I am getting below error when starting the xampp in linux system,

[(20014)Internal error: Error retrieving pid file logs/httpd.pid
Remove it before continuing if it is corrupted.]

You can easily fix this error, just follow the steps,
stop the xampp :
local@host# /opt/lampp/lampp stop

open lampp logs directory and move or remove the httpd.pid file and start the xampp
localhost~]#  cd /opt/lampp/logs

[localhost~]#  mv httpd.pid  httpd_pid_bak
[localhost~]#  rm httpd.pid     

[root@local]# /opt/lampp/lampp start
Starting XAMPP for Linux 1.8.2-3...
XAMPP: Starting Apache...ok.
XAMPP: Starting MySQL...ok.
XAMPP: Starting ProFTPD...ok.

Type in the the URL on your web browser:  http://localhost

If you are getting same error when starting apache do follow steps,

1.    Find the apache logs directory (If you have installed the apache under  /usr/local/ directory )
local@host # cd  /usr/local/apache/logs

2.   move or remove the httpd.pid file and start apache
local@host # mv httpd.pid   httpd.pid_bak
local@host # /etc/init.d/httpd start
local@host # /etc/init.d/httpd status

apache service is working fine...