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Sendmail does not provide a command-line argument to remove messages from the mail queue. It may be necessary to manually remove messages from the mail queue rather than allowing Sendmail to attempt redelivery of messages for Timeout.queureturn days (5, by default).

The proper way to remove messages from the mail queue is to use the qtool.pl program included in the contrib subdirectory of the Sendmail source code distribution. qtool.pl uses the same file locking mechanism as Sendmail...

Adjusting sendmail queue time / lifetime

By default, sendmail will keep items in the queue for up to 5 days. If you want to make this something shorter, like 3 days, you can adjust the following in /etc/mail/sendmail.mc:

So you think your OpenVZ VPS really has “guaranteed memory”? Well. Not quite. I have got an OpenVZ VPS from one of the providers listed here — 256MB guaranteed and 512MB burstable memory. When I run free it shows... 512MB total memory and 0 swap? After all I am only using 65MB of memory so well below my “guaranteed” amount. Zero swap because it is just how OpenVZ does its memory account. But is it really the case that all my processes reside in physical RAM?

Let’s dig out the good ol’ user_beancounters...

Experimenting with Varnish...
Using the varnish HTTP accelerator - Experiences so far...

The best way to think of things is that as a request comes in, Nginx will scan through the configuration to find a “location” line that matches the request. There are TWO modes that nginx uses to scan through the configuration file: literal string matching and regular expression checks. Nginx first scans through ALL literal string location entries in the order that they occur in the configuration file, and secondly scans through ALL the regular expression location entries in the order that they occur in the configuration file. So be aware – location ordering order DOES matter...

Nginx is a fast and efficient web server. It can be configured to serve out files or be a reverse proxy depending on your application. What makes this web server different from Apache, Lighttpd or thttpd is the overall efficiency of the daemon, the number of configuration options and how easy it is to setup....

One of the most commonly seen questions when dealing with firewalls and other Internet connectivity issues is the difference between active and passive FTP and how best to support either or both of them. Hopefully the following text will help to clear up some of the confusion over how to support FTP in a firewalled environment...

The output of SQL Plus can be a annoying a little bit. Here are some techniques that show how to enhance the readability of SQL Plus output...

How do I audit file events such as read / write etc? How can I use audit to see who changed a file in Linux?

The answer is to use 2.6 kernel’s audit system. Modern Linux kernel (2.6.x) comes with auditd daemon. It’s responsible for writing audit records to the disk. During startup, the rules in /etc/audit.rules are read by this daemon. You can open /etc/audit.rules file and make changes such as setup audit file log location and other option. The default file is good enough to get started with auditd.

To write a message to users that have login, you can using the command write. But before that, you need to check who is login, and which terminal he is login to, use command who...