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When I ssh to a remote host, Is it possible that I get the remote bash pid in my local machine? or vice versa?

for example on local terminal, I simply do ssh and keep connection to run my tasks:

ssh user@remote.com

and the ps is like this on local machine:

ps faux
...
shunh    32683  0.1  0.0 121148  5116 pts/2    Ss   07:02   0:00  \_ -bash
shunh    33079  0.6  0.0 189360  8484 pts/2    S+   07:03   0:00      \_ ssh -X remote_host

and on remote_host:

ps faux
...
root     214679  0.0  0.0 158820  5724 ?        Ss   07:03   0:00  \_ sshd: shunh [priv]
shunh    214681  0.0  0.0 158820  2556 ?        S    07:03   0:00      \_ sshd: shunh@pts/1
shunh    214682  0.0  0.0 121124  3608 pts/1    Ss   07:03   0:00          \_ -bash

So can I get the pid number "214682" in my local machine?

donkey1120
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  • The question is very strange. A direct, exact and completely useless answer would be: "ssh remote.system echo \$\$", which will print on local stdout a pid that bash had when it started on connection. That bash is immediately exited. But, why you want that pid? What do you want to achieve? – Nikita Kipriyanov Sep 24 '19 at 06:03

1 Answers1

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Simply

As @Nikita Kipriyanov commented, the simple way is

ssh user@remote.domain 'echo $$'

(using single quotes!), But seem not really usefull, because localhost will be able of reading process number only after they finish.

Use case:

There is some way of running ssh in order to foward ports, for sample: this will connect indirRem.remDom:22 via ssh proxy: user@rem.dom.

ssh -f -L2022:indirRem.remDom:22 user@rem.dom 'echo $$ $PPID;sleep 2' >/tmp/rpids.txt &&
    ssh -o HostKeyAlias=indirectRemote.remotedomain -p 2022 indUser@localhost

From there, if on localhost, you hit something like:

ssh user@rem.dom ps ef $(</tmp/rpids.txt)

You may see wich pid is used for current (open) session (while you don't close/end shell session on indirRem.remDom:22).

Mariadb/Mysql sample:

ssh -f -L 3306:localhost:3306 user@rem.dom 'echo $$ $PPID;sleep 2' >/tmp/rpids.txt &&
    mariadb -h 127.0.0.1 -p"What a strong password" database

This will locally run mariadb client on local 3306 tcp port, but this port is a forwarded port from rem.dom (wich is normally listenning on loopback device only)

Same but forwarding UNIX socket instead of TCP service:

ssh -f -L 3306:/var/run/mysqld/mysqld.sock user@rem.dom 'echo $$ $PPID;sleep 2' >/tmp/rpids.txt &&
    mariadb -h 127.0.0.1 -p"What a strong password" database

Then

ssh user@rem.dom ps ef $(</tmp/rpids.txt)

will show the sshd process who hold forwarded ports.

But

Anyway, I don't see what to do with this /tmp/rpids.txt.

Read man ssh and man sshd, look for -M (master) and -S (slave) switches.

F. Hauri - Give Up GitHub
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