tools.md

Debugging

Language-agnostic ways to figure out what your code is doing

System tools

Let's analyze some running processes

Overall system

• dstat -nvl 5
  • vmstat 5
  • iostat 5
• nproc
• lscpu

Individual processes

• ps fuxS
• htop -u $USER
  • top -u $USER
• w -f

Open files per process

• lsof -p $PID
  • ls -l /proc/$PID/fd
• cat /proc/$PID/fdinfo/$FD

Process activity

• strace -p $PID

Other useful tools

• watch 'COMMAND ...'

Print statements

• Be careful of buffering
• Make sure to flush! (fflush(stdout), print(..., flush=True))
• python -u (PYTHONUNBUFFERED=1)

Core dumps

• ulimit -c unlimited
• ls /tmp/core.*