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What is the equivalent of clear line con 0 in Cisco IOS?

I'm using serial-getty@ttyS0.

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    Questions like "What is the equivalent of command X on system Y" are always hard to answer because there are usually a lot of very fine details of what, exactly, command X does, that can't be 100% replicated. However, it is also likely that you are not really interested in replicating command X 100%. Rather, you have a problem you want to solve, and you know, on system Y you would solve that problem with command X, so you ask about an equivalent to command X. But maybe, the equivalent to command X isn't even the right command to solve the problem! So, rather ask about the problem instead. Commented May 5, 2024 at 16:31
  • Thank you for your advice. I did choose that question because it conveys better what I was thinking about. I had not known about the loginctl list-sessions command. I had not known about pkill's --terminal option. Those solutions allow me to rewire my brain. Commented May 6, 2024 at 5:31

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In Cisco IOS, clear line con 0 apparently kills an existing serial console session.

The closest low-level equivalent would be to send a SIGHUP to all processes on a particular TTY device. So:

pkill -HUP -t ttyS0

If there is a process that is designed to evade a SIGHUP, you could escalate by removing the -HUP option to use a regular SIGTERM instead, or even further by using SIGKILL with -KILL.

The above method should work irrespective of init system used.

A SIGHUP essentially tells the system that a TTY connection that used a modem was disconnected. With it, most editors (or any programs designed to save the user's work in case of an accidental disconnection) would likely save a backup copy of any unsaved data to minimize the risk of losing work. With SIGTERM, it is more likely that any unsaved work is simply lost; with SIGKILL, any unsaved work in a session that gets terminated will be lost for sure.

Since you seem to be using systemd, a higher-level way to do it would be to use loginctl list-sessions to find the session ID number of the current session on ttyS0, then loginctl kill-session <session ID> to force that session to end.

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  • What a great answer! Both solutions work fine, and both resemble that command I'm accustomed to. Commented May 5, 2024 at 20:47

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