OpenSSH SOCKS proxy support

by admin

Often, when you’re administering or developing on servers remotely, you may need to access resources that are not available to the public. There are several different ways that you can gain access to protected services from a remote location, including a VPN, port forwarding over SSH, and stunnel.

However, one method that is not as well known is OpenSSH’s SOCKS proxy option. Introduced in OpenSSH 3.7, SOCKS support allows you to easily tunnel traffic from any application that has support for a SOCKS4 or SOCKS5 proxy through your SSH connection. To do this, you simply need to add ‘-D <port>’ to your ssh connection string, where <port> is the port you would like your proxy to run on. Then, configure your application to use a proxy at localhost:<port>, and all of the traffic from that application will be tunneled through your SSH connection.

In addition to accessing protected resources, you can also use this for more everyday tasks – such as encrypting traffic sent over a public wireless connection.

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Mysql table opens, caching and iowait times

by Michael Klatsky

One issue that seems to be very common when running a MySQL server is high iowait. As we have delved into our servers, one of the main causes we have found is that our table_cache was set too low, causing an ever increasing number of table opens. As we increased the table_cache, and watched for higher hit percentages, we were stumped regarding how many table opens in a given time period were acceptable. A number which I use as a guideline was given to me during a MySQL training course this year. We use a guideline of no more than 10 table opens per hour. More than that- and we need to increase table_cache.

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Human readable disk usage

by admin

Finding out what directories and files are using up the disk space on your server is fairly easy with du, but the output is not always easy to read.

However, it’s not too hard to pretty up the output with some perl and the module Number::Bytes::Human (available from CPAN). To convert normal du output into a more human readable form, which shows file size in the correct units (K, M, or G) and also includes the percentage of the total space each entry is using, use the follwing steps. Read the rest of this entry »

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Building a kernel RPM from source

by Michael Klatsky

While it is reasonably easy to build a kernel RPM on a Redhat or CentOS system using the kernel src rpm, another way is to do a standard kernel build (download your kernel from kernel.org), configure as usual. However, instead of just doing a standard “make” or “make bzImage”, do “make rpm“, and voila! You’ll be left with your kernel rpm in /usr/src/redhat/RPMS/{arch}, and your very own src rpm in /usr/src/redhat/SRPMS. Easy, right?

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