The problem

In last week's post, I discussed using cpulimit on multiple processes in the special case of web browsers, but I wanted a more general solution.

The solution

cpulimit-all.sh is a wrapper around cpulimit which will call cpulimit many times to cover multiple processes of the same name and subprocesses.

Using that script, the follow is the equivalent of the script from last week to limit all browser processes to 10% CPU:

cpulimit-all.sh --limit=10 --max-depth=1 \
    -e firefox -e firefox-esr -e chromium -e chrome

But also, we can add a couple options to include any grandchild processes and check for new processes to limit every minute:

cpulimit-all.sh --limit=10 --max-depth=2 \
    -e firefox -e firefox-esr -e chromium -e chrome \
    --watch-interval=1m

The details

The problem

cpulimit is a useful utility for stopping a program from wasting CPU, but it only limits a single process. As all modern web browsers use process isolation, limiting just a single process doesn't do very much, we actually want to limit all of the browser processes.

The solution

The following script will limit the CPU usage of all browser processes to $LIMIT percent CPU. Note that the limit is per process not total over all processes, so you may want to set it quite low to actually have an effect.

LIMIT=10 # Hard-code a limit of 10% CPU as an example.

# Kill child processes (stop limiting CPU) on script exit.
for sig in INT QUIT HUP TERM; do
  trap "
    pkill -P $$
    trap - $sig EXIT
    kill -s $sig "'"$$"' "$sig"
done
trap cleanup EXIT

# Find and limit all child processes of all browsers.
for name in firefox firefox-esr chromium chrome
do
    for ppid in $(pgrep "$name")
    do
        cpulimit --pid="$ppid" --limit="$LIMIT" &
        for pid in "$ppid" $(pgrep --parent "$ppid")
        do
            cpulimit --pid="$pid" --limit="$LIMIT" &
        done
    done
done

The details

The problem

$ ls > file

doesn't do what you expect:

$ touch foo
$ touch bar
$ ls > filelist
$ cat filelist
bar
filelist
foo

You probably didn't expect, or want, filelist to be listed in filelist.

The solution

$ filelist=$(ls); echo "$filelist" >filelist