I have recently installed a two node RAC version 18.104.22.168 on top of RedHat 7.2 and few hours after the initial setup I started experiencing ASM and database crashes.
Checking in the alert log I found the following errors:
Tue Oct 04 05:25:17 2016 Dumping diagnostic data in directory=[cdmp_20161004052517], requested by (instance=1, osid=84872 (MMAN)), summary=[abnormal instance termination]. Tue Oct 04 05:25:18 2016 Instance terminated by USER, pid = 84872 Tue Oct 04 05:25:18 2016 Errors in file /oams/base/diag/rdbms/txdop/txdop1/trace/txdop1_mman_84872.trc: ORA-27300: OS system dependent operation:semctl failed with status: 22 ORA-27301: OS failure message: Invalid argument ORA-27302: failure occurred at: sskgpwrm1 ORA-27157: OS post/wait facility removed ORA-27300: OS system dependent operation:semop failed with status: 43 ORA-27301: OS failure message: Identifier removed ORA-27302: failure occurred at: sskgpwwait1
The errors pointed to the OS and in particular to the possibility that semaphores in use by Oracle have been removed.
Because this is a fresh installation and I was the only person using the cluster, it was easy to exclude any third party activity. Then I double-checked the kernel parameters and all other system pre-requisites without finding any wrong configuration.
Finally, on MOS and I found the followinfg note “ALERT: Setting RemoveIPC=yes on Redhat 7.2 Crashes ASM and Database Instances as Well as Any Application That Uses a Shared Memory Segment (SHM) or Semaphores (SEM) (Doc ID 2081410.1)”
Redhat 7.2, systemd-logind service introduced a new feature to remove all IPC objects when a user fully logs out.
The feature is controled by the option RemoveIPC in the /etc/systemd/logind.conf configuration file, see man logind.conf(5) for details.
The default value for RemoveIPC in RHEL7.2 is yes.
As a result, when the last oracle or grid user disconnects, the OS removes shared memory segments and semaphores for those users.
As Oracle ASM and Databases use shared memory segments for SGA, removing shared memory segments will crash the Oracle ASM and database instances.