Error: SP2-0667: Message file sp1<lang>.msb not found

[oracle@localhost bin]$ ./sqlplus
Error 6 initializing SQL*Plus
SP2-0667: Message file sp1<lang>.msb not found
SP2-0750: You may need to set ORACLE_HOME to your Oracle software directory
[oracle@localhost bin]$ 

Solution: Export the Oracle_home variable in Linux Environment will fix the issue

[oracle@localhost bin]$ export ORACLE_BASE=/u01/app/oracle
[oracle@localhost bin]$ export ORACLE_HOME=$ORACLE_BASE/product/19c/dbhome_1
[oracle@localhost bin]$ export ORACLE_SID=orcl
[oracle@localhost bin]$ export PATH=$PATH:$ORACLE_HOME/bin