Permissions confusion when executing binaries via script

ls -al /home/dmsinst1/sqllib/adm/db2start -r-sr-sr-x 1 root dmsiadm1 93613 Jun 26 14:14 /home/dmsinst1/sqllib/adm/db2start ls -al /home/bpminst1/sqllib/adm/db2start -r-sr-sr-x 1 root bpmiadm1 93613 Jun 26 14:15 /home/bpminst1/sqllib/adm/db2start groups dmsinst1 dmsinst1 : dmsiadm1 groups bpminst1 bpminst1 : bpmiadm1 So, when running the following script as root: #!/bin/bash su bpminst1 -c "/home/bpminst1/sqllib/adm/db2start" su dmsinst1 -c "/home/dmsinst1/sqllib/adm/db2start" I get: [root@dmsnl857-vm ~]# ./startAll.sh SQL1092N The requested command or operation failed because the user ID does not have the authority to perform the requested command or operation. User ID: "BPMINST1". 06/29/2017 09:16:03 0 0 SQL1063N DB2START processing was successful. SQL1063N DB2START processing was successful. The second command is apparently executed without errors. **update**: with set -x [root@dmsnl857-vm ~]# ./startAll.sh + echo 'Starting BPM DB2 instance ... ' Starting BPM DB2 instance ... + su bpminst1 -c /home/bpminst1/sqllib/adm/db2start SQL1092N The requested command or operation failed because the user ID does not have the authority to perform the requested command or operation. User ID: "BPMINST1". + echo 'Starting DMS DB2 instance ... ' Starting DMS DB2 instance ... + su dmsinst1 -c /home/dmsinst1/sqllib/adm/db2start 06/29/2017 09:44:13 0 0 SQL1063N DB2START processing was successful. SQL1063N DB2START processing was successful.