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LCSA Exam Tips

If you're going for the Linux on Azure certification, you'll be taking the LCSA exam. This is a practicum, so you're going to be going through a series of requirements that you'll have to implement.

Ignore the naive folk who say that this is a real exam, "unlike those that simply require to you memorize a bunch of stuff". The problem today is NOT with people having too much book knowledge, but nowhere near enough. Good for you for going for a practicum exam. Now study for the cross-distro LPIC exams so you don't get tunnel vision in your own little world. Those exams will expand your horizons into areas you may not have known about. Remember: it's easy to fool yourself into thinking that you have skill when you do the same thing every day. Perhaps your LCSA exam will simply match your day job and you'll think you're simply hardcore. Go study the books and get your humility with the written exams. You know, the ones where you can't simply type man every time you have a problem.

Here are some tips:

noclobber

In whatever account (e.g. some user or root) you'll be using, set the following:

set -o noclobber

This will make it so that if you accidentally use > instead of >>, you won't automatically fail. It will simply prevent overwriting some critical file.

For example, if you're trying to send a new line to /etc/fstab, you may want to do the following:

echo `blkid | grep sdb1`    /mng/taco    xfs    defaults    0 0 >> /etc/fstab

Yeah, you'll need to edit the UUID format after that, but regardless: the >> means append. If you accidentally use >, you're dead. You've already failed the exam. The system needs to boot. No fstab => no boot.

/root/notes

The requirements you'll be given will, like with all requirements, they require careful thought and interpretation. Your thought process at may be more clear later. This is why giving estimates on the job RIGHT THEN AND THERE is what we technically call "full retard". In this exam, you've got 2 hours. It's best not to sit there and dwell. Go onto other things and come back.

In this process, you'll want to store your mental process, but you can't write anything down and there's also no in-exam notepad. So, I like to throw notes in some random file.

echo review ulimits again >> /root/notes

Again, if you accidentally used > instead of >>, you'd overwrite your notes.

The forward/backward buttons in the exams are truly horrible. It's like trying to find a scene in a VHS. There's no seek, you have to scroll all the way through the questions to get back to what you want to see. Just write the question in your notes.

Using command comments

If you're in the middle of a command and you realize "uhhh.... I have no idea how to do this next part", you may want to hit the manpages.

BUT! What about the line you're currently on? Just throw # in front of it and hit enter. It will go into your history so you can pick it up later to finish.

Example:

$ #chmod 02660 /etc/s

You can't remember the rest of the path, do you have to look it up. CTRL-A to the begining of the line and put #. Hitting enter will put it into history without an error.

Consider using sed

Your initial thought may be "hmm vi!" That's usually a good bet for any question, but you better know sed. With sed you can do something like this:

sed "/^#/d" /etc/frank/data.txt 

This will delete all lines that start with #, but it will only send the output to YOU, it won't actually update the file.

If you like what you see, do this:

sed -i.original "/^#/d" /etc/frank/data.txt

This will update the file, but save the original to data.txt.original

Remember the absolute basics of awk

Always remember at least the following, this single command accounts for the 80/20 of all my awk usage:

awk '{print $2}'

Example:

ls -l /etc/hosts* | awk '{ print $9 }'

Output:

/etc/hosts
/etc/hosts.allow
/etc/hosts.deny

Probably the worst example in the world, but the point is: you get the 9th column of the output. Pipe that to whatever and move on.

Need two columns?

ls -l /etc/hosts* | awk '{ print $5, $9 }'

Output:

338 /etc/hosts
370 /etc/hosts.allow
460 /etc/hosts.den

Know vi

If you don't know vi, you aren't going to even take the LFCS exam. It's a moot point. The shortcuts, text editing capabilities, and absolute ubiquity of vi makes it something you do not have the option to ignore.

Know find

Believe me, the following command pattern will save you in the exam and on the job:

find . -name "*.txt" -exec cp {} /tmp\;

The stuff after -exec runs once per file found. Instead of doing stuff one-at-a-time, you can use find to process a bunch of stuff at once. The {} represents the file. So, this is copy each file found to /tmp.

Know head / tail (and all the other standard tools!)

If you're like me, when you're in a test, you could read "How many moons does Earth have?" and you'll quickly doubt yourself. Aside from the fact that Steven Fry on QI sometimes says Earth has two moons, and other times says Earth has none, the point is that it's easy to forget everything you think is obvious.

So, if you need to do something with certain files in a list and can't remember for the life of you how you to deal with files 90-130, perhaps you do this:

ls -l | head -n130 | tail -n40

Then do some type of awk to get the file name and do whatever.

That's one thing that's easy about this exam: you can forget your own name and still stumble through it since only the end result is graded.

Know for

I love for. I use this constantly. For example:

for n in `seq 10`; do touch $n; done

That just made 10 files.

Need to create 10 5MB files?

for n in `seq 10`; do dd if=/dev/zero of=/tmp/$n.img bs=1M count=5; done

I love using that to test synchronization.

Know how to login as other users

If you're asked to do something with rights, you'll probably want to jump over to that user to test what you've done.

su - dbetz

As root, that will get me into the dbetz account. Once in there I can make sure the rights I supposedly assigned are applied properly.

Not only that, but if I'm playing with sudo, I can go from root to dbetz then try to sudo from there.

Know how to figure stuff out

Obviously, there's the man pages. I'm convinced these exist primarily so random complete jerks on the Internet can tell you to read the manual. They are often a great reference, but they are just that: a reference. Nobody sits down and reads them like a novel. Often, they are so cryptic, that you're stuck.

So, have alternate ways of figuring stuff out. For example, you might want to know where other docs are:

find / -name "*share*" | grep docs

That's a wildly hacky way to find some docs, but that's the point. Just start throwing searches out there.

You'll also want to remember the mere existence of various files. For example, /etc/bashrc and /etc/profile. Which calls which? Just open them and look. This isn't a written test where you have to actually know this stuff. The system itself makes it an open book exam. For the LPIC exams, you need to know this upfront.

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