ORA-12547: TNS: lost contact error Solution

Running Environment: Ubuntu + Oracle 11.2.0
 
ORA-12547: TNS: lost contact error occurs when the command starts oracle. Good afternoon, no matter in the afternoon. If the link is invalid, it will not work after Shutdown and restart. Then google found the solution below. In retrospect, the cause is the permission problem. At noon, I accidentally assigned the permission to the folder of the oracle installation directory. It seems that the permission of oracle cannot be changed at will.

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Cause

1. This cocould be due to kernel parameters settings
2. Incorrect permissions on the ORACLE executable
 
Solution
 
To implement the solution, please execute the following steps:
 
1.
This cocould be due to kernel parameters settings
Please check the notes below that provide the required settings for kernel parameters
Note 169706.1 Oracle Database on AIX, HP-UX, Linux, MacOSX, Solaris, Tru64
Note 201021.1 SOLARIS: Quick Start Guide-9.2.0 RDBMS Installation
 
2.
This cocould be due to Incorrect permissions on the ORACLE.exe
The 'LS' command shocould show permissions 6751 (as follows)
 
Please check the following:
 
$ Cd $ ORACLE_HOME/bin
$ Ls-l oracle
 
The output shocould be
-Rwsr-s -- x 1 oracle dba
 
If not then please execute the following
$ Chmod 6751 oracle
 
Please also verify if the following are correct
 
Echo $ ORACLE_HOME
Echo $ ORACLE_SID
Echo $ LD_LIBRARY_PATH
Echo $ PATH
 
3.
If the above does not resolve I suggest that you shutdown the database and listener and then
"Relink all"
Note 131321.1 How to Relink Oracle Database Software on UNIX
After completing the preceding steps, it is OK to start oracle again.