Here is a short list of categories, roughly in order of increasing level of difficulty to recover.

• Backups and off-site storage
• RAID
• Documents
• File Systems
• Data Recovery from Hard Drives

There is software available that can recover from several types of failures, but it does not always work when there is corruption, or failure of disk drives, media or other hardware. Not only that, but recovery can cost hundreds of dollars for each disk, and is not guaranteed to recover any data. This is why backups are essential. If you are not a sysadmin, and just have a single computer to work on, there is probably some data that you consider important. If nothing else, copy it to another location such as a USB drive, another computer, a CD, or an ftp site.

Reliable Backups

Obviously, when there are reliable backups, there should be little difficulty in restoring the data, but it may not be as easy as it sounds. Some of the problems with backup and restore procedures could be:

• The data may be outdated.
• The missing data may not have been backed up yet.
• The tape or other media may fail.
• The tape, or media may not be found because it was misfiled, mislabeled, or too old to keep.
• The time lost in restoring data may be important.
• The backup software may have failed, or not been setup properly.
• Directories, drives, or systems may not have been selected to be backed up.
• The backed up files may have been corrupted, or infected with a virus.

An important part of disaster recovery is reliable backups. How can the backups be verified? Try a restore once in a while to make sure it is working properly. I have seen restores fail when backed up on one file system, and restored to another. The file was restored, but the data was corrupt. It took a while to figure out, but when an Excel file was backed up from Netware and restored to NT some of the cells were corrupted. Another time a problem was noticed when attempting to restore. Some new directories had not been selected to be backed up. Sometimes software will allow you to select directories, but will not automatically include subdirectories. These are the types of things that should be tested by attempting to restore once in a while.

RAID Systems

One of the best inventions for sysadmins was the RAID system. RAID, or a Redundant Array of Inexpensive Disks provides a means to quickly recover data in the event of a drive failure. In normal operation, systems will use RAID 5, which includs three or more disks in an array. When any one drive fails, the system continues to function normally, and the drive can be replaced at the leisure of the system administrator. If it was on good hardware, there is usually no downtime. The drive can be “hot-swapped”, meaning that the defective drive can be removed, the replacement drive inserted, and the array rebuilt — all without taking down the computer system.

Here is an example of how RAID arrays saved time when moving servers. We had a couple dozen servers to move across town, and were concerned about the data on the drives as the servers were moved. There were reliable weekly and daily backups, but the current day had not been backed up. The standard tape backup process would take several hours. The solution was to remove a drive from each system, and replace it with a spare. How did that work? Each system had a RAID 1 array, which consists of two mirrored SCSI drives. Removing one drive gave us an instant backup that could be used to restore the array in case the other drive failed while being transported. Replacing the drive with a spare caused the array to rebuild in a matter of minutes, so that there was even less chance of failure. Of course we were careful in moving the hardware, and none of the drives failed, but we saved several hours of time-wasting tape backups. All we had to do was reconnect the servers, and assign new IP’s of course, and then let the nightly tape backup continue as scheduled.

Document Autosave

Documents are in a little different category of data recovery, since we are discussing recovery of documents that have not been backed up by the daily backup process. It is common to be working on a document during the day, and have backups run at night. If there is a corruption, or crash while working on a new document, there may be a way to recover the most recent work. We will look at vi as an example, but other text editing, and word processing software often have a similar feature.

Using Autosave in vi.

Documents are automatically saved in vi, but it is still a good idea to save your work as you go. Simply type Esc:w! to save the current file.

Try this. Open a file, and type some text.

$vi test.txt
i
This is a test
Esc:wq!

Now look at the directory.

$ ls -a
. .. .test.txt.swp test.txt test.txt~

Notice that there is a hidden swap file, your original file, and a backup file. Vi will automatically delete the file on exit, or use the file, if it still exists the next time you open the original file. The file ending with a tilde ~ is the auto-save version of the file, which may or may not have the latest data in case of a crash.

File Systems

File system integrity can be handled with several utilities, each of which could have a discussion of their own.

One of the most commonly used Linux utilities is fsck. The fsck utility will run automatically at boot up if it detects that it has not been run in a while, or if the system was not shut down properly. More advanced users will need to learn this and other utilities which can be run on unmounted file systems, often from a boot disk. Be careful about running fsck on mounted drives, or RAID arrays.

Data Recovery Software and Services

Before resorting to a data recovery service, it may be worth the time to look for some software that can recover the data you need. A data recovery service can be helpful when there is no other way to retrieve the data. They are able to open drives that do not spin, and read them with a microscope, but the process can cost thousands of dollars. If the data can be recovered by using software, the recovery service may be able to restore the data for a few hundred dollars. Wait a minute. If they are using software, can’t I do the same thing? The short answer is – maybe. Some software is free, and some costs several hundred to several thousand dollars. As our readers know, we love free open source software. The first thing to try is some of the recovery software, and boot disks listed on freshmeat.net. Then search for data recovery software on search engines such as google, bing, or yahoo. If the free ones don’t work, some of the other might do the trick, but the free software should at least show that a partition exists on the drive, and that there might be something to recover. Rem
ember, if the hardware is noisy, or unreliable, it is best to take it to a data recovery service, and not keep it powered on.

Nagios is more than just a server monitoring tool. From the Nagios website: “Nagios is a powerful monitoring system that enables organizations to identify and resolve IT infrastructure problems before they affect critical business processes.”

Systemnotes.org download:
http://www.systemnotes.org/download/shell/nagios-config-build.html

Freshmeat project: http://freshmeat.net/projects/nagios-config-build

Please feel free to use this blog post for comments, or questions.

Here is a high level overview on how to use the macro recording feature of vim.

High Level Steps to Record and Play a Macro in Vim

1. Press q to Start recording, followed by a lower case character to name the macro.
2. Perform any typical editing, actions inside Vim editor, which will be recorded.
3. Stop recording by pressing q.
4. Play the recorded macro by pressing @ followed by the macro name.
5. To repeat a macro multiple times, press : n @ macro name, where n is a number.

For more details, check out a complete tutorial at thegeekstuff.com: Vim Macro Tutorial: How To Record and Play

This is not a comprehensive list, but a few shortcuts I find myself using all the time.

Bash Shell shortcuts

• Shift-PageUp / PageDown See more of the screen
• Ctrl-a, Ctrl-e Move to beginning / end of line
• up & down arrows See bash history
• !! / !$ Execute the previous command / parameter
• !n Execute the nth command in history
• Ctrl-D Logout, or exit
• Ctrl-u, Ctrl-h, Ctrl-b Delete previous char, or entire line
• Alt-F1 to Alt-F7 Switch to another console
• —see also: using-bash-history, and all bash posts

X shortcuts

• Ctrl-Alt-Backspace Force X to reset
• Alt-tab Switch to a different application
• gnome-terminal:
  • Ctrl-Shift-t Open a new tab
  • Ctrl-PageUp / PageDown Switch between terms
  • (Ctrl)-Alt-F1 to F7 Switch to another console (Ctrl while in X)

Firefox shortcuts

• Ctrl-Click / Shift-ClickOpen link in new tab / window
• Ctrl-PageDown Goto next tab
• Ctrl-t New tab
• Alt-Home Goto home page
• Esc Stop flash animations from playing
• Ctrl-Shift-t Re-open a Recently Closed tab

There is a nice shortcut list at linuxhelp.blogspot.com, organized by key bindings http://linuxhelp.blogspot.com/2005/08/bash-shell-shortcuts.html

To add an alias to your .bashrc file:

$ vi ~/.bashrc

Insert these lines:

alias ls=’ls –color=tty’

alias ll=’ls -l’

In order for the new alias to take effect, you can open a new console, login again, or simply source your .bashrc file. You also have the option of running bash again to open a new shell, or just running the alias command. What do I mean by source the file? You can either run a script, or have the shell read the variables in a script without actually running it. This is called sourcing a file, and is accomplished by typing either “source”, or “.” followed by the file to source, e.g.

$ source ~/.bashrc

or

$ . ~/.bashrc

Sometimes the word source is easier to read than a dot, but either method will work fine.

Note that you don’t need to be root to access your home directory. “~/” is a shortcut for wherever your home directory happens to be (e.g. /mountpoint/home/me, or /home/users/someone). Also, the dot “.” is used for hidden files, so if you do

$ ls ~/

it won’t show up, but if you do

$ ls -a ~/

it will.

There are some common aliases you may have by default. To view your current aliases, type alias by itself, or “alias -p”:

$ alias -p
alias cp=’cp -i’
alias l.=’ls -d .* –color=tty’
alias ll=’ls -l –color=tty’
alias ls=’ls –color=tty’
alias mv=’mv -i’
alias rm=’rm -i’
alias vi=’vim’

Other Uses

“What else can this be used for?”, you ask. Anything you use often enough — usually something smaller than a script, but too long to type frequently. How about changing to a common directory? Of course, to go home, type:

$ cd

To go to the previous directory, type:

$ cd -

Maybe you would like something like “sales” to take you to /home/dept/sales.

alias sales=’cd /home/dept/sales’

Unalias

What happens if you make a mistake, or you use your account on a host that has a shell that does not support your alias? For example, you log into a sun box, and the ls alias is not valid. The quick fix is to simply run “unalias ls.”

So, go have some fun with aliases. Here are a few ideas to try:

alias h=’hostname’
alias myprogram=’/usr/local/bin/myprogram’
alias taillog=’tail -f /var/log/messages’
alias which=’alias | /usr/bin/which –tty-only –read-alias –show-dot –show-tilde’

There is another problem that can cause a shell or xterm to freeze. If you ssh to a remote host, and then logout, sometimes the session will freeze. In that case, all you need to do is type “Enter”, “~”, “.” (Enter, Tilde, Dot with no spaces) to get the console back. That’s the Enter key, immediately followed by tilde “~”, and then a period “.”

[Enter]~.

Also, a convenient way to exit a shell, xterm, or remote ssh terminal is to use Ctrl-D rather than taking the time to type the word “exit.”

This is user specific, so you’ll have to find your own home directory under ~/.mozilla/firefox/. Mine is dz4bq7je.scottm on this host.

$ cat ~/bin/unlock_firefox.sh
#!/bin/sh
rm ~/.mozilla/firefox/dz4bq7je.scottm/.parentlock
rm ~/.mozilla/firefox/dz4bq7je.scottm/lock
$ ll ~/.mozilla/firefox/
total 12
drwx—— 9 scottm users 4096 Sep 9 11:25 dz4bq7je.scottm
-rw——- 1 scottm users 1264 Jun 23 2008 pluginreg.dat
-rw-r–r– 1 scottm users 162 Nov 15 2005 profiles.ini
$

The advantage of this simple script is that you don’t have to go looking for directories and files, or remember where firefox puts them. Just remember when it’s locked, look for your unlock script.

The idea is similar in many different email programs.

Easy Two Step Process

There are two simple steps to help your recipients avoid getting flooded with spam.

1.) Enable the Bcc feature

2.) Use “Bcc:” instead of “To:” whenever sending mail to multiple recipients.

Screen Shots

Step 1.) Find and Enable the Bcc feature

Step 2.) Use Bcc:

That’s all there is to it! You’ll be saving your friends from tons of unwanted emails by keeping their email addresses private.

For more details on why BCC is important, please see this article:

http://systemnotesorg.blogspot.com/2008/02/bcc-howto.html

RHCE-Flash-Cards

These notes should be helpful to anyone working on Redhat Enterprise Linux (RHEL), or preparing for the RHCE exam.

My RHCE Study Guide was hugely popular, but unfortunately it had some potential copyright issues. This group of flashcards has also been released as a quick study guide, or cheat sheet, and contains much of the same original study guide material, but with all proprietary information removed. This 3-page guide is listed as RHCE Flash Cards (condensed version)

How These Slides Were Created

These slides were produced using OpenOffice.org Impress.

1. Created Slides
2. Saved as html
3. Copied contents of html between body tags to .page files.
   • Used a bash shell script with sed, and awk to get the files to appear properly for webgen. See script here—html2page.html
4. Ran webgen on the directory to generate .html

Also .pdf files were saved from Openoffice.org Writer, which not only is free software, but also allows writing of .pdf files — also for free. Isn’t open source software great?

Let us know what you think.

If you notice any errors, omissions, or potential copyright issues, please comment below, or contact us.

We can’t have all work and no play, so a cartoon every once in a while doesn’t hurt. While you’re having fun, check out http://www.lifeisnojoke.com.

Here are some articles on where to find free software:

opensource-software-for-windows

searching-for-software

Now, some people may not understand that by free, we mean free. Not pirated, illegally copied, or borrowed. Open source software is free to use, copy, modify and distribute.

A small to medium-sized company may have 100 computers, and have to pay $200 for some kind of office software for each machine for a total of $20,000. But if the company chooses to use free software such as openoffice, the price would be $0.00 x 100 = $0.00.