How to check which process is causing IO wait

The ‘wa’ state in `top` can indicate an IO wait, but to figure out what’s causing the IO wait try this command:

# ps aux | awk '$8 ~ /D/  { print $0 }' | less

You can read more here. Thanks to bsandro on #lobsters.
According to `man top`:

The status of the task can be one of:
  D = uninterruptible sleep
  I = idle
  R = running
  S = sleeping
  T = stopped by job control signal
  t = stopped by debugger during trace
  Z = zombie

Bash wait

Today I learned about the ‘wait’ command. It waits for background processes to terminate before returning, so you can fire off a bunch of jobs to be run in parallel and then wait for all of them to complete before continuing, like in this script I wrote tonight:

if [ -n "$1" ]; then
  pushd "$1" > /dev/null 2>&1
  if [ "$?" -ne "0" ]; then
    echo "Cannot change dir to '$1'.";
    exit 1;
sudo chown -R jj5:jj5 . &
sudo find . -type d -exec chmod u+rwx {} \; &
sudo find . -type f -exec chmod u+rw {} \; &
if [ -n "$1" ]; then
  popd > /dev/null 2>&1
exit 0

Changing parent’s directory from a subshell

I was trying to figure out how to have a child process change the current directory of a parent process. Turns out you can’t quite do that. One thing I guess you could do is export a global variable and then have the parent check that when the child returns, but I decided on another approach. What I do is write a file to ~/bin/errdir that contains a single line in the format:

  pushd "/path/to/directory"

I can then source this as a command file after my script has run to change directory into the directory where the last erroneous file was encountered with the command:

  $ . errdir

When I’m finished I can just type ‘popd’ to return myself to wherever I was before I changed into the error directory.