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(upbeat music)

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- [Instructor] Let's do a couple challenges related

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to system calls to get a little better idea

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about their usage.

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So we want to use the strace command again, right?

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That's all about system calls.

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So use the man page for strace

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and search for it for a summary option that shows a count

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of the number of times each system call

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was called by a process.

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And then try that out when you run the date command

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to find out which system call was called the most number

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of times when you ran date.

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Second challenge, and this one's a little tricky,

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is using strace,

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can you figure out which system call is used

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to change directory?

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And then the last one, this one's also a little bit tricky.

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Create a one line shell script

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that just does date space greater than /def/null.

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Then use strace with the minus F option,

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which will follow processes as they get started.

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And the minus O option

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where you give a file name which gets created

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and the trace goes into that file,

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and then use that to follow the new processes

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and all the output and so forth.

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When you run your script with the bash command

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to run date and redirect the output to /def/null.

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The idea is we want to find out

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is it the date process that opens /def/null,

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or is it the Bash process that opens /def/null

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before the Bash process starts up the date command?

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Good luck.