Current versions of XtraBackup (2.4.9 as of this writing), don't show arguments used. This is very helpful for knowing what exact command was used, by checking at the output only (which some times is the case in Support tickets).
This is what we get now:
[root@pxc-1 ~]# xtrabackup --backup --target-dir=/backups/
180122 21:03:31 version_check Connecting to MySQL server with DSN 'dbi:mysql:;mysql_read_default_group=xtrabackup' (using password: NO).
180122 21:03:31 version_check Connected to MySQL server
180122 21:03:31 version_check Executing a version check against the server...
180122 21:03:31 version_check Done.
180122 21:03:31 Connecting to MySQL server host: localhost, user: not set, password: not set, port: not set, socket: not set
Using server version 5.7.19-17-57
xtrabackup version 2.4.9 based on MySQL server 5.7.13 Linux (x86_64) (revision id: a467167cdd4)
xtrabackup: uses posix_fadvise().
xtrabackup: cd to /var/lib/mysql
xtrabackup: open files limit requested 0, set to 1024
xtrabackup: using the following InnoDB configuration:
xtrabackup: innodb_data_home_dir = .
xtrabackup: innodb_data_file_path = ibdata1:12M:autoextend
xtrabackup: innodb_log_group_home_dir = ./
xtrabackup: innodb_log_files_in_group = 2
xtrabackup: innodb_log_file_size = 50331648
InnoDB: Number of pools: 1
180122 21:03:31 >> log scanned up to (13891914)
xtrabackup: Generating a list of tablespaces
InnoDB: Allocated tablespace ID 21 for sys/sys_config, old maximum was 0
180122 21:03:32  Copying ./ibdata1 to /backups/ibdata1
180122 21:03:32  ...done
If I'm not mistaken, innobackupex used to output them at the beginning, which was really helpful.