Jeff Epler's blog

31 January 2014, 18:05 UTC

Mosh automatic cleanup of dead sessions

I love mosh, using it to connect to a long-lived screen session from multiple computers (laptop, chromebook, $DAY_JOB, and phone).

One problem with it is that a mosh-server process that has no living client will linger for a very long time (forever?). This can happen for various reasons, such as letting a device's battery run down.

With some brainstorming help from the participants from #mosh, I came up with a way to automatically kill old mosh-server processes that probably represented defunct clients without killing ones that may represent working clients.

For a long time, my basic setup has been to run a command equivalent to: mosh myserver -- bin/cs where cs is a script which sets some environment variables and ends with exec screen, so I already had an excellent location to put cleanup code.

I also felt that the cleanup rule I wanted was: kill all mosh-server processes started from the same client. $SSH_CLIENT was suggested for this, but it's not useful since my portable devices naturally connect from different networks with different IP addresses (that's the point of mosh after all!) So I jumped to the conclusion that I needed a unique identifier. Why not involve a UUID?

As soon as I realized I needed to pass the UUID on the commandline or environment of cs, I realized that meant it would show up in the mosh-server commandline. So that led to the following snippet: ($i is already identified as being the UUID= argument):

    ps h --sort start_time -o pid,command -C mosh-server |
        grep "$i" |
        head --lines=-1 |
        awk '{print $1}' |
        xargs --no-run-if-empty -n 1 --verbose kill

That seems to work! One final wrinkle, though: In mosh irssi connectbot, there's no way to specify the mosh commandline directly. Hoever, there is "Requested mosh server". I created a wrapper script reading:

exec mosh-server "$@" -- bin/cs UUID=...
and used that script (with full path, in my case) as the configuration value.

Now I shouldn't have to worry about mosh-server processes piling up on my main linux box anymore.


20 May 2013, 21:37 UTC

tardiff: diff two (compressed) tar files without extracting

Recently I was googling for a script to compare tar files, and found references to a perl script (which I did not read) which reportedly did this by expanding both tar files and then diffing the trees. This would actually have been fine for my case, but some people noted that their use case involved tarfiles that were too big to extract comfortably. I assume that this is due to space considerations, but doubtless there are time considerations too.

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4 January 2013, 20:37 UTC

Screen-scrape ting device usage

Ting offers great inexpensive cellphone service, so when Ingrid's organization needed to provide a cellphone for an employee, I naturally suggested she use them. However, Ting doesn't presently have an API to check usage. So I put together a Python program that can screen-scrape this information.

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29 February 2012, 15:42 UTC

Half-maximize script for Linux

A number of times, I've said that I like the Windows 7 feature that allows a window to easily be half-maximized. I got tired of waiting for it to be added to my favorite window manager, so I wrote a script that uses the program wmctrl to half-maximize windows, then bound it to key presses in my window manager. Now, with a press of ctrl+alt+[QWER], I can half-maximize a window into 4 locations on my dual-monitor setup.

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