Find command related to  mtime:

find $HOME -mtime 0

Search  for  files in your home directory which have been modified in the last twenty-four hours.  This command 
works this way because the time since each file was last modified is divided by 24 hours and any  remainder  is
discarded.   That  means  that  to match -mtime 0, a file will have to have a modification in the past which is
less than 24 hours ago

2014-04-09 10:00:00  (time difference / 24 and any remainder is discarded)

find -mtime 0 time is from  2014-04-08 10:00:00 (not included) to 2014-04-09 10:00:00(included)
find -mtime 1 time is from  2014-04-07 10:00:00 (not included) to 2014-04-08 10:00:00 (included)

find -mtime +0 time is before 2014-04-08 10:00:00(included)
find -mtime +1 time is before 2014-04-07 10:00:00(included)
find -mtime -1 time is after 2014-04-07 10:00:00 (not included)
 ps -caefL | grep RT <======get all thread info including running level 




ls /etc/localtime  <===check local time configuration, the os log use this time zone
ln -s /usr/share/zoneinfo/PST&PDT /etc/localtime  <==change to PST&PDT
top -Hb -n 1 -p  <==top command to show every thread


sed -n '1,2p' 1.txt <===choose 1 to 2 line to print
sed -i '1,2d' 1.txt <===delete the 1 to 2 line in 1.txt
A=$(sed -n '$=' /tmp/1.txt)  <===count the line number of the file
sed -i $(($A-n+1)),${A}d /tmp/1.txt <===delete from the end

split -l line_number /tmp/1.txt <===split a big file to a lot of small files, however, keep the original file
                                <===If the file is really huge, use hadoop is a good idea