How many times has this happened to you?
startup-config file open failed (Device or resource busy)
If you work in an environment where multiple users have enable access on Cisco devices, you've probably seen it more than once. This particular error is caused when another user has locked the startup-config file by running 'show start' (short for 'show startup-config') or 'show config' (sort for 'show configuration'). When you are trying to get work done, this is a major annoyance (especially if the person that locked the file has run out for a "quick" lunch).
You're likely thinking, "It's reasonable to expect users to look at the configuration!" And right you are. The problem is that 95% of the time, you are interested in seeing the running-config ('show run'). On a normal basis, the configuration of the system when it reboots is much less interesting (although usually exactly the same) as how the system is running at the moment. In fact, by using 'show config', you missed the changes that I just made and am trying to save!
What you should take away from this is that 'show config' should only be used in those special circumstances when you need to see how the system will reboot. Otherwise, 'show run' will have the configuration you need and not disrupt other workers.
Note: Do not be fooled by the 'service multiple-config-sessions' command available on some platforms (the Cisco 7500 series, for example). This controls the ability to open up multiple configuration sessions, not multiple views of the startup-config.