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How to remotely execute a system command on a remote shell

P: 6
Hi
I am trying to execute a system command in my "C" code running on a Ubuntu Linux machine. The code is supposed to open a secure shell connection to another machine, change directories to a given directory and run an executable on that machine. I have configured the remote machine through ssh keygen to be able to authenticate my account and bypass the password. here is my "C" code:


void create_server(char *servermcnm)
{
char command1[100] = "ssh -X ";
strcat(command1,servermcnm);
strcat(command1," &");
char command2[100] = "cd ~/P1/P1*";
system(command1);
system(command2);
system("./server &");
}

In the above code, servermcnm is the name of the remote machine. The system(command1) call works, because I am able to reach a terminal session on the other machine, but I want the system(command2) line and system("./server &) to execute on the remote machine, but it doesn't work.
Dec 21 '06 #1
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6 Replies


sashi
Expert 100+
P: 1,754
Hi
I am trying to execute a system command in my "C" code running on a Ubuntu Linux machine. The code is supposed to open a secure shell connection to another machine, change directories to a given directory and run an executable on that machine. I have configured the remote machine through ssh keygen to be able to authenticate my account and bypass the password. here is my "C" code:


void create_server(char *servermcnm)
{
char command1[100] = "ssh -X ";
strcat(command1,servermcnm);
strcat(command1," &");
char command2[100] = "cd ~/P1/P1*";
system(command1);
system(command2);
system("./server &");
}

In the above code, servermcnm is the name of the remote machine. The system(command1) call works, because I am able to reach a terminal session on the other machine, but I want the system(command2) line and system("./server &) to execute on the remote machine, but it doesn't work.
Hi there,

Have you assigned execute permission to the script? Please check this detail. Good luck & Take care.
Dec 21 '06 #2

P: 6
I have assigned execute permission to the script. The problem is that because I am actually trying to run an executable with my C program embedded code, I am able to run the first command ("namely ssh -X servermcnm"), from my program, but then the subsequent commands to change directory and run the executable aren't running for some reason. The error I receive is something like "can't open a pseudo-terminal session because stdin is not blah blah blah".

Once I reach the other machine by executing the ssh command in my code, the next line in my code needs to be executed on the remote machine's shell, but for whatever reason it fails. I am not sure if this is a configuration related issue or something else. Here's the code:

void create_server(char *servermcnm)
{
char command1[100] = "ssh -X ";
strcat(command1,servermcnm);
strcat(command1," &");
char command2[100] = "cd ~/P1/P1*";
system(command1);
system(command2);
system("./server &");
}
Dec 21 '06 #3

Expert 100+
P: 534
This may not be the whole story, but I think there's at least one problem with your code:

You make one "system" call to change directory.
Then you call system again to do something else.
Are your making an assumption that you're still in that directory?

try this (pseudocode)
Expand|Select|Wrap|Line Numbers
  1. system ("cd /home/users/me/subdir/");
  2. system("touch ABCDEF");
  3.  
I expect file ABCDEF will be created wherever you execute your program, not necesarily in /home/users/me/subdir/

What happens if you chain all your commands with ";" and call system just once?
Dec 21 '06 #4

P: 6
I tried the suggestion made on the previous reply about chaining commands together with ";" and making one system call, but I receive a run time error stating that ";" wasn't recognized.

I am not sure how to get around this problem, but I need to run my "server" program in machine b from calling it with C language code in machine A. I know I need to ssh into machine b, but I don't know how to run the server program in machine b with my C language code right after "ssh"ing into the machine b. Any suggestions about "C" code utilizing solutions would be greatly appreciated. Please help.
Dec 22 '06 #5

P: 6
I was able to run the executable by calling system(command) where command was "ssh -X servername /home/dir1/dir2/executable &". Thanks for michaelb and sashi for attempting to help me.
Dec 22 '06 #6

P: 1
Hi
I am trying to execute a system command in my "C" code running on a Ubuntu Linux machine. The code is supposed to open a secure shell connection to another machine, change directories to a given directory and run an executable on that machine. I have configured the remote machine through ssh keygen to be able to authenticate my account and bypass the password. here is my "C" code:


void create_server(char *servermcnm)
{
char command1[100] = "ssh -X ";
strcat(command1,servermcnm);
strcat(command1," &");
char command2[100] = "cd ~/P1/P1*";
system(command1);
system(command2);
system("./server &");
}

In the above code, servermcnm is the name of the remote machine. The system(command1) call works, because I am able to reach a terminal session on the other machine, but I want the system(command2) line and system("./server &) to execute on the remote machine, but it doesn't work.
------------------------------------------
Hi Pvadi,
I am trying to do the same as you are asking here. Meaning execute remote shell , I have been looking and successfully generate the public / private key using ssh-gen , but I do not know how to bypass the password , so it will not prompt me the password.
You had mentioned here that you know how to set up to make it bypass prompting the password. Would you shed some lights for me ?
Thanks a lot,
Austin1
Mar 1 '07 #7

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