ORA-21561: OID generation failed

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General
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sqlplus is giving an error:
my_user@ip:>% sqlplus system/sys_pass@orainst

SQL*Plus: Release 11.2.0.4.0 Production on Thu Jul 19 19:02:16 2018

Copyright (c) 1982, 2013, Oracle.  All rights reserved.

ERROR:
ORA-21561: OID generation failed

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Investigation
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Findings:

A.  Linux prompt has changed 

from: my_user@srv-020-app-009

to:      my_user@ip:

B. tnsping is working fine:

my_user@ip: tnsping orainst

TNS Ping Utility for Linux: Version 11.2.0.4.0 - Production on 19-JUL-2018 19:02:10

Copyright (c) 1997, 2013, Oracle.  All rights reserved.

Used parameter files:
/software/oracle/112/network/admin/sqlnet.ora


Used TNSNAMES adapter to resolve the alias
Attempting to contact (DESCRIPTION = (ADDRESS_LIST = (ADDRESS = (PROTOCOL = TCP)(HOST = 100.200.220.230)(PORT = 1521))) (CONNECT_DATA = (SERVER = DEDICATED) (SERVICE_NAME = otainst)))
OK (10 msec)

But sqlplus is giving an error:
my_user@ip:>% sqlplus system/sys_path@orainst

SQL*Plus: Release 11.2.0.4.0 Production on Thu Jul 19 19:02:16 2018

Copyright (c) 1982, 2013, Oracle.  All rights reserved.

ERROR:
ORA-21561: OID generation failed

/etc/hosts
Checking /etc/hosts - that file was not changed for a very long time
What might be the issue?


~root/.bash_history
Checking for suspicious commands inside ~root/.bash_history.
There is this command:

hostname ip

revert that setup by:

hostname srv-020-app-009

Now Linux hostname of the client, is matching the hostname inside /etc/hosts/

# Do not remove the following line, or various programs
# that require network functionality will fail.
::1             localhost6.localdomain6 localhost6
127.0.0.1       localhost.localdomain localhost
100.200.220.230 srv-020-app-009 

Now the prompt in Linux is correct.

And sqlplus is working fine.