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Sunday, September 9, 2012

A different way of blogging, Linux Explore Group

 Linux Explore

Owner: Rahul Panwar
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Brief description: Linux is the future, Live your present and ready to welcome the future.
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10 Linux super-hacks for Linux Administrator

This article is a compilation of several interesting, unique command-line tricks that should help you squeeze more juice out of your system, improve your situational awareness of what goes on behind the curtains of the desktop, plus some rather unorthodox solutions that will melt the proverbial socks off your kernel.
Follow me for a round of creative administrative hacking.

1. Run top in batch mode

top is a handy utility for monitoring the utilization of your system. It is invoked from the command line and it works by displaying lots of useful information, including CPU and memory usage, the number of running processes, load, the top resource hitters, and other useful bits. By default, top refreshes its report every 3 seconds.
top
Most of us use top in this fashion; we run it inside the terminal, look on the statistics for a few seconds and then graciously quit and continue our work.
But what if you wanted to monitor the usage of your system resources unattended? In other words, let some system administration utility run and collect system information and write it to a log file every once in a while. Better yet, what if you wanted to run such a utility only for a given period of time, again without any user interaction?
There are many possible answers:
  • You could schedule a job via cron.
  • You could run a shell script that runs ps every X seconds or so in a loop, incrementing a counter until the desired number of interactions elapsed. But you would also need uptime to check the load and several other commands to monitor disk utilization and what not.
Instead of going wild about trying to patch a script, there’s a much, much simpler solution: top in batch mode.
top can be run non-interactively, in batch mode. Time delay and the number of iterations can be configured, giving you the ability to dictate the data collection as you see fit.
Here’s an example:
top -b -d 10 -n 3 >> top-file
We have top running in batch mode (-b). It’s going to refresh every 10 seconds, as specified by the delay (-d) flag, for a total count of 3 iterations (-n). The output will be sent to a file.
A few screenshots:
Batch mode 1
Batch mode 2
And that does the trick.
Speaking of writing to files …

2. Write to more than one file at once with tee

In general, with static data, this is not a problem. You simply repeat the write operation. With dynamic data, again, this is not that much of a problem. You capture the output into a temporary variable and then write it to a number of files.
But there’s an easier and faster way of doing it, without redirection and repetitive write operations. The answer: tee.
tee is a very useful utility that duplicates pipe content. Now, what makes tee really useful is that it can append data to existing files, making it ideal for writing periodic log information to multiple files at once.
Here’s a great example:
ps | tee file1 file2 file3
That’s it! We’re sending the output of the ps command to three different files! Or as many as we want. As you can see in the screenshots below, all three files were created at the same time and they all contain the same data. This is extremely useful for constantly changing output, which you must preserve in multiple instances without typing the same commands over and over like a keyboard-loving monkey.
tee 1
tee 2
tee 3
Now, if you wanted to append data to files, that is periodically update them, you would use the -a flag, like this:
ps | tee -a file1 file2 file3 file4
Sweet.

3. Unleash the accounting power with pacct

Did you know that you can log the completion of every single process running on your machine? You may even want to do this, for security, statistical purposes, load optimization, or any other administrative reason you may think of.
By default, process accounting (pacct) may not be activated on your machine. You might have to start it:
/usr/sbin/accton /var/account/pacct
Once this is done, every single process will be logged. You can find the logs under /var/account. The log itself is in binary form, so you will have to use a dumping utility to convert it to human-readable form.
To this end, you use the dump-acct utility.
dump-acct pacct
The output may be very long, depending on the activity on your machine and whether you rotate the logs, which you should, since the accounting logs can inflate very quickly.
dump-acct
And there you go, the list of all processes ran on our host since the moment we activated the accounting. The output is printed in nice columns and includes the following, from left to right: process name, user time, system time, effective time, UID, GID, memory, and date.
Other ways of starting accounting may be in the following forms:
/etc/init.d/psacct start
Or:
/etc/init.d/acct start
In fact, starting accounting using the init script is the preferred way of doing things. However, you should note that accounting is not a service in the typical form. The init script does not look for a running process – it merely checks for the lock file under /var. Therefore, if you turn the accounting on/off using the accton command, the init scripts won’t be aware of this and may report false results.
BTW, turning accounting off with accton is done just like that:
/usr/sbin/accton
When no file is specified, the accounting is turned off. When the command is run against a file, as we’ve demonstrated earlier, the accounting process is started. You should be careful when activating/deactivating the accounting and stick to one method of management, either via the accton command or using the init scripts.

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