Archivio tag: troubleshooting

Bookmarks for 26 ago 2014 through 27 ago 2014

These are my links for 26 ago 2014 through 27 ago 2014:

  • Regular Expressions – Regular expressions ("regexes") are supercharged Find/Replace string operations. Regular expressions are used when editing text in a text editor, to: check whether the text contains a certain pattern find those pattern matches, if there are any pull information (i.e. substrings) out of the text make modifications to the text. As well as text editors, almost every high-level programming language includes support for regular expressions. In this context "the text" is just a string variable, but the operations available are the same. Some programming languages (Perl, JavaScript) even provide dedicated syntax for regular expression operations.
  • MySQL active-passive cluster | Your IT goes Linux – We will use the iSCSI Lun defined in our iSCSI cluster as a shared storage and we will run MySQL in active-passive (fail-over) mode using Pacemaker and Corosync cluster engine. The cluster will have to connect to the iSCSI target, mount the iSCSI partition on one node and start a MySQL service which has all its data on this partition.
  • Perl – [...] Perl has horrors, but it also has some great redeeming features. In this respect it is like every other programming language ever created. This document is intended to be informative, not evangelical. It is aimed at people who, like me: dislike the official Perl documentation at for being intensely technical and giving far too much space to very unusual edge cases learn new programming languages most quickly by "axiom and example" wish Larry Wall would get to the point already know how to program in general terms don't care about Perl beyond what's necessary to get the job done. This document is intended to be as short as possible, but no shorter[...]
  • Linux Performance – This page links to various Linux performance material I've created, including the tools maps on the right, which show: Linux observability tools, Linux benchmarking tools, Linux tuning tools, and Linux observability sar. For more diagrams, see my slide decks below.
  • AIXchange: Useful Storage Links – Here's an assortment of really good storage-related articles — the majority of which are found on IBM developerWorks — that are worth your time. While some of them are a few years old, they still provide relevant information.

Bookmarks for 30 apr 2014 through 6 mag 2014

These are my links for 30 apr 2014 through 6 mag 2014:

  • Ralentir le débit de postfix pour wanadoo/orange – Le blog de Michauko – Si vous avez un serveur d’envoi de mails (je ne parle pas d’être un spammeur) et beaucoup d’abonnés chez Wanadoo et Orange, vous risquez fort le rejet temporaire de votre serveur si le débit d’envoi est trop fort. C’est ce qui m’est arrivé et hop, 5000 mails entassés dans la file de postfix.
  • refused to talk to me: postfix solution | – Orange sadly limits inbound connexion to it’s MX to 1 connexion per IP, which is a total pain in the ass when you try to deliver newsletter, or manage a MTA. Here is a sample log from their MX: Jul 4 10:42:42 postfix/smtp[32347]: 0123456789: host[] refused to talk to me: 421 mwinf5c34 ME Trop de connexions, veuillez verifier votre configuration. Too many connections, slow down. OFR004_104 [104] However, since they won’t change anything, we have to take mesures, here’s what you can do if you run postfix: you have to set a per-destination concurrency limit.
  • Aral Balkan: Historical Archive — How to revert (roll back) to a previous revision with Subversion – Here, then, is a very simple, plain English explanation of how to revert to a previous version of your application in Subversion, to help anyone who may be starting out with it and is lost.
  • Tmux: A Simple Start – In all likelihood, you’ve probably already heard of tmux. However, you may not be using it everyday. If tmux is on your “Someday” list because you think it is too complicated (I mean, c’mon, the word “multiplexer” is just plain scary), then I am here to show you just how easy it is to put tmux into your workflow.
  • Tyblog | Yet Another Vim Setup – Vim is an excellent text editor. I’ve used it for many years and like most vim users, have collected a fairly large collection of settings in my .vimrc and learned how to grok my vim usage effectively through a lot of trial and error. To that end, I’ve tried to assemble a useful overview of my experience with vim.

Bookmarks for 18 apr 2014 through 30 apr 2014

These are my links for 18 apr 2014 through 30 apr 2014:

  • JoshData/mailinabox · GitHub – Mail-in-a-Box helps individuals take back control of their email by defining a one-click, easy-to-deploy SMTP+everything else server: a mail server in a box.
  • SSH Multi-hop Connections With Netcat Mode Proxy | Click & Find Answer ! – Since OpenSSH 5.4 there is a new feature called natcat mode, which allows you to bind STDIN and STDOUT of local SSH client to a TCP port accessible through the remote SSH server. This mode is enabled by simply calling ssh -W [HOST]:[PORT] Theoretically this should be ideal for use in the ProxyCommand setting in per-host SSH configurations, which was previously often used with the nc (netcat) command. ProxyCommand allows you to configure a machine as proxy between you local machine and the target SSH server, for example if the target SSH server is hidden behind a firewall. The problem now is, that instead of working, it throws a cryptic error message in my face: Bad packet length 1397966893.Disconnecting: Packet corrupt
  • Tyblog | SSH Kung Fu – OpenSSH is an incredible tool. Though primarily relied upon as a secure alternative to plaintext remote tools like telnet or rsh, OpenSSH (hereafter referred to as plain old ssh) has become a swiss army knife of functionality for far more than just remote logins. I rely on ssh every day for multiple purposes and feel the need to share the love for this excellent tool. What follows is a list for some of my use cases that leverage the power of ssh.
  • Baseimage-docker: A minimal Ubuntu base image modified for Docker-friendliness – YOUR DOCKER IMAGE MIGHT BE BROKEN without you knowing it Learn the right way to build your Dockerfile.
  • NetApp – Index – The following documentation is a guide on using and configuring the NetApp servers, there is also a commandline cheat sheet. I have tried to make this section as brief as possible but still cover a broad range of information regarding the NetApp product but I point you to the Official NetApp web site which contains all the documentation you will ever need.

Bookmarks for 28 mar 2014 through 29 mar 2014

These are my links for 28 mar 2014 through 29 mar 2014:

  • LDAP org chart | – For centralised authentication and authorisation, LDAP is the de-facto standard. Whether in its pure form on Unix or in Active Directory guise on Windows, everyone uses it. What many people don't realise is that you can store all sorts of useful (and not so useful) information in LDAP. One field which can be useful is the "manager" attribute. One of our customers use that and so we've written a small script to graph it using the excellent Graphviz tool. It will probably need customising for specific cases, however we hope that people find it useful nonetheless. If you want to alter the output, do have a look at the record format documentation.
  • Puppet errors explained | – Puppet is a wonderful system automation tool, however the learning curve can be a little steep. We've collected some of the errors messages and "strange" behaviour you may come across together with explanations to help overcome these hurdles and boost adoption of this fabulous tool. If you have any useful errors and explanations, please do send them in and we'll update this article.
  • SCAP: Guide To The Secure Configuration of Red Hat Enterprise Linux 5 – This guide has been created to assist IT professionals, in effectively securing systems with Red Hat Enterprise Linux 5.
  • DNS Load Balancing and Using Multiple Load Balancers in the Cloud – [...] Load balancing in general is a complicated process, but there's some secret sauce in managing DNS along with multiple load balancers in the cloud. It requires that you draw from a few different sets of networking and “cloudy” concepts. In this second article in my best practices series (my first post covered how to use credentials within RightScale for storing sensitive or frequently used values), I'll explain how to set up load balancers to build a fault-tolerant, highly available web application in the cloud. Here's what you’ll need: Multiple A records for a host name in the DNS service of your choice Multiple load balancers to protect against failure [...]
  • gdnsd – gdnsd is an Authoritative-only DNS server which does geographic (or other sorts of) balancing, redirection, weighting, and service-state-conscious failover at the DNS layer. gdnsd is written in C using libev and pthreads with a focus on high performance, low latency service. It does not offer any form of caching or recursive service, and notably does not support DNSSEC. There's a strong focus on making the code efficient, lean, and resilient. The code has a decent regression testsuite with full branch coverage on the core packet parsing and generation code, and some scripted QA tools for e.g. valgrind validation, clang-analyzer, etc. The geographically-aware features also support the emerging EDNS Client Subnet draft for receiving more-precise network location information from intermediate shared caches.