So you've installed spamassassin and it works good but you still are getting unflagged spam emails through? Perhaps you need to try greylisting.

When you're running production servers, the one thing you don't want to do is upgrade the kernel every time a new update comes out. Why? Because that's the only Linux update operation that requires a reboot once it's done—and in a production environment you often can't have downtime.

How to change the hostname quickly and without rebooting the box since there are 18,000 users all trying today to access data from that one server?

If you have been an admin for any length of time, you have certainly discovered situations where a server spikes in CPU use or memory utilization and/or load levels. Running `top` won't always give you the answer, either. So how do you find those sneaky processes that are chewing up your system resources to be able to kill 'em?

Have you ever needed to find all the PDF files on your drive, and organize them into one place?

Ever needed to make a quick adjustment to the php.ini file but you weren't sure where it was? Here's a quick command you can use.

Have you ever been on a system that has a whole bunch of aliases, like changing rm to rm -i, and you want it to work the way you're used to?  There's an easy way to do it.

Ever forgotten to run the last command with sudo at the beginning? Here's how to re-run the command with sudo at the beginning, without re-typing the whole thing:

You might want to reuse all of the arguments to a previous command in the shell if you realized you want to open the file with a different utility, but don't feel like typing out the whole path again.

Have you ever typed out a really long command, realized it worked great, and then wanted to save it to a file? There's an easy bash trick you can use to do just that.

If you're working on a project, and you've copied in or created a whole bunch of new files, you might find it tedious to manually add each of them. Here's the quick command you can use instead.

If you want to quickly see what processes are wasting all of your memory, you can do so with a simple command.

If you've got a web application that uploads files to the server through a PHP script, you might have noticed that by default you can't upload terribly large files. Here's how to change it.

Have you ever used a tail -f on a logfile, only to find that it's scrolling by way too fast for you to deal with?

Changing the group a user is associated to is a fairly easy task, but not everybody knows the commands, especially to add a user to a secondary group.

Have you ever needed to quickly share a folder with another machine?

If you use the rsync utility to keep your backups synchronized from your database server over to your backup or secondary file server, you might want to prevent the script from using too much bandwidth. Here's how.

If you are new to the world of Linux, you probably unzip your tar.gz files first, and then extract them from the tar file… at least, if you are even bothering to use the command prompt at all. It’s easy to gunzip or even bunzip2 the files with a simple command-line switch. To gunzip and untar [...]

Creating a new user on Ubuntu server is easy—just sudo your shell to root, or run the following command: adduser username This will create the user, with output something like this: root@ubuntugeek910:~# adduser testuserAdding user `testuser' ...Adding new group `testuser' (1001) ...Adding new user `testuser' (1001) with group `testuser' ...Creating home directory `/home/testuser' ...Copying files from `/etc/skel' ... You [...]