system calls tracing

Because the logs are not explicit or not reachable, it is sometimes necessary to trace the system calls used by an application.
This can help to find the cause of an error or a crash.

GNU/Linux

On GNU/Linux, there is strace:

root$ strace -s 2000 -f /path/of/app 2>&1
root$ strace -s 2000 -fp the_pid 2>&1
The option:
-f display also all children syscalls
-s allow to display more characters of the lines returned by strace (useful for long message like paths)
-p allow to trace the calls of an already running process

OpenBSD

On OpenBSD, there is ktrace: todo