One of the main tasks of any administrator is to create stable environment for different sorts of businesses. Big part of this task is troubleshooting. There are many different tools in UNIX for system monitoring, but, at my mind, one of the most useful tools is lsof- one of the least-talked-about tools in a UNIX sysadmin’s toolkit. Lsof lists information about files opened by processes. But that’s really an understatement.
Most people forget that, in UNIX, (almost) everything is a file. The OS makes hardware available to applications by way of files in /dev. Kernel, system, memory, device etc. information in made available inside files in /proc. TCP/UDP sockets are sometimes represented internally as files. Even directories are really just files containing other filenames.
Lsof works by examining kernel data-structures and provides a variety of information related to files, pipes, sockets and more.
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Sometimes, I need to connect remote Unix servers with tunnels to provide some specific services or to get access to some internal networks. I was very surprised, when my friend, young system administrator, asked me about how to bring up IP-IP tunnel between different Unix operating systems (FreeBSD and Linux in his case) and said, that he can’t find information about this configuration. As the result of my discovering, this HOWTO has been created.
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Some times we need to debug some web-application or some web-server software, but we can not see complete HTTP-session. I very like Live Headers Plugin for Firefox, but it has some disadvantages… It can not say me when some interesting event happens.
Let me introduce very useful tool for web-server admins and web-developers: Fiddler – HTTP Debugging Proxy which logs all HTTP traffic between your computer and the Internet. Fiddler allows you to inspect all HTTP Traffic, set breakpoints, and “fiddle” with incoming or outgoing data. Fiddler is designed to be much simpler than using NetMon or Achilles, and includes a simple but powerful JScript.NET event-based scripting subsystem.
If you need to debug HTTPS headers, you can use RPASpy plugin that enables viewing HTTPS request and response headers inside Fiddler.
Lewis Cunningham wrote very detailed article about Oracle Database 10g Express Edition (XE), about limitations of this version of Oracle and about specific areas where Oracle XE will be ideal solution.
Let me describe basic Oracle XE limitations:
- Memory – Oracle Database XE can address only 1GB of RAM.
- CPU – Oracle XE will only use one CPU.
- Instances count – Only one instance of Oracle XE can run on any given computer.
- Disk Space – You can only use up to 4Gb of disk space for your data.
At my mind, Oracle XE can be good replacement for poor MySQL database and slow PostgreSQL database servers in some areas. I’m using it in billing system of middle-sized ISP and I really glad to have possibility to use such powerful database for free.