strace - What Is It?

strace is an application that allows us to run another application, and see all (or a selected set of) the system call invocations this application performs.

We normally run it as:  strace /bin/mkdir /tmp/bla
and get output such as (full output trimmed).

execve("/bin/mkdir", ["/bin/mkdir", "/tmp/bla"], [/* 34 vars */]) = 0
uname({sys="Linux", node="simey", ...}) = 0
brk(0)                                  = 0x804c384
open("/etc/ld.so.preload", O_RDONLY)    = -1 ENOENT (No such file or directory)
open("/opt/xmps/lib/i586/mmx/libc.so.6", O_RDONLY) = -1 ENOENT (No such file or directory)
stat64("/opt/xmps/lib/i586/mmx", 0xbfffeb20) = -1 ENOENT (No such file or directory)
open("/opt/xmps/lib/i586/libc.so.6", O_RDONLY) = -1 ENOENT (No such file or directory)
stat64("/opt/xmps/lib/i586", 0xbfffeb20) = -1 ENOENT (No such file or directory)
open("/opt/xmps/lib/mmx/libc.so.6", O_RDONLY) = -1 ENOENT (No such file or directory)
stat64("/opt/xmps/lib/mmx", 0xbfffeb20) = -1 ENOENT (No such file or directory)
open("/opt/xmps/lib/libc.so.6", O_RDONLY) = -1 ENOENT (No such file or directory)
stat64("/opt/xmps/lib", {st_mode=S_IFDIR|0775, st_size=4096, ...}) = 0

(This is just small part of the output).