How to set ssh timeout?

Question

I'm executing a script connecting via password-less SSH on a remote host. I want to set a timeout, so that if the remote host is taking an infinite time to run, I want to come out of that ssh session and continue other lines in my sh script.

How can I set a timeout?

This should probably be closed to be in line with the closing of a complete duplicate of this how to decrease ssh connection timeout value [closed] — Murmel
– Murmel, Commented Jan 15, 2018 at 22:01
If you redirected here only to "stay more time in your ssh session" (question "How to increase SSH Connection timeout?"), this is the wrong place. The answer is at this link about ssh-timeout. — Peter Krauss
– Peter Krauss, Commented Feb 14, 2018 at 10:04

Eric Leschinski · Accepted Answer · 2020-03-07 03:05:43Z

476

ssh -o ConnectTimeout=10  <hostName>

Where 10 is time in seconds. This Timeout applies only to the creation of the connection.

edited Mar 7, 2020 at 3:05

Eric Leschinski

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answered Mar 10, 2011 at 4:41

user57421

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3 Comments

Mmmh mmh Over a year ago

ConnectTimeout only sets a timeout on the connection setup, right?

Ferry Boender Over a year ago

This doesn't actually work for "the remote host is taking an infinite time to run": "ssh -o ConnectTimeout=5 host 'sleep 10'" waits for 10 seconds, not 5.

laconbass Over a year ago

@FerryBoender It seems obvious that ConnectTimeout affects only the connection. Your example connects with success.

Doug · Accepted Answer · 2016-02-21 15:35:43Z

125

Use the -o ConnectTimeout and -o BatchMode=yes -o StrictHostKeyChecking=no .

ConnectTimeout keeps the script from hanging, BatchMode keeps it from hanging with Host unknown, YES to add to known_hosts, and StrictHostKeyChecking adds the fingerprint automatically.

**** NOTE **** The "StrictHostKeyChecking" was only intended for internal networks where you trust you hosts. Depending on the version of the SSH client, the "Are you sure you want to add your fingerprint" can cause the client to hang indefinitely (mainly old versions running on AIX). Most modern versions do not suffer from this issue. If you have to deal with fingerprints with multiple hosts, I recommend maintaining the known_hosts file with some sort of configuration management tool like puppet/ansible/chef/salt/etc.

edited Feb 21, 2016 at 15:35

answered Jul 1, 2012 at 16:37

Doug

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5 Comments

Dolph Over a year ago

Not only does -o StrictHostKeyChecking=no not address the question, but it's a terrible idea if you care about security, which might be the reason you're using SSH in the first place.

Doug Over a year ago

It is good to point out the possible security implications of -o StrictHostKeyChecking=no. However, it will prevent the script from hanging during execution.

johndodo Over a year ago

WARNING!!!! As @Dolph wrote, do NOT use StrictHostKeyChecking=no if you care about security at all. @Doug: script will not hang - it will just insist that you ssh to remote host manually the first time, so it gets to know the host. But it will protect you against MITM attacks. Please edit this answer to reflect this as it is a very dangerous advice as it stands. And it wasn't even asked for.

Doug Over a year ago

Updated my answer. From my experience, it can cause some clients to hang.

Steven de Salas Over a year ago

Use -o StrictHostKeyChecking=accept-new if you really must. As per this answer

Lee HoYo · Accepted Answer · 2015-11-06 14:24:42Z

77

try this:

timeout 5 ssh user@ip

timeout executes the ssh command (with args) and sends a SIGTERM if ssh doesn't return after 5 second. for more details about timeout, read this document： http://man7.org/linux/man-pages/man1/timeout.1.html

or you can use the param of ssh:

ssh -o ConnectTimeout=3 user@ip

edited Nov 6, 2015 at 14:24

answered Sep 4, 2015 at 4:10

Lee HoYo

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6 Comments

larcher Over a year ago

If you're looking for this command on a Mac, try brew install coreutils and then use gtimeout (source: stackoverflow.com/questions/3504945/timeout-command-on-mac-os-x ).

James Davis Over a year ago

This may not do what you want. Consider the command timeout 3s ssh user@server 'sleep 5; echo blarg >> /tmp/blarg' This kills the process on the SSH client side, but /tmp/blarg still gets modified on the remote server. This means that if you are running a runaway CPU-intensive job on the remote server, you will leak processes.

FilipR Over a year ago

@JamieDavis what about ssh user@server 'timeout 5s sleep 10' ?

xeruf Over a year ago

@FilipR this doesn't time out if the connection is never made ;)

Rich Over a year ago

"this ... or this" should normally raise the question "why not both?" A combination of both is what I use in my own scripting. The threshold for timeout $X should be larger than the that for ssh -o ConnectTimeout=$Y (i.e. X > Y), naturally. This catches the situation where the remote machine is hanging after the connection is successfully made and you never get to your next machine in the queue.

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javabrett · Accepted Answer · 2016-12-13 03:28:47Z

31

You could also connect with flag

-o ServerAliveInterval=<secs>

so the SSH client will send a null packet to the server each <secs> seconds, just to keep the connection alive. In Linux this could be also set globally in /etc/ssh/ssh_config or per-user in ~/.ssh/config.

edited Dec 13, 2016 at 3:28

javabrett

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answered Mar 16, 2015 at 8:40

Patrizio Bertoni

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1 Comment

Davor Cubranic Over a year ago

That sounds like the opposite of what the question requests.

Danie · Accepted Answer · 2024-10-25 05:40:09Z

10

just adding the following .ssh/config snippet that I use,

  ServerAliveInterval 20
  ServerAliveCountMax 5
  ConnectTimeout 10

ConnectTimeout Specifies the timeout (in seconds) used when connecting to the SSH server, instead of using the default system TCP timeout. This timeout is applied both to establishing the connection and to performing the initial SSH protocol handshake and key exchange. (from the doc)

edited Oct 25, 2024 at 5:40

answered Mar 28, 2023 at 11:30

Danie

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3 Comments

rkochar Over a year ago

Useful to add that the unit is seconds according to doc.

feyzullahyildiz Over a year ago

should I add these value into client's .ssh/config or in remote server's .ssh/config

Danie Over a year ago

to the user's client config that will use ssh to a remote server

Philip Kearns · Accepted Answer · 2019-05-20 14:32:12Z

4

If all else fails (including not having the timeout command) the concept in this shell script will work:

 #!/bin/bash
 set -u
 ssh $1 "sleep 10 ; uptime" > /tmp/outputfile 2>&1 & PIDssh=$!
 Count=0
 while test $Count -lt 5 && ps -p $PIDssh > /dev/null
 do
    echo -n .
    sleep 1
    Count=$((Count+1))
 done
 echo ""

 if ps -p $PIDssh > /dev/null
 then
    echo "ssh still running, killing it"
    kill -HUP $PIDssh
 else
    echo "Exited"
 fi

answered May 20, 2019 at 14:32

Philip Kearns

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Comments

Rob Bednark · Accepted Answer · 2024-05-16 19:01:44Z

2

timeout 5 ssh user@machine works for me.

edited May 16, 2024 at 19:01

Rob Bednark

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answered Jan 24, 2022 at 21:09

Hanish Madan

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Comments

Benjamin Loison · Accepted Answer · 2023-12-01 18:05:45Z

0

Well, you could use nohup to run whatever you are running on 'non-blocking mode'. So you can just keep checking if whatever it was supposed to run, ran, otherwise exit.

nohup ./my-script-that-may-take-long-to-finish.sh &
./check-if-previous-script-ran-or-exit.sh

echo "Script ended on Feb 15, 2011, 9:20AM" > /tmp/done.txt

So in the second one you just check if the file exists.

edited Dec 1, 2023 at 18:05

Benjamin Loison

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answered Feb 8, 2011 at 18:35

Eduardo

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2 Comments

user57421 Over a year ago

Makes sense. but, the script which is running gives me some output, which is displayed on the console.. how to check if my previous script ran or exit? $? or anything else ?

Eduardo Over a year ago

Well you could make that script create a file when done. I've added the comment to the answer.... grrr

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