This problem only exists from MariaDB 10.1.5 through 10.1.18

One work around for this problem is to install the "which" package:

[root@node2 ~]# yum install -y which
[...]
[root@node2 ~]# systemctl restart mariadb

Then everything works fine.

Maybe a better solution might be to include "Requires: which" in either the MariaDB-server or galera rpm spec file.

I just upgraded to MariaDB 10.1.19 and when I try to enable "wsrep_on=ON" I'm still unable to start the server due to the following error:

2016-11-08 13:12:58 140186172258048 [Note] WSREP: Flow-control interval: [32, 32]
2016-11-08 13:12:58 140186172258048 [Note] WSREP: Shifting OPEN -> PRIMARY (TO: 6967208)
2016-11-08 13:12:58 140186526259968 [Note] WSREP: State transfer required:
Group state: 08c1571e-8956-11e6-b83e-c7f185019621:6967208
Local state: 08c1571e-8956-11e6-b83e-c7f185019621:6967167
2016-11-08 13:12:58 140186526259968 [Note] WSREP: New cluster view: global state: 08c1571e-8956-11e6-b83e-c7f185019621:6967208, view# 91: Primary, number of nodes: 4, my index: 3, protocol version 3
2016-11-08 13:12:58 140186526259968 [Warning] WSREP: Gap in state sequence. Need state transfer.
2016-11-08 13:12:58 140186147092224 [Note] WSREP: Running: 'wsrep_sst_rsync --role 'joiner' --address '192.168.71.100' --datadir '/var/lib/mysql/' --parent '4202' --binlog 'mysql-binlog' '
/usr//bin/wsrep_sst_common: line 120: which: command not found
2016-11-08 13:12:59 140186147092224 [ERROR] WSREP: Failed to read 'ready <addr>' from: wsrep_sst_rsync --role 'joiner' --address '192.168.71.100' --datadir '/var/lib/mysql/' --parent '4202' --binlog 'mysql-binlog'
Read: '(null)'
2016-11-08 13:12:59 140186147092224 [ERROR] WSREP: Process completed with error: wsrep_sst_rsync --role 'joiner' --address '192.168.71.100' --datadir '/var/lib/mysql/' --parent '4202' --binlog 'mysql-binlog' : 2 (No such file or directory)
2016-11-08 13:12:59 140186526259968 [ERROR] WSREP: Failed to prepare for 'rsync' SST. Unrecoverable.
2016-11-08 13:12:59 140186526259968 [ERROR] Aborting

Error in my_thread_global_end(): 1 threads didn't exit
161108 13:13:07 mysqld_safe mysqld from pid file /var/log/mysqld/mysqld.pid ended