NFS mount options for Oracle database

OEM 12c job failed to create standby database for Oracle 10.2 on Oracle Linux.
NFS mounted staging area is used.
Production database alert log shows
ALTER DATABASE CREATE STANDBY CONTROLFILE AS '/mnt/software/oracle_CCASEPRD_linux/CCASEPRD_43/CONTROL_FILE_BACKUP_STANDBY_NO_RECOVERY'

ORA-00494: enqueue [CF] held for too long (more than 900 seconds) by 'inst 1, osid 2944'

which is also confirmed by SQLPLUS running the same command.

The problem is solved by using nolock option for NFS mount.

The following NFS options are successful:

rw,bg,hard,nointr,rsize=32768,wsize=32768,tcp,nolock,vers=3,timeo=600

Useful info on Oracle Support:
Mount Options for Oracle files when used with NFS on NAS devices (Doc ID 359515.1)
Howto Optimize NFS Performance with NFS options. (Doc ID 397194.1)
Poor Performance of APPS 11i or 12 When Using Shared APPL_TOP with NAS (Doc ID 802704.1)

OEM 12c Named Credentials - SSH Key Credentials

The following commands can be used on OMS host to configure SSH connection from OMS host to target host. Check/backup authorized_keys on OMS host. sshUserSetup.sh overwrites authorized_keys instead of just adding public key (it created backup though authorized_keys.tmp).
cd /oui/prov/resources/scripts
sshUserSetup.sh -setup -user -hosts

Alternately (if you do not have password for oracle on target host) generate SSH keys on OMS host with ssh-keygen and add id_rsa.pub to authorized_keys on target host (/home/oracle/.ssh) using root or sudo.

Then in OEM navigate to Setup > Security > Named Credentials

and create New Credential with Credential Type = SSH Key Credentials, using private/public keys from OMS host.