top -b -n 1 -u jimgreen | awk 'NR>7 { sum += $9; } END { print sum; }'

You can even further capture the usage metric in PHP and do conditional actions:
$usage = shell_exec("top -b -n 1 -u jimgreen | awk 'NR>7 { sum += $9; } END { print sum; }'");
Now $usage contains the CPU usage of the user jimgreen.

wc -l file.txt

You know how to list the content (files and directories) of a tar archive?

tar --list example.tar

Now you just combine these two to count the number of lines of the files list of the tar archive:

tar --list example.tar | wc -l

So that you have the number of files in the tar file example.tar. The pipe means relaying the output of the previous command to the next command as input.

wc -l /etc/passwd

And it may output something like this:

76 /etc/passwd

Which means there are a total of 76 active users in the system. However, the actual number of human users of the server should be lower than the amount because there are system users created to carry out certain tasks.

Multiply the amount by 5 and you may get a rough number of websites hosted on your server.

wget http://www.google.com/money.zip

However, there’s yet another hidden trick of wget that could enable you to make a mirror backup of any website – well, not actually any website but wget feels more comfortable with certain sites. WordPress blogs are perfect candidates for wget to mirror. Mirroring a WordPress blog can be done by a very simple switch of the wget command through SSH:

wget -mk http://www.example.com

All the documents relationships and HTML links will be taken care of so that local browsing of the mirrored copy will be completely no problem.

The location of php.ini varies distribution by distribution, in this example, with Ubuntu 9.04 Jaunty, php.ini is located at /etc/php5/apache2/php.ini, so

sudo vi /etc/php5/apache2/php.ini

Press / to find upload_max_filesize and change it to, say 8M:

upload_max_filesize = 8M

Press ESC, :, wq and Enter. Now the php.ini is saved with the new uploading file limit. Reload apache2 to read the new configurations:

sudo /etc/init.d/apache2 reload

Now you should be able to upload any file up to 8MB in size, in case you need larger uploading limit, in addition to change upload_max_filesize to, say, 16M, you must also edit post_max_size to more than or equaling to 16M because file uploads are processed through HTTP POST method.

Web Developers / Designers’ Books:

1. Best HTML Books
2. Best CSS Books
3. Best JavaScript Books
4. Best PHP Books
5. Best MySQL Books
6. Best Linux Books
7. Best Apache Books (mod_rewrite Books)
8. Best Web Hosting Books

The Definitive Guide to Apache mod_rewrite

Oh wait, I think I forget about how to get the IP address of a website. All after all, you can ping the domain name to get the IP address of the site from command line. Or, you can use domain IP lookup tools such as this one. It not only gives you the IP address of the particular domain URL but also pokes the server around and guesses what other sites are possibly being hosted on that IP.

Actually, there’s a much simpler one to consult when you need to know the physical location of a site and where the website is hosted: Domain Tools. By querying a domain, it gives you the IP where the domain / site is currently hosted and also the organization or data center (might be a hosting company) that’s administering the IP. Very good tool to know where a site or domain is hosted.

After installing rsync on all peer hosting servers you own, you can easily backup stuff and synchronize them among the servers for a safe data redundancy.

rsync -e 'ssh -p 25000' -avl --delete --stats --progress user1@123.45.67.890:/home/user1 /backup

This simple command will take care of everything for you, the rsync command connects to the remote server 123.45.67.890 as user1 and backups or synchronizes everything in /home/user1 from the remote server to the local directory /backup. The –delete switch indicates that files that previously existed at /home/user1 on the remote server but not now will be also deleted in /backup at the local server.

‘ssh -p 25000′ prescribes rsync to connect via SSH on port 25000.

Find and edit /etc/vim/vimrc with vi:

vi /etc/vim/vimrc

And add in this line:

colorscheme desert

Wherein desert is one of the available color schemes vim comes with. Now we will need to edit the actual color scheme file and change the highlighting colors:

/usr/share/vim/vimcurrent/colors/desert.vim

Change:

hi Comment ctermfg=darkcyan

To:

hi Comment ctermfg=blue

Save the change and exit. Run:

source /etc/vim/vimrc

And the changes will now take effect.

The default directory color of ls –color is also too dark, you can learn how to change the default directory color of ls –color.

Just open up the .profile or .bash_profile file under your home directory and put this line in it:

export LS_COLORS='di=01;34'

Done! Now the color of the ls directory listings is much lighter and easier to recognize. There’s also a tip of how to change the default dark color for comments in vi text editor.

export PS1='[\[\e[1;31m\]\u\[\e[0m\] - \[\e[32m\]\w\[\e[0m\]]$ '
export LS_COLORS='di=01;34'
alias ls='ls --color -l'

If you are ‘supergirl’, your Linux home directory would be located at: /home/supergirl, and the file you should add the above lines to is: /home/supergirl/.profile or /home/supergirl/.bash_profile.

What is LS_COLORS doing here?

To show used and available RAM memory and swap space usage:

free -m

To show current disk storage usage by mounted device:

df

To show disk usage statistics of the current directory by directories and files:

du

To show the hard disk space a directory or a file takes up:

du filename

To show the length of time this server has been up and the server loads in the past 1 minute, 5 minutes and 15 minutes:

uptime

To display a real-time updated server resource usage including: server uptime, user logged on, load average, current tasks, CPU usage, memory usage and swap usage:

top

To display a list of real-time active or sleeping processes your server is up to:

ps

To show some information about the current status of virtual memory, CPU usage, I/O usage:

vmstat

This is also a good tool to find out system performance bottlenecks.

To display currently logged on users on the system:

w

Or

who

To print a full screen text graph of the server load refreshed every few seconds:

tload

If you are on shared hosting, chances are your server usage has been imposed some hard limits such as the largest amount of files / directories possible and the hard storage limit. View them by:

quota

As a result of the nature of VPS, an entire operating system (such as Linux distributions: Ubuntu, Debian or Centos, and so forth) resides in it with a complete web server package: Apache, PHP, MySQL and potentially a lot of necessary modules and extensions, making the mere hosting slice of 256MB a frugal choice to cover all the overheads, much like the sunk cost in Economics. It is after the threshold of 256MB that every additional MB of RAM you purchase will be consumed by your own websites rather than by the system. Well, not precisely all of 256MB will be used for the system, but you are left with like 50MB – 100MB from the whole 256MB pie after installing everything WWW and getting your slice ready for websites.

So if you are going to switch to a VPS, make sure you board on at least 512MB memeory for a start or it won’t be worth the while and it may just be good enough to spread your sites across various shared hosting plans (preferrably from various distant hosting comapnies) for some SEO advantage.

1. Check for the number of server processors or CPUs
2. Check for the average load the server is experiencing

Get the 3 load average figures divided by the number of CPU they have on the server, add them up and further divide them by 3. With the final result:

• result <= 1 ( definitely an honest and great host)
• 1 < result <= 2 (good one, but questionable)
• 2 < result <= 5 (overselling, overselling, overselling, …)
• result > 5 (are you crazy?!)

uptime

Which will typically return a line of data similar to this:

21:39:33 up 10:45, 3 users, load average: 4.46, 3.92, 3.64

That says there are currently 3 users logged on and the load average of this server in the last minute, last 5 minutes and last 15 minutes are 4.46, 3.92 and 3.64. These figures represent the number of runnable processes at the same time on average for the CPUs (processor) to process. Combined with number of processors of the server, you may know how many processes are being processed by any single CPU.

Considering the fact that any CPU can only take on one process at any given time, there will possibly be processes waiting in the queue – meaning server is overloaded. Therefore, if the number of processors of your hosting server is 4, in the last minute, it is overloaded by ( 4.46 / 4 ) – 100% = 11.5%.