A better script to kill CrashPlan when it starts using too much RAM because it’s a Java app

In a recent post about using CrashPlan for backup but getting the java process to behave, I said to create a file named kill_java_mem.sh in ~/bin/cronjobs & put the following in it:

#!/bin/bash

# Figure out how much RAM Java is using
# Uses the RSS column of ps (#6)
# RSS = the real memory (resident set) size of the process (in 1024 byte units)
javamem="$(ps aux | grep java | grep root | awk -F' ' '{print $6}')"

# Get Java’s PID (2nd column of ps)
javapid="$(ps aux | grep java | grep root | awk -F' ' '{print $2}')"

# If Java is using over 200 MB of RAM, kill the process
if [ $javamem gt 204800 ]
then
  kill $javapid
fi

After thinking about it, I decided that this script was seriously flawed due to a couple of stupid things I overlooked.

First, what if there’s more than one java process? My script just assumes there’s one. Actually, I only care about one at this point, since I only have one app on my Mac that uses Java: CrashPlan. Even so, the script should be rewritten to reflect this.

Second, CrashPlan is configured to run from 5 p.m. to 9 a.m., which is fine. While I’m awake from 5 p.m. to about 1 a.m., it’s OK for CrashPlan to run, but I don’t want the java process to use more than 200 MB of RAM during that time. After 1 a.m. & until I wake up, it’s OK for Java to use more than 200 MB of RAM while CrashPlan backs things up overnight.

In other words, here’s the breakdown of what I want by time:

• 9 a.m.–5 p.m.: CrashPlan shouldn’t run, & java processes should not use more than 200 MB of RAM
• 5 p.m.–1 a.m.: CrashPlan should run, but java processes should not use more than 200 MB of RAM
• 1 a.m.–9 a.m.: CrashPlan should run, & java processes can use more than 200 MB of RAM

How to do that with my script? If I was using cron to manage when my script ran, I can just tell cron when to run the script & it would be over & done with. Unfortunately, while cron is still present in Mac OS X, it’s deprecated, & on top of that, while on my Mac I try to do things the Mac way. That means launchd, & launchd doesn’t allow you specify a range of time during which things should run. That means you have to set the time span in your script.¹

Here’s the newly written script that takes the two issues into account. Notice that I’m now looking specifically for the CrashPlan PID & I’m only killing the java process during a specific time span:

#!/bin/bash

# Figure out how much RAM Java is using
# Uses the RSS column of ps (#6)
# RSS = the real memory (resident set) size of the process (in 1024 byte units)
javamem="$(ps aux | grep java | grep CrashPlan | awk -F' ' '{print $6}')"

# Get Java’s PID (2nd column of ps)
javapid="$(ps aux | grep java | grep CrashPlan | awk -F' ' '{print $2}')"

# Get current time
currenttime="$(date +%H%M)"

# If Java is using over 200 MB of RAM …
if [ $javamem -gt 204800 ] ; then 
  # … & if it’s between 1 & 9 a.m., then do nothing
  if [ $currenttime -gt 0100 ] && [ $currenttime -lt 0900 ] ; then
    sleep 3
  else
# … but if it’s NOT between 1 & 9 a.m., then kill the java process
kill $javapid
  fi
fi

That works, but it could be better. My good buddy Robert Citek suggested this instead:

#!/bin/bash

# Figure out how much RAM Java is using
# Uses the RSS column of ps (#6)
# RSS = the real memory (resident set) size of the process (in 1024 byte units)
javamem="$(ps aux | grep java | grep CrashPlan | awk -F' ' '{print $6}')"

# Get Java’s PID (2nd column of ps)
javapid="$(ps aux | grep java | grep CrashPlan | awk -F' ' '{print $2}')"

# Get current time
currenttime="$(date +%H%M)"

# If Java is using over 200 MB of RAM & it’s not between 1 & 9 a.m., kill it
if [ $javamem -gt 204800 ] && ( [ $currenttime -lt 0100 ] || [ $currenttime -gt 0900 ] ) ; then
  kill $javapid
fi

Just to review:

• The [ ] is a bash builtin for the test command.
• The && means that bash should execute the next command only if the previous completes successfully.
• The ( ) groups tests.
• The || is the OR list control operator.

That’ll work, & it’s shorter, but Robert took it even one step further:

#!/bin/bash

# Figure out how much RAM Java is using
# Uses the RSS column of ps (#6)
# RSS = the real memory (resident set) size of the process (in 1024 byte units)
javamem="$(ps aux | grep java | grep CrashPlan | awk -F' ' '{print $6}')"

# Get Java’s PID (2nd column of ps)
javapid="$(ps aux | grep java | grep CrashPlan | awk -F' ' '{print $2}')"

# Get current time
currenttime="$(date +%H%M)"

# If Java is using over 200 MB of RAM & it’s not between 1 & 9 a.m., kill it
[ $javamem -gt 204800 ] && ( [ $currenttime -lt 0100 ] || [ $currenttime -gt 0900 ] ) && kill $javapid

Robert, that last one is goooood. I like it! Short & sweet & clever. That one’s the ticket!