Sometimes, a program starts behaving errantly. It gives incorrect output on its input, it doesn't print anything at all, or even hangs. Under a Linux-based system, every userspace process has to interact with its environment through the kernel. And it does this by invoking system calls.

Strace is a utility that intercepts and logs these system calls. In this way, you can watch how a program interacts with the system, which is useful for tracking down behavioural issues.

Generation

1. Make sure strace is installed.

   apt-get install strace

2. Start the program under control of strace:

   strace -Ff -tt <program> <arguments> 2>&1 | tee strace-<program>.log

3. The program will start. Perform any actions necessary to reproduce the crash

4. Attach the complete output from strace, contained in strace-<program>.log, in your bug report.

Already running programs

You may want to run strace on an already running program. This could be because strace logs too many things before you can reproduce a crash. Or, it could be because you are trying to find out what a program is doing in an infinite loop.

1. Make sure strace is installed.

   apt-get install strace

2. Find the process ID of <program>:

   pidof <program>

3. Start strace with the process ID:

   strace -Ff -tt -p <PID> 2>&1 | tee strace-<program>.log

4. Perform any actions necessary to reproduce the bug.
5. You may have to hit Control-C to get strace to detach from a running program.

6. Attach the complete output from strace, contained in strace-<program>.log, in your bug report.

Already running programs - using htop

This is an easy way to run strace on a running program. You will, however, not be able to store the output of the strace in a logfile.

1. Make sure strace and htop is installed.

   apt-get install strace htop

2. Start htop.

   htop

3. Use arrow keys to choose desired process, then press "s" to display a strace of the process on-screen.