Top command redirection - shell

Question

I am trying to analyse a randomly crashing application.To get some details of the process i am implementing a script like below
procID=$(ps -aef|grep app|awk '{print $2}')
top -p $procID -b -d 10 > test.log
In this case top command will execute for every 10 sec and write to test.log. Planning to run it indefinitely, but I want to flush out the contents of test.log each time top command writes some value to it. How can I modify the script accordingly ?

Answer 1

To avoid your log getting too big, I suggest you use logrotate instead. In short, logrotate creates a cronjob that will "rotate" your log file upon a condition (one file per day, rotate when the file reaches a given size, etc.). You can also choose to keep the X last rotated logs.
This is what is used for lastmessage and the other linux log files (hence the .log.1, .log.2 etc.)
Here is a basic way to make it work:
Create a configuration for your file in /etc/logrotate.d. For example:
# /etc/logrotate.d/test
/var/log/test.log {
size 4M
create 770 somegroup someuser
rotate 4
missingok
copytruncate
}
What it says:
size 4M: rotate file after it reaches 4M in size
create ...: create new file with the given permisions (replace somegroup someuser by your usergroup and username)
rotate 4: keep the last 4 log files (test.log, test.log.1 etc)
missingOk an copyTruncate: avoid some errors (see the doc for more info)
Check that your file is correct by executing:
sudo logrotate /etc/logrotate.d/test
enjoy.
More about logrotate: https://support.rackspace.com/how-to/understanding-logrotate-utility/