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Working on a server via SSH
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Working on a remote machine is a common task, when, for example, data mining or other long running jobs are put on a dedicated machine. Having some useful tools at hand is important, because SSH connections often close unexpectedly, for example on unstable WLAN connections.

Cool Shell Tools Configurations

Your shell should be configured such that it maximizes the amount of information you can get from a text-based representation. This includes color support and other sensible settings for the most important shell tools. A dedicated repository offers an installer for some important shell tool’s configuration files.

git checkout git://github.com/amaunz/home-bin
cd home-bin
./_init.sh

This will copy configuration files for different shell tools to your $HOME directory, including configuration for bash, vim, irb, git, screen, htop, and more. These configurations are designed to maximize productivity, customizing color support, syntax highlighting, command history, layout, among others. Explaining all options is beyond this document’s scope. See the configuration files for comments documenting the options.

Note: Your current settings are not overwritten. If, for any configuration file, a different configuration is already present, _init.sh opens a vimdiff (side-by-side editing) session, such that you can push and pull changes manually to your settings.

home-bin

See this tutorial to learn how to work with vimdiff.

Using htop

htop is an ncurses-based tool for monitoring CPU, RAM, load, and processes. See this tutorial.

Using GNU screen

Do not open several SSH sessions to accomplish several tasks. Any session creates load, while the server could use it’s CPU cycles and memory for other jobs, such as running your applications. Use a single SSH session only. It is less likely to be interrupted than many sessions at once.

Also use the “screen” utility. It even saves your work when your single SSH session is interrupted. This is how a screen session can look like.

home-bin

It shows two regions (a larger and a smaller one) on a single window. The status bar at the bottom includes hostname, windows list (currently 4), and CPU load (part of the cool shell tool configuration package).

Start screen session:

screen -S "screentitle"

This puts you inside a session called “screentitle”. Start only one session, then use as many windows as you want inside this screen session.

Working with several windows inside screen:

You can have several so-called windows inside a screen session, which you can imagine as tabs or sheets. You can switch between them. Every window inside a session is a full terminal. You can run different things on each window, just as you did previously with several SSH connections, but you need only one. If the single SSH connection fails, nothing is lost. Simply reconnect and re-attach to your screen session, then go to the right window.

  • Ctrl+a c Create new window
  • Ctrl+a k Kill the current window / session
  • Ctrl+a w List all windows
  • Ctrl+a 0-9 Go to a window numbered 0 9, use Ctrl+a w to see number
  • Ctrl+a Ctrl+a Toggle / switch between the current and previous window
  • Ctrl+a :fit Fit screen size to new terminal size. You can also hit Ctrl+a F for the the same task
  • Ctrl+a D Power detach and logout. Think twice before doing this!
  • Ctrl+a d Detach but keep shell window open. This is safe!
  • Ctrl-a ? Display help screen i.e. display a list of commands

You can also have so-called regions that split your screen window, so you can monitor different things at the same time.

  • Ctrl+a S Split terminal horizontally into regions and press Ctrl+a c to create new window there
  • Ctrl+a :resize Resize region
  • Ctrl+a tab Move to next region
  • Ctrl+a :remove Remove / delete region. You can also hit Ctrl+a X for the same taks

Scrolling

  • Ctrl+a esc Start scroll mode. Scroll up and down using the arrow or page up/down keys. Hit esc again to leave scoll mode.

Leave screen session (but keep it running in the background):

Inside screen, press Ctrl+a d. This detaches the screen session and runs it in the background. The same happens if your connection is interrupted.

Re-attach to screen session:

screen -ls  # show running session names as PID.screentitle
screen -r PID.screentitle  # re-attach to sesssion

You should be back to your session named “screentitle”.

home-bin

Try it: open a screen session on a remote machine, then pull the network cable.

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Published

28 July 2012

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