I'm executing a bash script in Node.js like this:
const script = child_process.spawn('local_script.sh');
const stdout = fs.createWriteStream('stdout');
const stderr = fs.createWriteStream('stderr');
script.stdout.pipe(stdout);
script.stderr.pipe(stderr);
script.on('close', function(code) {
console.log('Script exited with code', code);
});
My local_script.sh uploads a script to my remote server and executes it:
#!/bin/bash
FILE=/root/remote_script.sh
HOST=123.456.78.9
scp remote_script.sh root#${HOST}:${FILE}
ssh root#${HOST} bash ${FILE}
Finally, my remote_script.sh is supposed to open an SSH tunnel (and perform some other actions that are not relevant for this question):
#!/bin/bash
REDIS_HOST=318.353.31.3
ssh -f -n root#${REDIS_HOST} -L 6379:127.0.0.1:6379 -N &
The problem is that even though I'm opening the SSH tunnel in the background, it seems my remote_script.sh never exits, because the Node.js close event is never called. If I don't open the SSH tunnel, it exits and emits the event as expected.
How can I make sure the script exits cleanly after opening the SSH tunnel? Note that I want the tunnel to persist after the script finishes.
I haven't tested this, but my guess is that the backgrounded ssh session (remote -> REDIS) is keeping the remote tty alive, and thus preventing the local -> remote session from closing. Try changing remote_script.sh to this:
#!/bin/bash
redis_host=318.353.31.3
nohup ssh -f -n "root#${redis_host}" -L 6379:127.0.0.1:6379 -N >/dev/null 2>&1 &
BTW, note that I switched the variable name to lowercase; there are a number of all-caps variables with special meanings (including HOST), and re-using any of them can have weird effects, so lower- or mixed-case variables are preferred for script use. Also, I double-quoted the variable reference, which won't matter in this case but is a good general habit for those cases where it does matter.
The way I managed to solve it is by using ssh -a root${HOST} bash ${FILE} in my local_script.sh. Note the -a flag which disables my forwarding ssh agent.
The important clue was that when I ran remote_script.sh on my remote machine directly, it would do everything as expected including a clean exit, but when I would try to logout, that's where it would hang.
Apparently ssh doesn't want to terminate while there are still active connections. When I typed ~#, which shows active ssh connections, it did indeed show my forwarding ssh agent.
What is a good way to be able to directly send to STDIN and receive from STDOUT of a process? I'm specifically interested in SSH, as I want to do the following:
[ssh into a remote server]
[run remote commands]
[run local commands]
[run remote commands]
etc...
For example, let's say I have a local script "localScript" that will output the next command I want to run remotely, depending on the output of "remoteScript". I could do something like:
output=$(ssh myServer "./remoteScript")
nextCommand=$(./localScript $output)
ssh myServer "$nextCommand"
But it would be nice to do this without closing/reopening the SSH connection at every step.
You can redirect SSH input and output to FIFO-s and then use these for two-way communication.
For example local.sh:
#!/bin/sh
SSH_SERVER="myServer"
# Redirect SSH input and output to temporary named pipes (FIFOs)
SSH_IN=$(mktemp -u)
SSH_OUT=$(mktemp -u)
mkfifo "$SSH_IN" "$SSH_OUT"
ssh "$SSH_SERVER" "./remote.sh" < "$SSH_IN" > "$SSH_OUT" &
# Open the FIFO-s and clean up the files
exec 3>"$SSH_IN"
exec 4<"$SSH_OUT"
rm -f "$SSH_IN" "$SSH_OUT"
# Read and write
counter=0
echo "PING${counter}" >&3
cat <&4 | while read line; do
echo "Remote responded: $line"
sleep 1
counter=$((counter+1))
echo "PING${counter}" >&3
done
And simple remote.sh:
#!/bin/sh
while read line; do
echo "$line PONG"
done
The method you are using works, but I don't think you can reuse the same connection everytime. You can, however, do this using screen, tmux or nohup, but that would greatly increase the complexity of your script because you will now have to emulate keypresses/shortcuts. I'm not even sure if you can if you do directly in bash. If you want to emulate keypresses, you will have to run the script in a new x-terminal and use xdotool to emulate the keypresses.
Another method is to delegate the whole script to the SSH server by just running the script on the remote server itself:
ssh root#MachineB 'bash -s' < local_script.sh
I'm trying to have a shell script I can use to do connect somemachine to simplify the following pattern
ssh somemachine
tmux a
I've tried using here docs as Python subprocess with heredocs in order to send "tmux a" command
#!/bin/bash
ssh $1#$2 << 'ENDSSH'
tmux a
ENDSSH
however that fails with "stdin is not a terminal". Following suggestion in Pseudo-terminal will not be allocated because stdin is not a terminal I did following modification
#!/bin/bash
ssh -tt $1#$2 << 'ENDSSH'
tmux a
ENDSSH
But now all my shortcuts are intercepted. IE, CTRL+C will kill my SSH session rather than forwarding SIGINT to the process. Any suggestions?
I think you just need the -t flag and not use the heredoc. Using the heredoc means that the ssh process doesn't have the terminal as its stdin (it has the heredoc instead) so it can't forward it to pseudo-terminal on the remote side. Using the -tt flag forces the pts to be allocated without having an input which means that keypresses go to the local process not the remote one.
#!/bin/bash
ssh $1#$2 -t tmux a
works for me
I am using SSH to start a background process on a remote server. This is what I have at the moment:
ssh remote_user#server.com "nohup process &"
This works, in that the process does start. But the SSH session itself does not end until I hit Ctr-C.
When I hit Ctr-C, the remote process continues to run in the background.
I would like to place the ssh command in a script that I can run locally, so I would like the ssh session to exit automatically once the remote process has started.
Is there a way to make this happen?
The "-f" option to ssh tells ssh to run the remote command in the background and to return immediately. E.g.,
ssh -f user#host "echo foo; sleep 5; echo bar"
If you type the above, you will get your shell prompt back immediately, you will then see "foo" output. Five seconds later you will then see "bar" output. In the meantime, you could have been using the shell.
When using nohup, make sure you also redirect stdin, stdout and stderr:
ssh user#server 'DISPLAY=:0 nohup xeyes < /dev/null > std.out 2> std.err &'
In this way you will be completely detached from the remote process. Be carefull with using ssh -f user#host... since that will only put the ssh process in the background on the calling side. You can verify this by running a ps -aux | grep ssh on the calling machine and this will show you that the ssh call is still active, but just put in the background.
In my example above I use DISPLAY=:0 since xeyes is an X11 program and I want it started on the remote machine.
You could use screen to run your process on this screen, detach from screen Ctrl-a :detach and exit your current session without problem. Then you can reconnect to SSH and attach to this screen again to continue with your task or check if is finished.
Or you can send the command to an already running screen. Your local script should look like this:
ssh remote_user#server.com
screen -dmS new_screen sh
screen -S new_screen -p 0 -X stuff $'nohup process \n'
exit
For more info see this tutorial
Well this question is almost 10 years old, but I recently had to launch a very long script (taking several hours to complete) on a remote server and I found a way using the crontab.
If can edit your user's crontab on the remote server, connect with ssh to the server, edit the crontab and add an entry that will start your script the next minute. Let's say it's 15h03. Add this line :
4 15 * * * /path/to/your/script.sh
save your crontab, wait a minute for the script to be launched. Then edit again your crontab to remove this entry.
You can then safely exit ssh, even shut down your computer while the script is running.
I am trying to write a shell script that creates some directories on a remote server and then uses scp to copy files from my local machine onto the remote. Here's what I have so far:
ssh -t user#server<<EOT
DEP_ROOT='/home/matthewr/releases'
datestamp=$(date +%Y%m%d%H%M%S)
REL_DIR=$DEP_ROOT"/"$datestamp
if [ ! -d "$DEP_ROOT" ]; then
echo "creating the root directory"
mkdir $DEP_ROOT
fi
mkdir $REL_DIR
exit
EOT
scp ./dir1 user#server:$REL_DIR
scp ./dir2 user#server:$REL_DIR
Whenever I run it I get this message:
Pseudo-terminal will not be allocated because stdin is not a terminal.
And the script just hangs forever.
My public key is trusted on the server and I can run all the commands outside of the script just fine. Any ideas?
Try ssh -t -t(or ssh -tt for short) to force pseudo-tty allocation even if stdin isn't a terminal.
See also: Terminating SSH session executed by bash script
From ssh manpage:
-T Disable pseudo-tty allocation.
-t Force pseudo-tty allocation. This can be used to execute arbitrary
screen-based programs on a remote machine, which can be very useful,
e.g. when implementing menu services. Multiple -t options force tty
allocation, even if ssh has no local tty.
Also with option -T from manual
Disable pseudo-tty allocation
Per zanco's answer, you're not providing a remote command to ssh, given how the shell parses the command line. To solve this problem, change the syntax of your ssh command invocation so that the remote command is comprised of a syntactically correct, multi-line string.
There are a variety of syntaxes that can be used. For example, since commands can be piped into bash and sh, and probably other shells too, the simplest solution is to just combine ssh shell invocation with heredocs:
ssh user#server /bin/bash <<'EOT'
echo "These commands will be run on: $( uname -a )"
echo "They are executed by: $( whoami )"
EOT
Note that executing the above without /bin/bash will result in the warning Pseudo-terminal will not be allocated because stdin is not a terminal. Also note that EOT is surrounded by single-quotes, so that bash recognizes the heredoc as a nowdoc, turning off local variable interpolation so that the command text will be passed as-is to ssh.
If you are a fan of pipes, you can rewrite the above as follows:
cat <<'EOT' | ssh user#server /bin/bash
echo "These commands will be run on: $( uname -a )"
echo "They are executed by: $( whoami )"
EOT
The same caveat about /bin/bash applies to the above.
Another valid approach is to pass the multi-line remote command as a single string, using multiple layers of bash variable interpolation as follows:
ssh user#server "$( cat <<'EOT'
echo "These commands will be run on: $( uname -a )"
echo "They are executed by: $( whoami )"
EOT
)"
The solution above fixes this problem in the following manner:
ssh user#server is parsed by bash, and is interpreted to be the ssh command, followed by an argument user#server to be passed to the ssh command
" begins an interpolated string, which when completed, will comprise an argument to be passed to the ssh command, which in this case will be interpreted by ssh to be the remote command to execute as user#server
$( begins a command to be executed, with the output being captured by the surrounding interpolated string
cat is a command to output the contents of whatever file follows. The output of cat will be passed back into the capturing interpolated string
<< begins a bash heredoc
'EOT' specifies that the name of the heredoc is EOT. The single quotes ' surrounding EOT specifies that the heredoc should be parsed as a nowdoc, which is a special form of heredoc in which the contents do not get interpolated by bash, but rather passed on in literal format
Any content that is encountered between <<'EOT' and <newline>EOT<newline> will be appended to the nowdoc output
EOT terminates the nowdoc, resulting in a nowdoc temporary file being created and passed back to the calling cat command. cat outputs the nowdoc and passes the output back to the capturing interpolated string
) concludes the command to be executed
" concludes the capturing interpolated string. The contents of the interpolated string will be passed back to ssh as a single command line argument, which ssh will interpret as the remote command to execute as user#server
If you need to avoid using external tools like cat, and don't mind having two statements instead of one, use the read built-in with a heredoc to generate the SSH command:
IFS='' read -r -d '' SSH_COMMAND <<'EOT'
echo "These commands will be run on: $( uname -a )"
echo "They are executed by: $( whoami )"
EOT
ssh user#server "${SSH_COMMAND}"
I'm adding this answer because it solved a related problem that I was having with the same error message.
Problem: I had installed cygwin under Windows and was getting this error: Pseudo-terminal will not be allocated because stdin is not a terminal
Resolution: It turns out that I had not installed the openssh client program and utilities. Because of that cygwin was using the Windows implementation of ssh, not the cygwin version. The solution was to install the openssh cygwin package.
All relevant information is in the existing answers, but let me attempt a pragmatic summary:
tl;dr:
DO pass the commands to run using a command-line argument:
ssh jdoe#server '...'
'...' strings can span multiple lines, so you can keep your code readable even without the use of a here-document:
ssh jdoe#server ' ... '
Do NOT pass the commands via stdin, as is the case when you use a here-document:
ssh jdoe#server <<'EOF' # Do NOT do this ... EOF
Passing the commands as an argument works as-is, and:
the problem with the pseudo-terminal will not even arise.
you won't need an exit statement at the end of your commands, because the session will automatically exit after the commands have been processed.
In short: passing commands via stdin is a mechanism that is at odds with ssh's design and causes problems that must then be worked around.
Read on, if you want to know more.
Optional background information:
ssh's mechanism for accepting commands to execute on the target server is a command-line argument: the final operand (non-option argument) accepts a string containing one or more shell commands.
By default, these commands run unattended, in a non-interactive shell, without the use of a (pseudo) terminal (option -T is implied), and the session automatically ends when the last command finishes processing.
In the event that your commands require user interaction, such as responding to an interactive prompt, you can explicitly request the creation of a pty (pseudo-tty), a pseudo terminal, that enables interacting with the remote session, using the -t option; e.g.:
ssh -t jdoe#server 'read -p "Enter something: "; echo "Entered: [$REPLY]"'
Note that the interactive read prompt only works correctly with a pty, so the -t option is needed.
Using a pty has a notable side effect: stdout and stderr are combined and both reported via stdout; in other words: you lose the distinction between regular and error output; e.g.:
ssh jdoe#server 'echo out; echo err >&2' # OK - stdout and stderr separate
ssh -t jdoe#server 'echo out; echo err >&2' # !! stdout + stderr -> stdout
In the absence of this argument, ssh creates an interactive shell - including when you send commands via stdin, which is where the trouble begins:
For an interactive shell, ssh normally allocates a pty (pseudo-terminal) by default, except if its stdin is not connected to a (real) terminal.
Sending commands via stdin means that ssh's stdin is no longer connected to a terminal, so no pty is created, and ssh warns you accordingly:
Pseudo-terminal will not be allocated because stdin is not a terminal.
Even the -t option, whose express purpose is to request creation of a pty, is not enough in this case: you'll get the same warning.
Somewhat curiously, you must then double the -t option to force creation of a pty: ssh -t -t ... or ssh -tt ... shows that you really, really mean it.
Perhaps the rationale for requiring this very deliberate step is that things may not work as expected. For instance, on macOS 10.12, the apparent equivalent of the above command, providing the commands via stdin and using -tt, does not work properly; the session gets stuck after responding to the read prompt:
ssh -tt jdoe#server <<<'read -p "Enter something: "; echo "Entered: [$REPLY]"'
In the unlikely event that the commands you want to pass as an argument make the command line too long for your system (if its length approaches getconf ARG_MAX - see this article), consider copying the code to the remote system in the form of a script first (using, e.g., scp), and then send a command to execute that script.
In a pinch, use -T, and provide the commands via stdin, with a trailing exit command, but note that if you also need interactive features, using -tt in lieu of -T may not work.
The warning message Pseudo-terminal will not be allocated because stdin is not a terminal. is due to the fact that no command is specified for ssh while stdin is redirected from a here document.
Due to the lack of a specified command as an argument ssh first expects an interactive login session (which would require the allocation of a pty on the remote host) but then has to realize that its local stdin is no tty/pty. Redirecting ssh's stdin from a here document normally requires a command (such as /bin/sh) to be specified as an argument to ssh - and in such a case no pty will be allocated on the remote host by default.
Since there are no commands to be executed via ssh that require the presence of a tty/pty (such as vim or top) the -t switch to ssh is superfluous.
Just use ssh -T user#server <<EOT ... or ssh user#server /bin/bash <<EOT ... and the warning will go away.
If <<EOF is not escaped or single-quoted (i. e. <<\EOT or <<'EOT') variables inside the here document will be expanded by the local shell before it is executing ssh .... The effect is that the variables inside the here document will remain empty because they are defined only in the remote shell.
So, if $REL_DIR should be both accessible by the local shell and defined in the remote shell, $REL_DIR has to be defined outside the here document before the ssh command (version 1 below); or, if <<\EOT or <<'EOT' is used, the output of the ssh command can be assigned to REL_DIR if the only output of the ssh command to stdout is genererated by echo "$REL_DIR" inside the escaped/single-quoted here document (version 2 below).
A third option would be to store the here document in a variable and then pass this variable as a command argument to ssh -t user#server "$heredoc" (version 3 below).
And, last but not least, it would be no bad idea to check if the directories on the remote host were created successfully (see: check if file exists on remote host with ssh).
# version 1
unset DEP_ROOT REL_DIR
DEP_ROOT='/tmp'
datestamp=$(date +%Y%m%d%H%M%S)
REL_DIR="${DEP_ROOT}/${datestamp}"
ssh localhost /bin/bash <<EOF
if [ ! -d "$DEP_ROOT" ] && [ ! -e "$DEP_ROOT" ]; then
echo "creating the root directory" 1>&2
mkdir "$DEP_ROOT"
fi
mkdir "$REL_DIR"
#echo "$REL_DIR"
exit
EOF
scp -r ./dir1 user#server:"$REL_DIR"
scp -r ./dir2 user#server:"$REL_DIR"
# version 2
REL_DIR="$(
ssh localhost /bin/bash <<\EOF
DEP_ROOT='/tmp'
datestamp=$(date +%Y%m%d%H%M%S)
REL_DIR="${DEP_ROOT}/${datestamp}"
if [ ! -d "$DEP_ROOT" ] && [ ! -e "$DEP_ROOT" ]; then
echo "creating the root directory" 1>&2
mkdir "$DEP_ROOT"
fi
mkdir "$REL_DIR"
echo "$REL_DIR"
exit
EOF
)"
scp -r ./dir1 user#server:"$REL_DIR"
scp -r ./dir2 user#server:"$REL_DIR"
# version 3
heredoc="$(cat <<'EOF'
# -onlcr: prevent the terminal from converting bare line feeds to carriage return/line feed pairs
stty -echo -onlcr
DEP_ROOT='/tmp'
datestamp="$(date +%Y%m%d%H%M%S)"
REL_DIR="${DEP_ROOT}/${datestamp}"
if [ ! -d "$DEP_ROOT" ] && [ ! -e "$DEP_ROOT" ]; then
echo "creating the root directory" 1>&2
mkdir "$DEP_ROOT"
fi
mkdir "$REL_DIR"
echo "$REL_DIR"
stty echo onlcr
exit
EOF
)"
REL_DIR="$(ssh -t localhost "$heredoc")"
scp -r ./dir1 user#server:"$REL_DIR"
scp -r ./dir2 user#server:"$REL_DIR"
I don't know where the hang comes from, but redirecting (or piping) commands into an interactive ssh is in general a recipe for problems. It is more robust to use the command-to-run-as-a-last-argument style and pass the script on the ssh command line:
ssh user#server 'DEP_ROOT="/home/matthewr/releases"
datestamp=$(date +%Y%m%d%H%M%S)
REL_DIR=$DEP_ROOT"/"$datestamp
if [ ! -d "$DEP_ROOT" ]; then
echo "creating the root directory"
mkdir $DEP_ROOT
fi
mkdir $REL_DIR'
(All in one giant '-delimited multiline command-line argument).
The pseudo-terminal message is because of your -t which asks ssh to try to make the environment it runs on the remote machine look like an actual terminal to the programs that run there. Your ssh client is refusing to do that because its own standard input is not a terminal, so it has no way to pass the special terminal APIs onwards from the remote machine to your actual terminal at the local end.
What were you trying to achieve with -t anyway?
After reading a lot of these answers I thought I would share my resulting solution. All I added is /bin/bash before the heredoc and it doesn't give the error anymore.
Use this:
ssh user#machine /bin/bash <<'ENDSSH'
hostname
ENDSSH
Instead of this (gives error):
ssh user#machine <<'ENDSSH'
hostname
ENDSSH
Or use this:
ssh user#machine /bin/bash < run-command.sh
Instead of this (gives error):
ssh user#machine < run-command.sh
EXTRA:
If you still want a remote interactive prompt e.g. if the script you're running remotely prompts you for a password or other information, because the previous solutions won't allow you to type into the prompts.
ssh -t user#machine "$(<run-command.sh)"
And if you also want to log the entire session in a file logfile.log:
ssh -t user#machine "$(<run-command.sh)" | tee -a logfile.log
I was having the same error under Windows using emacs 24.5.1 to connect to some company servers through /ssh:user#host. What solved my problem was setting the "tramp-default-method" variable to "plink" and whenever I connect to a server I ommit the ssh protocol. You need to have PuTTY's plink.exe installed for this to work.
Solution
M-x customize-variable (and then hit Enter)
tramp-default-method (and then hit Enter again)
On the text field put plink and then Apply and Save the buffer
Whenever I try to access a remote server I now use C-x-f /user#host: and then input the password. The connection is now correctly made under Emacs on Windows to my remote server.