Time Management for System Administrators

merged file to the legacy masters as if it were their own. I continued this process for each file or database.

Since each change was small and specific, I could test it incrementally. After literally hundreds of small changes, all the servers were 'singing from the same songbook.' At that point, it was easy to eliminate the legacy masters and let the new master be the authoritative master for all clients.

Warning

Any file that is automatically pushed to other servers should always have a comment at the top of the file warning other system administrators where the file came from and where to edit it.

Here's the warning I use: # THIS FILE IS MAINTAINED ON: server1.example.com # Edit it with this command: xed file.txt # If you edit this file on any other machine, # it will be overwritten. BE CAREFUL!

Since the previous note mentioned xed, I should explain what it is. There are many programs called xed, but this one can be found on http://www.nightcoder.com/code/xed. This program calls whatever editor you usually use ($EDITOR can be set to vi, pico, emacs, and so on) after locking the file. It is a must for any site that has multiple system administrators working on the same machine. If you are using RCS to track changes to a file, it does all the 'check in' and 'check out' work for you. This gives you infinite undo and a logfile of who changed what. If you find that a system has been acting funny for the last month, just check the log to see who changed the file a month ago and, well, be nice—we all make mistakes.

Hard Things Done Once

When we find ourselves doing something very difficult, automating the task records what we've done. When we do it in the future, it will be easier. This is how we build up our little bag of tricks.

Encapsulating a Difficult Command

Sometimes it takes hours to work out exactly the right command required to do something. For example, there is a program that creates ISO images, the kind you burn onto CD-ROMs. Its manual page describes hundreds of options, but to make an image readable by Windows, Unix, and Mac systems, the command is simply: $ mkisofs -D -l -J -r -L -f -P ' Author Name ' -V ' disk label ' -copyright copyright.txt -o disk.iso /directory/of/files

Sure, you can do it from a GUI, but where's the fun (or ability to script) in that?

This command also lets you do things not found in most GUIs, such as the ability to specify a copyright note, author name, and so on.

This is a good example of something to work into a .BAT file (DOS) or a Unix/Linux shell script.

Here's a shell script called makeimage1 that uses this: #!/bin/bash mkisofs -D -l -J -r -L -f -P 'Limoncelli' -V 'date -u +%m%d' $*

The 'date -u +%m%d' sets the volume name to the current date.

One of the things that held me back from writing good scripts was that I didn't know how to process command-line parameters. Here are instructions for copying all the command-line arguments into a script.

The $* in the makeimage1 script means 'any items on the command line.' So, if you typed: $ makeimage1 cdrom/

then the $* would be replaced by cdrom/.

Since $* works for multiple arguments, you can also do: $ makeimage1 cdrom/ dir1/ dir2/

Then the $* would be replaced by all three components. In the case of mkisofs, this would merge all three directories into the CD-ROM image. You can refer to $1, $2, and so on, if you want to refer to specific items on the command line.