How it works

The at command is often used to start a process at a later time. It can run any script at a specified date and time.

For instance, if you want the computer to send you a signal in one hour, use something like:

cat signal | at -q z now + 60 minutes

Assuming that the file named signal contains the commands necessary to generate the signal. Then in 60 minutes, the script will be execute and the signal will be heard or shown.

Since my last upgrade, I had many small things that went awry on my computer. From tsearch2 in a Postgres database to ownership of files to the following authentication problem:

root@mycomputer:~# su - www-data
su: Authentication service cannot retrieve authentication info
(Ignored)
www-data@mycomputer:~$

Note that with su it ignores the fact. With cron it was not being ignored, so I'd get no work done!

Got to setup a new server and first got the firewall to where I wanted it to be:

• Block everything except ssh, Apache, SMTP, a few other things, but really not much more than that.
• Block everything with IPv6 since we don't use it.

Then I installed Apache and a couple of websites.

The first one finally started to work, but it was so very slow to show up. I checked the code, the database, nothing wrong... And the database is lightning fast! ( in comparison to our previous server that is.)

Today, I was trying to run psql from a program when I got this error:

  Insecure $ENV{PATH} while running setuid at ...

At first, I thought that psql would be testing something about the user, but in fact, psql is a perl script that runs in secure mode. In other words, this applies to any tool written in perl.

The perl interpreter makes sure that the current user identifier is the same as the effective user identifier. When there is a mismatch, the interpreter breaks with that error.