General Solutions of ORA-12547: TNS: lost contact

In the post Troubleshoot ORA-12547: TNS: lost contact it is already discussed about the specific causes and solutions of ORA-12547: TNS: lost contact. If you don't have those specific scenarios then this post will provide you general solutions for error ORA-12547 which might help you to avoid this error.

1. Verify that environmental variable ORACLE_HOME, ORACLE_SID, PATH, LD_LIBRARY_PATH are correct.

$ echo $ORACLE_HOME
$ echo $ORACLE_SID
$ echo $LD_LIBRARY_PATH
$ echo $PATH

2. On AIX, HP-UX, Linux, MacOSX, Solaris, Tru64 system make sure kernel parameters settings are ok. To set, check and modify your kernel parameters have a look at the post How to check and modify Kernel Parameters in Linux
and Install Oracle on Linux.

3. There may have incorrect permissions on the ORACLE.exe
The 'ls' command should show permissions 6751 (as follows)

$ cd $ORACLE_HOME/bin
$ ls -l oracle

The output should be
-rwsr-s--x 1 oracle dba

If not then please execute the following
$ chmod 6751 oracle

4. Check whether current ulimit settings is ok.
$ ulimit -a

A sample output is,

$ ulimit -a 
    core file size        (blocks, -c) unlimited 
    data seg size         (kbytes, -d) unlimited 
    file size             (blocks, -f) unlimited 
    open files                    (-n) 256 
    pipe size          (512 bytes, -p) 10 
    stack size            (kbytes, -s) 8192 
    cpu time             (seconds, -t) unlimited 
    max user processes            (-u) 29995 
    virtual memory        (kbytes, -v) unlimited 

If open files (-n) is set to lower then make it unlimited or set it to a higher value, for example:
$ulimit -n 4096

5. Check the permission on the library files under $ORACLE_HOME/lib and $ORACLE_HOME/lib32 are ok. Since since sqlplus and other binaries require these libraries so if sqlplus does not have permission on these file it may throw ORA-12517: TNS: lost contact. It should have 755 on unix system.

You can give 755 permissions to $ORACLE_HOME/lib and $ORACLE_HOME/lib32
$ chmod -R 755 $ORACLE_HOME/lib
$ chmod -R 755 $ORACLE_HOME/lib32
$ cd $ORACLE_HOME/bin
$ relink all