Its fun to try Strace on different commands to see what actually happens behind the command. There are some very good options to filter out required systems calls from the log.
The following link gives examples on how to use Strace http://www.thegeekstuff.com/2011/11/strace-examples/
one interesting system call is 'select' . I was only heard about 'select' in sql queries,but this is a different place i am seeing select :-)
"select() and pselect() allow a program to monitor multiple file descriptors, waiting until one or more of the file descriptors become "ready" for some class of I/O operation (e.g., input possible). A file descriptor is considered ready if it is possible to perform a corresponding I/O operation"
The sigaction() system call is used to change the action taken by a process on receipt of a specific signal.
I was watching the video on 'Type Python ,Press enter. What happens'. I thought of checking whether 'strace' can get the fork() system call that he explained in the video.
Unfortunately I couldn't get ....
But i came to know about the write and read system calls when we type the arithmetic operatons on python ... strace log pasted below.
Still I dont know where the calculation is happening.... is there any tool to list which part is calculating it ? where is the fork() ??
brk(0x19ed000) = 0x19ed000
ioctl(0, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or TCGETS, {B38400 opost isig icanon echo ...}) = 0
ioctl(1, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or TCGETS, {B38400 opost isig icanon echo ...}) = 0
write(2, ">>> ", 4) = 4
read(0, "1+2\n", 1024) = 4
fstat(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 6), ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f0206e7b000
write(1, "3\n", 2) = 2
ioctl(0, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or TCGETS, {B38400 opost isig icanon echo ...}) = 0
ioctl(1, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or TCGETS, {B38400 opost isig icanon echo ...}) = 0
write(2, ">>> ", 4) = 4
read(0, "1+4\n", 1024) = 4
write(1, "5\n", 2) = 2
ioctl(0, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or TCGETS, {B38400 opost isig icanon echo ...}) = 0
ioctl(1, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or TCGETS, {B38400 opost isig icanon echo ...}) = 0
write(2, ">>> ", 4) = 4
read(0,
I am started hearing about RUST programming language http://doc.rust-lang.org/book/README.html, so thought of give a try 'helloworld' program.
The impressive thing is,the language focus on safety,speed and concurrency.
Rust is a systems programming language focused on three goals: safety, speed, and concurrency. It maintains these goals without having a garbage collector, making it a useful language for a number of use cases other languages aren’t good at: embedding in other languages, programs with specific space and time requirements, and writing low-level code, like device drivers and operating systems
Below is the installation steps, helloworld program . I gave a 'Strace' on the program to see any difference.I couldn't understand any difference :-).. i dont know how to find the difference in speed or concurrency.. need to read more ...
Sometimes I think that I studied lot of things in engineering text books, but don't have any clue on how the concepts/formula derived or how much analysis they put behind on those concepts.That research or hacking experience generally missing in text books. Sorry ..I am not saying school/college text books are bad. We ( as students) always needs to read text books .. but what I am trying to convey is... sometimes textbooks are missing practical possibilities of formulas or concepts.
There comes the importance of unconventional way of studying things.. or the hackers(in good sense) way of mastering the interested areas. Our schools and colleges should give these kind of opportunities for students.
Okay.....
These things came to my mind when I was watching the below video...
I tried 'strace' against our normal linux command 'ls'. This actually listed me amazing tracing log ...
This is just an example .All concepts that we are studying/hearing should have unconventional way of mastering it or we should at least try to develop it !!!
None of the computer text books might have taught you on, what actually happens behind the 'ls' command. But the unconventional way is, find out some tool which can list the activities behind 'ls' and mastering what is it doing.... obviously it is very difficult, but it gives you the full concepts behind the 'ls' upto very low/machine level.
Unconventional way of studying things opens opportunities which are not described in most of the text books That gives you the confidence to question the actual concepts or current implementation.
But it will have some initial difficulties and extra research out of your text books or tutorials. But I am sure that there will be always some supporting tools/methods which somebody might have implemented already or you can implement such a method if it's not there!! :-)
Below is the screenshot of 'strace' on 'ls' in command line
some research on each system calls behind means ..
This is the best place to refer one who like to know about linux kernel. http://lxr.free-electrons.com/ LXR Cross Referencer, usually known as LXR, is a general-purpose source code indexer and cross-referencer that provides web-based browsing of source code, with links to the definition and usage of any identifier.
Wireshark is a network protocol analyzer. This is actually nice tool which gives opportunity to analyze and understand different network layers. Each packet traffic is diplayed when we start browsing a website.Its very easy to install in Ubuntu using 'Ubuntu Software center'. After installing I used the command and changed to root. I am not sure any alternative way for getting my 'wlan0' wifi internet without changing to root.
I am just writing this blog to make sure that I will refresh my system programming knowledge. Every time when I start motiviated with some concepts , it used to end in a week :-). Now I am going to try Networking modules in Linux kernel. As you all know , linux is like a ocean and any time we can go do some research and learn .. that what I like in GNU/Linux.
I got some tutorials from Youtube to start with the networking modules in Linux kernel.. don't know the opportunities that I am going to get in this. sharing some of the videos below .
