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Jimm Chen
Asked: 2020-03-13 08:22:49 +0800 CST

crontab + SSH client, disk space leaking problem, how to solve it?

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I'm using Ubuntu 18.04 LTS, and I'm doing something weird on my system.

In crontab -e, I have a line like this:

@reboot sleep 11 && sshpass -p '123456' ssh -D *:7070 socksclient@localhost

so that an ssh client program runs automatically on system startup, acting as a SOCK5 server at port 7070.

But something bad happens. My root partition is slowly running out of space, and I can see this leakage with df, about 100 bytes per second.

After some investigation, lsof | grep deleted reveals that it is ssh or sshpass grabbing [ a file handle to a deleted file-system path(/tmp/#16 in the attached image)] and append content to it continuously, so it is sneakingly hogging my disk space.

Snap0651 lsof grep delete chh tip.png

BTW: If I run sshpass -p '123456' ssh -D *:7070 socksclient@localhost manually from Linux console, those (delete) entries will not appear.

Those leaked disk space can not be revealed with du, and, they can be freed only by killing the ssh or sshpass process.

So my question is: I want my ssh client to run with system startup, but eliminate disk space leakage. How to achieve that?

I'll be appreciative if someone can tell:

  • What's the current size of a deleted file?
  • how can I know what content(text) is being appended to the /tmp/#16 file? Maybe some program similar to the Process Monitor on Windows?
ssh cron

1 Answers

  1. Best Answer

    hope this help.

    Get the PID and FD of process holding that 'deleted' file/fd and use stat/cat/peekfd etc. It has to be still running cause file even in deleted state is here (under active process).

    $ ps uax | grep "your process name" #to get the PID

    $ lsof -p "PID id You found" #to see open files and their FD

    $ stat /proc/${mypid}/fd/${myfd}

    $ cat /proc/${mypid}/fd/${myfd}

    $ peekfd /proc/${mypid}/fd/${myfd}

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