Useful Commands in Linux and centos
  /home full issue(creating disk space)     find /home/*/ -name .trash | xargs rm -rf      ==================   changing permission for file only     find . -type f -exec chmod 644 {} \;     for directory   find . -type d -exec chmod 775 {} \;       find /home/*/public_html -iname '*.mp3' -exec mv "{}" /home/delete \;    find /home/*/public_html -iname 'backup-' -exec mv "{}" /home/delete \;    ==================   How  know the hard drive speed   ( this will check how fast the sites are resoving also)   Use /dev/hda or /dev/sda or what ever is the drive in the server:   hdparm -tT /dev/hda   This command will show results like:   /dev/hda:  Timing cached reads:   8808 MB in  2.00 seconds = 4406.87 MB/sec  Timing buffered disk reads:  162 MB in  3.03 seconds =  53.44 MB/sec   If the second measurement is under 40MB/sec, the server is too slow and needs a hardware checkup   Monitoring the system:      Basic command line:       pstree       Pro...