#ORACLE
export ORACLE_BASE=/oracle18c/app/oracle
export ORACLE_HOME=$ORACLE_BASE/product/18.0.0/dbhome_1
export PATH=/usr/sbin:/usr/local/bin:$PATH
export PATH=$ORACLE_HOME/bin:$PATH
export LD_LIBRARY_PATH=$ORACLE_HOME/lib:/lib:/usr/lib:/usr/local/lib
export ORACLE_LIBPATH=$ORACLE_HOME/lib
export CLASSPATH=$ORACLE_HOME/jlib:$ORACLE_HOME/rdbms/jlib:$CLASSPATH
export ORACLE_HOSTNAME=$HOSTNAME
export ORA_INVENTORY=/oracle18c/app/oraInventory
export DATA_DIR=$ORACLE_BASE/oradata
export TNS_ADMIN=$ORACLE_HOME/network/admin
export ADR_HOME=$ORACLE_BASE/diag
#--------------------------------------------------------------------
export ORACLE_SID=orcl
export ORACLE_UNQNAME=orcl
export PDB_NAME=pdb
export NLS_LANG=AMERICAN_AMERICA.AL32UTF8
#--------------------------------------------------------------------
export TMP=/tmp; export TMPDIR=$TMP; export TEMP=$TMP

oracle@sergey-Bionic:~$ lsnrctl status

LSNRCTL for Linux: Version 18.0.0.0.0 - Production on 25-APR-2019 17:35:43

Copyright (c) 1991, 2018, Oracle.  All rights reserved.

Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=sergey-Bionic)(PORT=1521)))
STATUS of the LISTENER
------------------------
Alias                     LISTENER
Version                   TNSLSNR for Linux: Version 18.0.0.0.0 - Production
Start Date                25-APR-2019 16:50:53
Uptime                    0 days 0 hr. 44 min. 49 sec
Trace Level               off
Security                  ON: Local OS Authentication
SNMP                      OFF
Listener Parameter File   /oracle18c/app/oracle/product/18.0.0/dbhome_1/network/admin/listener.ora
Listener Log File         /oracle18c/app/oracle/diag/tnslsnr/sergey-Bionic/listener/alert/log.xml
Listening Endpoints Summary...
  (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=sergey-Bionic)(PORT=1521)))
  (DESCRIPTION=(ADDRESS=(PROTOCOL=ipc)(KEY=EXTPROC1521)))
The listener supports no services
The command completed successfully
oracle@sergey-Bionic:~$ ss -elpunt | grep -E "^Net|tnslsnr"
Netid  State    Recv-Q   Send-Q      Local Address:Port      Peer Address:Port
tcp    LISTEN   0        128                     *:1521                 *:*      users:(("tnslsnr",pid=3394,fd=8)) uid:54321 ino:39696 sk:12 v6only:0 <->
oracle@sergey-Bionic:~$

oracle@sergey-Bionic:/$ strace -f -o /tmp/strace.log $ORACLE_HOME/bin/sqlplus /nolog

SQL*Plus: Release 18.0.0.0.0 - Production on Thu Apr 25 18:02:09 2019
Version 18.3.0.0.0

Copyright (c) 1982, 2018, Oracle.  All rights reserved.

SQL> connect sys/oracle18c as sysdba;
ERROR:
ORA-12547: TNS:lost contact


SQL>