" --innodb_data_file_path="ibdata1:10M:autoextend" --tmpdir=/var/tmp --extra-lsndir='/var/tmp'
innobackupex: Waiting for ibbackup (pid=11022) to suspend
innobackupex: Suspend file '/my/path/to/backups/2014-11-07_22-28-24/xtrabackup_suspended_2'

xtrabackup: Error: unknown argument: 'dev/2014-11-07_22-28-24'
innobackupex: got a fatal error with the following stacktrace: at /bin/innobackupex line 2694.
main::wait_for_ibbackup_file_create('/my/path/to/backups/2014-11-07_22-28-24/xtr...') called at /bin/innobackupex line 2714
main::wait_for_ibbackup_suspend('/my/path/to/backups/2014-11-07_22-28-24/xtr...') called at /bin/innobackupex line 1968
main::backup() called at /bin/innobackupex line 1592
innobackupex: Error: The xtrabackup child process has died at /bin/innobackupex line 2694.

can anyone decode this for me? i have not been able to figure out what the cause of the problem is yet.