You may also find this article of interest: Setting Up a Full Powered SAMBA Server

A brief version of these commands also ran in my article for Linux+ Magazine (lpmagazine.com).

Sitting in the freezing cold server room one evening, I shared some tips with my colleague who was still learning server administration.

at

This often ignored tool covers when you need a very quick solution rather than modifying your cron tab. With this too you can quickly run any command or process at a later time using a very easy to understand syntax. For example, running as root type:

at midnight

Once you press enter you will see the at prompt. Beside the at> type a specific command. For example, to run a command at midnight tonight, start by typing: 

at> who > who.out

Pressing enter again will ensure that this command will run at the specified time frame (eg. midnight, noon, teatime, etc). Press the Ctrl and D keys simultaneously to exit the at prompt.

You should now see:

X  2006-05-26 00:00 a name

The X represents the number assigned to your new at command. This indicates that an automated process will run your specified command tonight at midnight (00:00).

If you decide, prior to midnight, not to run this command, then type:

atrm X

Ensure you replace the X with the number of your command. The syntax allows you to many easy to remember time increments, such as midnight, teatime, morning, noon, etc.

chkconfig

This is a very important administrative command and I suggest you get well familiar with it. I have many details about this command as well as other server commands on my Linux Server Admin commands page. The chkconfig command allows you to determine whether core processes and daemons are active. I suggest using the following syntax::

/sbin/chkconfig -list

This command provides a long list of processes with details of their status. Any process with the word "off" next to it is disabled. Troubleshooting issues with your server should begin with this command, which clearly denotes if a daemon or process is running or off.

du

The display usage command allows you to identify the size of files in specific directories. However, please do NOT run this command from the / directory. It will display size for every file on the entire hard disk within a specific directory.

I suggest you run this command from a specific sub-directory by first changing directory, then using the syntax: du -a

df

The df command provides a quick check of your file system disk space.
Type df -h -T to get a simplified output that includes your file system type information. Notice that this command details all storage devices such as your hard disk/s (hda, hdb etc.) and your server SWAP file (shm).

find

Find command allows you to locate files quickly across an entire file system The most common syntax is:

find / -name filename -type d -xdev
Please replace the word filename with the name of a specific file.

The example shown allows you to search against all directories below / for the filename found in directories, but only on the existing file system

free

A nice name for a quick command to check system memory. It is useful when trying to determine the status of your SWAP file during certain load instances. From the command line type:

free -l

I tend to run this command with the -l option as it helps determine where my low memory and high memory stats are during peak loads or testing. Regardless how you use it, you'll find this a handy command for basic memory statistics and performance analysis.

grep

The grep command searches text files for a particular word or string of words. I have many details about this command as well as other server commands on my Linux Server Admin commands page. The grep command can be very helpful when trying to find that needle in a haystack, like a particular line in a large log file. Use the syntax: grep textstring filename

lsof

This command is short for "list open files." In the man pages it is properly documented as a method for listing any form of open file, including for example "a network file." But notice that what this actually means it that you are able to list open sockets, and even run in repeat mode allowing for time intervals between each pass. All that to say this is a very powerful and useful command for admins. From the command line you simply type: lsof

However, I tend to use this command to check open ports, and to do so you simply type the command with the -i option followed by a specific port number: lsof -i :443

netstat

The netstat command provides a summary status of all network connections and sockets.

I find the most helpful syntax is either: netstat |head or to use netstat -r

Using the -r option gives you a very good look at the network routing addresses. This is directly linked to the route command.

top

You may already be familiar with the top command. It is especially helpful since it displays system statistics and details regarding active processes. Using this command gives you a summary view of the system with a listing of users, memory usage, CPU usage, and associated processes.

uptime

The uptime command checks for your server's total uptime statistics. Running this simple command is especially useful for performance checking, since it will also display the average system load over the past few minutes.

Mark Rais has written numerous articles on integrating Linux and Windows including his featured article Moving to Linux for Business. Besides serving as managing editor for reallylinux.com Rais also contributes as a technology consultant for educational and non-profit organizations.

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