I send a tee command from host 1 to host 2:
ssh user#host2 '/path/run |& tee myFile.txt'
I use tee so that I get the output of the binary to be added to myFile.txt
The problem I have then is after a bit of time, I want to regain control of my local host without having a lot of printout. So I do CTRL+C. This lets the process on host2 continue to run, which is what I want, but it stops the tee process itself, so the file is not populated.
I tried to replace |& tee myFile.txt' by 2>&1 myFile.txt' & but it did not help.
How can I ensure that the file continues to be populated on host2, while regaining control to my session on host1?
If you want to record the results in some file (work with IO redirection inside of the nohup), you need to enclose all the pipeline in the nohup. It does not use shell expansions, since argument is only COMMAND ARGS, so using a sh is a good way:
ssh user#host2 'nohup sh -c "/path/run |& tee myFile.txt" &'
but note that nohup will disconnect the terminal from the command ant it might fail. Useful would be to redirect it directly to the file:
ssh user#host2 'nohup sh -c "/path/run &> myFile.txt" &'
Inspiration from the SO answer.
use nohup, screen or tmux for backgrounding a process.
I have this script:
#!/bin/sh
while [ true ] ; do
urlfile=$( ls /root/wget/wget-download-link.txt | head -n 1 )
dir=$( cat /root/wget/wget-dir.txt )
if [ "$urlfile" = "" ] ; then
sleep 30
continue
fi
url=$( head -n 1 $urlfile )
if [ "$url" = "" ] ; then
mv $urlfile $urlfile.invalid
continue
fi
mv $urlfile $urlfile.busy
wget -b $url -P $dir -o /www/wget.log -c -t 100 -nc
mv $urlfile.busy $urlfile.done
done
The script basically checks for any new URLs at wget-download-link.txt for every 30 seconds and if there's a new URL it'll download it with wget, the problem is that when I try to run this script on Putty like this
/root/wget/wget_download.sh --daemon
it's still running in the foreground, I still can see the terminal output. How do I make it run in the background ?
In OpenWRT there is neither nohup nor screen available by default, so a solution with only builtin commands would be to start a subshell with brackets and put that one in the background with &:
(/root/wget/wget_download.sh >/dev/null 2>&1 )&
you can test this structure easily on your desktop for example with
(notify-send one && sleep 15 && notify-send two)&
... and then close your console before those 15 seconds are over, you will see the commands in the brackets continue execution after closing the console.
The following command will also work:
((/root/wget/wget_download.sh)&)&
This way you don't have to install the 'nohub' command in the tight memory space of the router used for OpenWrt.
I found this somewhere several years ago. It works.
The &at the end of script should be enough, if you see output from the script it means, that stdout and/or stderr is not closed, or not redirect to /dev/null
You can use this answer:
How to redirect all output to /dev/null
I am using openwrt merlin and the only way to get it working was using the crud cron manager[1]. Nohub and screen are not available as solutions.
cru a pinggw "0 * * * * /bin/ping -c 10 -q 192.168.2.254"
works like charm
[1][https://www.cyberciti.biz/faq/how-to-add-cron-job-on-asuswrt-merlin-wifi-router/]
https://openwrt.org/packages/pkgdata/coreutils-nohup
opkg update
opkg install coreutils-nohup
nohup yourscript.sh &
You can use nohup.
nohup yourscript.sh
or
nohup yourscript.sh &
Your script will keep running even if you close your putty session, and all the output will be written to a text file in same directory.
nohup is often used in combination with the nice command to run processes on a lower priority.
nohup nice yourscript.sh &
See: http://en.wikipedia.org/wiki/Nohup
For busybox in Openwrt Merlin system, I got a better solution which combined cru and date command
cru a YOUR_UNIQUE_CRON_NAME "`date -D '%s' +'%M %H %d %m *' -d $(( \`date +%s\`+2*60 ))` YOUR_CMD_HERE"
which add a cron job running 2 minutes later, and only run once.
Inspired by PlagTag's idea.
In another way these code would tried:
ssh admin#192.168.1.1 "/jffs/your_script.sh &"
Simple and without any programs like nohup screen...
(BTW: worked on Asus-Merlin firmware)
Try this:
nohup /root/wget/wget_download.sh >/dev/null 2>&1 &
It will go to the background so when you close your Putty session, it will be still running, and it won't send messages to the terminal.
If I run a process at the remote site by using ssh as follows:
nohup ssh remote sleep 100 &
Is there a way to know the PID of sleep at remote?
Trying echo $! just returns the PID of ssh at local.
And, greping won't work since there are multiple sleep processes at remote.
You could pass a string to ssh so try
nohup ssh remote 'sleep 100 &; echo $!'
Try the following
nohup ssh remote 'sleep 100 > out 2> err < /dev/null & echo $!'
This is a follow-on question to the How do you use ssh in a shell script? question. If I want to execute a command on the remote machine that runs in the background on that machine, how do I get the ssh command to return? When I try to just include the ampersand (&) at the end of the command it just hangs. The exact form of the command looks like this:
ssh user#target "cd /some/directory; program-to-execute &"
Any ideas? One thing to note is that logins to the target machine always produce a text banner and I have SSH keys set up so no password is required.
I had this problem in a program I wrote a year ago -- turns out the answer is rather complicated. You'll need to use nohup as well as output redirection, as explained in the wikipedia artcle on nohup, copied here for your convenience.
Nohuping backgrounded jobs is for
example useful when logged in via SSH,
since backgrounded jobs can cause the
shell to hang on logout due to a race
condition [2]. This problem can also
be overcome by redirecting all three
I/O streams:
nohup myprogram > foo.out 2> foo.err < /dev/null &
This has been the cleanest way to do it for me:-
ssh -n -f user#host "sh -c 'cd /whereever; nohup ./whatever > /dev/null 2>&1 &'"
The only thing running after this is the actual command on the remote machine
Redirect fd's
Output needs to be redirected with &>/dev/null which redirects both stderr and stdout to /dev/null and is a synonym of >/dev/null 2>/dev/null or >/dev/null 2>&1.
Parantheses
The best way is to use sh -c '( ( command ) & )' where command is anything.
ssh askapache 'sh -c "( ( nohup chown -R ask:ask /www/askapache.com &>/dev/null ) & )"'
Nohup Shell
You can also use nohup directly to launch the shell:
ssh askapache 'nohup sh -c "( ( chown -R ask:ask /www/askapache.com &>/dev/null ) & )"'
Nice Launch
Another trick is to use nice to launch the command/shell:
ssh askapache 'nice -n 19 sh -c "( ( nohup chown -R ask:ask /www/askapache.com &>/dev/null ) & )"'
If you don't/can't keep the connection open you could use screen, if you have the rights to install it.
user#localhost $ screen -t remote-command
user#localhost $ ssh user#target # now inside of a screen session
user#remotehost $ cd /some/directory; program-to-execute &
To detach the screen session: ctrl-a d
To list screen sessions:
screen -ls
To reattach a session:
screen -d -r remote-command
Note that screen can also create multiple shells within each session. A similar effect can be achieved with tmux.
user#localhost $ tmux
user#localhost $ ssh user#target # now inside of a tmux session
user#remotehost $ cd /some/directory; program-to-execute &
To detach the tmux session: ctrl-b d
To list screen sessions:
tmux list-sessions
To reattach a session:
tmux attach <session number>
The default tmux control key, 'ctrl-b', is somewhat difficult to use but there are several example tmux configs that ship with tmux that you can try.
I just wanted to show a working example that you can cut and paste:
ssh REMOTE "sh -c \"(nohup sleep 30; touch nohup-exit) > /dev/null &\""
You can do this without nohup:
ssh user#host 'myprogram >out.log 2>err.log &'
Quickest and easiest way is to use the 'at' command:
ssh user#target "at now -f /home/foo.sh"
I think you'll have to combine a couple of these answers to get what you want. If you use nohup in conjunction with the semicolon, and wrap the whole thing in quotes, then you get:
ssh user#target "cd /some/directory; nohup myprogram > foo.out 2> foo.err < /dev/null"
which seems to work for me. With nohup, you don't need to append the & to the command to be run. Also, if you don't need to read any of the output of the command, you can use
ssh user#target "cd /some/directory; nohup myprogram > /dev/null 2>&1"
to redirect all output to /dev/null.
This worked for me may times:
ssh -x remoteServer "cd yourRemoteDir; ./yourRemoteScript.sh </dev/null >/dev/null 2>&1 & "
You can do it like this...
sudo /home/script.sh -opt1 > /tmp/script.out &
It appeared quite convenient for me to have a remote tmux session using the tmux new -d <shell cmd> syntax like this:
ssh someone#elsewhere 'tmux new -d sleep 600'
This will launch new session on elsewhere host and ssh command on local machine will return to shell almost instantly. You can then ssh to the remote host and tmux attach to that session. Note that there's nothing about local tmux running, only remote!
Also, if you want your session to persist after the job is done, simply add a shell launcher after your command, but don't forget to enclose in quotes:
ssh someone#elsewhere 'tmux new -d "~/myscript.sh; bash"'
Actually, whenever I need to run a command on a remote machine that's complicated, I like to put the command in a script on the destination machine, and just run that script using ssh.
For example:
# simple_script.sh (located on remote server)
#!/bin/bash
cat /var/log/messages | grep <some value> | awk -F " " '{print $8}'
And then I just run this command on the source machine:
ssh user#ip "/path/to/simple_script.sh"
If you run remote command without allocating tty, redirect stdout/stderr works, nohup is not necessary.
ssh user#host 'background command &>/dev/null &'
If you use -t to allocate tty to run interactive command along with background command, and background command is the last command, like this:
ssh -t user#host 'bash -c "interactive command; nohup backgroud command &>/dev/null &"'
It's possible that background command doesn't actually start. There's race here:
bash exits after nohup starts. As a session leader, bash exit results in HUP signal sent to nohup process.
nohup ignores HUP signal.
If 1 completes before 2, the nohup process will exit and won't start the background command at all. We need to wait nohup start the background command. A simple workaroung is to just add a sleep:
ssh -t user#host 'bash -c "interactive command; nohup backgroud command &>/dev/null & sleep 1"'
The question was asked and answered years ago, I don't know if openssh behavior changed since then. I was testing on:
OpenSSH_8.6p1, OpenSSL 1.1.1g FIPS 21 Apr 2020
I was trying to do the same thing, but with the added complexity that I was trying to do it from Java. So on one machine running java, I was trying to run a script on another machine, in the background (with nohup).
From the command line, here is what worked: (you may not need the "-i keyFile" if you don't need it to ssh to the host)
ssh -i keyFile user#host bash -c "\"nohup ./script arg1 arg2 > output.txt 2>&1 &\""
Note that to my command line, there is one argument after the "-c", which is all in quotes. But for it to work on the other end, it still needs the quotes, so I had to put escaped quotes within it.
From java, here is what worked:
ProcessBuilder b = new ProcessBuilder("ssh", "-i", "keyFile", "bash", "-c",
"\"nohup ./script arg1 arg2 > output.txt 2>&1 &\"");
Process process = b.start();
// then read from process.getInputStream() and close it.
It took a bit of trial & error to get this working, but it seems to work well now.
YOUR-COMMAND &> YOUR-LOG.log &
This should run the command and assign a process id you can simply tail -f YOUR-LOG.log to see results written to it as they happen. you can log out anytime and the process will carry on
If you are using zsh then use program-to-execute &! is a zsh-specific shortcut to both background and disown the process, such that exiting the shell will leave it running.
A follow-on to #cmcginty's concise working example which also shows how to alternatively wrap the outer command in double quotes. This is how the template would look if invoked from within a PowerShell script (which can only interpolate variables from within double-quotes and ignores any variable expansion when wrapped in single quotes):
ssh user#server "sh -c `"($cmd) &>/dev/null </dev/null &`""
Inner double-quotes are escaped with back-tick instead of backslash. This allows $cmd to be composed by the PowerShell script, e.g. for deployment scripts and automation and the like. $cmd can even contain a multi-line heredoc if composed with unix LF.
First follow this procedure:
Log in on A as user a and generate a pair of authentication keys. Do not enter a passphrase:
a#A:~> ssh-keygen -t rsa
Generating public/private rsa key pair.
Enter file in which to save the key (/home/a/.ssh/id_rsa):
Created directory '/home/a/.ssh'.
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /home/a/.ssh/id_rsa.
Your public key has been saved in /home/a/.ssh/id_rsa.pub.
The key fingerprint is:
3e:4f:05:79:3a:9f:96:7c:3b:ad:e9:58:37:bc:37:e4 a#A
Now use ssh to create a directory ~/.ssh as user b on B. (The directory may already exist, which is fine):
a#A:~> ssh b#B mkdir -p .ssh
b#B's password:
Finally append a's new public key to b#B:.ssh/authorized_keys and enter b's password one last time:
a#A:~> cat .ssh/id_rsa.pub | ssh b#B 'cat >> .ssh/authorized_keys'
b#B's password:
From now on you can log into B as b from A as a without password:
a#A:~> ssh b#B
then this will work without entering a password
ssh b#B "cd /some/directory; program-to-execute &"
I think this is what you need:
At first you need to install sshpass on your machine.
then you can write your own script:
while read pass port user ip; do
sshpass -p$pass ssh -p $port $user#$ip <<ENDSSH1
COMMAND 1
.
.
.
COMMAND n
ENDSSH1
done <<____HERE
PASS PORT USER IP
. . . .
. . . .
. . . .
PASS PORT USER IP
____HERE
On Linux system, how does one run a process as a different, unprivileged user (like how lighttpd is run by www-data in the default setup)?
I've been using su $user; $command & over ssh, but those processes get killed when I logout.
If it makes any difference, I'm using a default Ubuntu setup on EC2.
su $other_user -c 'nohup sleep 600 &'
nohup $command </dev/null >/dev/null 2>/dev/null &
or
command </dev/null >/dev/null 2>/dev/null &; disown