Simon Krenger

When using a server with multiple external users, one thing that regularly comes up is that users want to access a folder on the server, such as the root folder for a webserver. This way every user can manage their files and upload new content. This can be achieved securely with SFTP, which uses the SSH protocol for file transfers.

In this article, I provide a simple script to create new users with minimal preparation and all correct settings. The text is based on the following article on debian-administration.org: OpenSSH SFTP chroot() with ChrootDirectory.

Since I started out with Linux (so about six years ago), I always used the Linux Logical Volume Manager (LVM) to partition my tables. First it was just because it seemed easier to configure my harddisks with it (also, the installer usually provided a nice option to do so), but in the last few months I had the possibility to work more with LVM and got to know some nice features.

One thing I regularly have to do is to extend an existing logical volume on a server. This article focuses on extending a logical volume with the help of LVM.

On one of our Debian hosts, we use bash scripts and cron jobs to automate certain tasks. One of these bash scripts downloads files from an FTP server and archives them. After upgrading the host machine to Debian 6.0.4, one of the bash scripts suddenly showed warnings:

/srv/foo/bar.sh: line 146: warning: here-document at line 140 delimited by end-of-file (wanted `EOF')

Whoops, so let’s look into it. The change was probably introduced with the new version of bash:

Since most of our databases are not licensed with the Oracle Enterprise Manager Diagnostic Pack, we cannot use AWR (Automatic Workload Repository) and ADDM (Automatic Database Diagnostic Monitor). So we have to use the good old Oracle STATSPACK.

The goal of this article is to provide a quick reference for installing and maintaining STATSPACK for an Oracle database. It is based on the excellent “STATSPACK Survival Guide” of Akadia AG. If you need more information on STATSPACK, please refer to the Survival Guide or the Oracle documentation, since this article is only a really quick summary on how to install, configure and use STATSPACK.

Due to a a request, I am uploading a more current version of the Tanuki Service Wrapper for Windows x64 (Community edition). I used these instructions to build the wrapper. Find the download link below.

As always, I don’t guarantee anything, so please note:

For our courses in linear algebra, we are using the GNU Octave software for numerical computation. Since I am using a MacBook Air for university, I had to install Octave on Mac OS X. I simply followed the steps described here and successfully installed gnuplot and the Octave software package. But when I tried to plot something with Octave, I received the following error message:

When setting up a new server in a highly secured network, one does not always have access to the Red Hat Network to download packages for the installation of the server. Often, a local repository is provided later on in the setup process.

This leaves us with the problem of installing the necessary packages for the Oracle database. Luckily, we can use the DVD we used for the installation of the Operating System to get all required packages.

On a few test databases, test managers often need to preserve certain states in the database. This is why we use daily datapump scripts to create exports for archival.

It is important to note that such scripts are never a replacement for a proper RMAN backup, but an easy way to preserve multiple states of a database and reuse data where applicable.

This batch file uses the expdp tool provided by Oracle and the 7-zip archiver to compress the exports for archival. The export tool itself creates a full export of the whole database (full=y). Also, the flashback_time parameter is specified to get a consistent export.

Ok, here is a quick trick that I just found out about earlier this week. I am currently in an Oracle Database 11g: Administration 11 course and learn many new things about database administration.

One thing you will definitely encounter when working with Linux is that it is not possible to scroll back though your SQL*Plus history with the arrow keys. If you try to do so, the following happens:

SQL> select owner, count(1) from dba_tables group by owner;

OWNER				 COUNT(1)
------------------------------ ----------
[..]
SYS				      673
SIMON				       88


7 rows selected.

SQL> ^[[A     " - rest of line ignored.
SQL> command "
SQL> 

Argh! Some kind of wild character sequence appears on the command line. A quick search shows that this is a common problem. One thing that regularly happens is that you enter a SELECT statement that returns too many rows. Because the terminal buffer only contains a certain number of rows, your query disappears and you have to retype it.

Some services (such as MSSQL instances) include a dollar character ($) in their name. A few weeks ago, I had to add a service called “$02_JBoss Server” to our internal Nagios configuration. After searching through the Nagios documentation and FAQs, this is what I found:

For Nagios 3, add two backslashes and a second dollar (\$) symbol, like this: check_command check_command check_nt!SERVICESTATE!-d SHOWALL -l MSSQL\$$INSTANCE

The above example actually has a small error in it, because there is no second backslash (even though it says so in the description)!

The correct way to check a service named “$02_JBoss Server” is to use a definition like this:

check_command           check_nrpe_args!CheckServiceState!ShowAll "\\$02_JBoss Server"