Tracing the execution of processes using strace

Strace is quite simply a tool that traces the execution of system calls. It can trace the execution of a binary from start to end, and output a line of text with the name of the system call, the arguments and the return value for every system call over the lifetime of the process.

   1.Find out which config files a program reads on startup

strace php 2>&1 | grep php.ini

open("/usr/local/bin/php.ini", O_RDONLY) = -1 ENOENT (No such file or directory)

open("/usr/local/lib/php.ini", O_RDONLY) = 4

lstat64("/usr/local/lib/php.ini", {st_mode=S_IFLNK|0777, st_size=27, ...}) = 0

readlink("/usr/local/lib/php.ini", "/usr/local/Zend/etc/php.ini", 4096) = 27

lstat64("/usr/local/Zend/etc/php.ini", {st_mode=S_IFREG|0664, st_size=40971, ...}) = 0

2.What is that process doing RIGHT NOW?

Ever had a process suddenly eating lots of CPU? Or had a process seem to be hanging? Then you find the pid, and do this:

root@dev:~# strace -p 15427

Process 15427 attached - interrupt to quit

futex(0x402f4900, FUTEX_WAIT, 2, NULL

Process 15427 detached

3.MySQL with strace

Start MySQL Daemon

service mysqld start

Connect strace to mysqld

ps -elf | grep mysqld (and find out that mysqld is PID 1234)

sudo strace -p 1234 -f