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You can often forget what you are not running as a super user, so if you type in a command that you can't run with your current set of privileges it will tell give you a permission denied response.
An alternative is to use the !! command to run the last command in the .bash_history. Use this with the sudo command to run the last command as a super user.
Timing web requests is possible in curl using the -w or --write-out flag. This flag takes a number of different options, including several time based options.
Creating a symlink is a common way of ensuring that the directory structure of a deployment will always be the same. For example you might create a symlink so that the release directory of release123/docroot will instead be just current.
I'm a proponent of automation, so when I find myself running the same commands over and over I always look for a way of wrapping that in an alias or script.
Grep is a really powerful tool for finding things in files. I often use it to scan for plugins in the Drupal codebase or to scan through a CSV or log file for data.
For example, to scan for user centric ViewsFilter plugins in the Drupal core directory use this command (assuming you are relative to the core directory).
Part of the process of putting a new site live can be moving DNS entries around. Prior to doing this it's a really good idea to sort out the Time To Live (TTL) of the DNS record so that when you do change DNS entries you aren't waiting around for a day for the DNS to sort itself out.