Error : Shared Memory realm while opening db

Issue of Shared Memory realm faced while starting the db 11.1.0.7  installed on HP-UX 11.31

I changed the OS kernel parameter as hostname length is =8 characters so I changed the

expanded_node_host_names=1 so that hostname length will be increased from 8 -64 characters.

And did sytem restart. But while opening the database I got Shared memory realm error.

SQL> startup
Assertion failed: uname(&name) >= 0, file snlrn.c, line 395
ORA-03113: end-of-file on communication channel
SQL> shutdown immediate
ORA-01033: ORACLE initialization or shutdown in progress
SQL> startup
ORA-27100: shared memory realm already exists
HPUX-ia64 Error: 17: File exists

The uname_eoverflow kernel parameter is by default set to 1 and when I changed the expanded_node_host_names value to 1 we started facing the above issue.

If anyone takes a first look on this error, it seems that there is still shared memory occupied by previous Oracle Sessions and try to clean it up using ipcs and ipcrm commands.

uname_eoverflow: The setting of this boolean parameter determines what happens when uname gets a long hostname (and it isn't set up for long hostnames). If this kernel tunable is true (1), then generate an error EOVERFLOW; if the tunable is false (0), then silently truncate the host name before returning it in the uname system call.

expanded_node_host_names: The setting of this boolean parameter affects whether long host names (and node names) are supported. If this tunable is set to true (1), then the host and node names can be up to 255 characters (actually, 255 bytes); if set to false (0), then the limits are 8 bytes and 64 bytes for the host and node names respectively. The actual current host name (or node name) is unaffected, no matter the setting.

If both parameter values will be 1 then they will conflict each other and it will create issue to resolve HOSTNAME, which in our case was happening.

So afterwards when we changed the parameter value of uname_eoverflow to 0, above issue resolved and our database and application started smoothly.