Tag Archives: terminal

Terminal annoyances

Posted on by

Largely for legacy support reasons, terminal emulators and consoles include a few features that were useful on older terminal systems, but that are not needed or even a hindrance today. Perhaps chief among these is the legacy of flow control characters, referred to in the stty manual as “XON/XOFF flow control”. With this enabled, as it is by default on many systems, pressing Ctrl+S in a terminal will prevent both input and output of characters until terminal writing is resumed again with Ctrl+Q. For people not aware of this feature this can be disconcerting, as the terminal apparently simply freezes and won’t come unstuck; if you’re on an SSH connection you may incorrectly think there’s a network problem.

While this may still have some limited applications, with slow serial terminals more or less a thing of the past it’s mostly just annoying, particularly when using applications that are very heavy on Ctrl chords, and especially when you use GNU Screen or some other terminal multiplexer with Ctrl+A as the prefix key that invites fat-fingering Ctrl+S. You can turn flow control off completely by including this stty call in your .bashrc:

stty -ixon

This also frees these keys up for other uses, such as being bound in Vim or Emacs, or for the forward incremental history search feature in Bash, which I find much more useful.

Similarly annoying is the beep emitted from the PC speaker under some circumstances when using the console, for example when pressing Tab to invoke Bash autocompletion when no further completions are available. I also prefer to turn this off, which can be done with:

setterm -bfreq 0

I don’t find myself missing either feature, though I’m told a few people still find flow control handy in some circumstances. There’s ongoing interest in disabling the feature by default in certain distributions.

Watching with tmux

Posted on by

watch is one of those Unix tools which does something very simple, but combined with other tools has a myriad of uses. While there are a few useful features or switches for watch, its central concept is simple; it runs something for you repeatedly, and shows the output on the screen.

The reason this becomes so useful in a system administration context is that when used with a terminal multiplexer, watch can be used to track the progress of any particular task, or to monitor system resources, as you work and change things. Some examples of simple but useful monitoring tasks are:

  • Load average — watch uptime
  • Disk space — watch df -h
  • Process count — watch 'ps -ef | wc -l'
  • Memory usage — watch free -m
  • Size of a volatile file — watch du -sh filename.sh

Of course, it’s not a terribly good use of an administrator or developer’s time to just sit there and watch these change, particularly if you want to make changes to the system or application and see how they affect the results of your monitoring. This is where a terminal multiplexer like tmux comes in handy, for putting instances of watch and other more complex monitoring tools like htop or tload into independent panes of a terminal window so you can work as you watch them.

Monitoring tasks running in tmux

Monitoring tasks running in tmux

You can set these windows up using the usual key combinations, but if you have a long string of text or a known command that you want to start running in another window, it’s often easier to call the relevant tmux commands directly from the shell:

$ watch uptime
$ tmux split-window -dh "!!"

This will split the window into two parts, and run watch uptime in the new one, while leaving your cursor in the original window.

If you find yourself doing this often, you could make it into a shell function in your .bashrc or similar:

function tmw {
    tmux split-window -dh "$*"
}

You can then quickly run things like the following, as a kind of general method to background a monitoring or long-running task quickly:

$ tmw watch uptime
$ tmw htop
$ tmw rsync -arvz source::mnt/location /home/tom/destination

Thanks to user WishCow for pointing out an error in the comments.