Hello, on Wednesday 09 May 2012 at 11:26, Lluís Batlle i Rossell wrote: > On Tue, May 08, 2012 at 10:06:15PM -0400, Martin Gagnon wrote: > > On Wed, May 09, 2012 at 12:09:36AM +0200, Lluís Batlle i Rossell wrote: > > > On Tue, May 08, 2012 at 05:55:38PM -0400, Leo Razoumov wrote: > > > > 9. Runs user's shell or command. > > > But I don't know why the sshd man page does not say that though. :) > > > > This is for bash... But for ksh (default on OpenBSD and QNX for > > instance) any echo on .kshrc or on .profile will *not* appear when > > doing: "ssh host command" neither with "ssh -T host command". > > > > There's a chance that sshd manpage expect ksh behavior since openssh is > > developped by OpenBSD crowd and their system use ksh by default.. > > Ah very interesting. > And can you run: ssh host "cat < ~/.kshrc" > ? > > If so, it would mean the command is run by ksh, and not by sshd.
Why resort to dubious experimentation when code source is available?
Truth lies in the source code. I gather the relevant code is at the end
of do_child() from session.c
/*
* If we have no command, execute the shell. In this case, the shell
* name to be passed in argv[0] is preceded by '-' to indicate that
* this is a login shell.
*/
if (!command) {
[...]
execve(shell, argv, env);
[...]
perror(shell);
exit(1);
}
/*
* Execute the command using the user's shell. This uses the -c
* option to execute the command.
*/
argv[0] = (char *) shell0;
argv[1] = "-c";
argv[2] = (char *) command;
argv[3] = NULL;
execve(shell, argv, env);
perrror(shell);
exit(1);
}
Greping across the source for `exec[a-z ]*(` provides with few enough
results to check them all; but the code flow for `ssh host command` is
quite simple, jumping from client code to server code through a
grep '"exec"'.
So I admit I was wrong, as far as I can tell `ssh host command` does
spawn a shell. I guess I was misled by my own dubious experimentation:
`ssh host pstree` showed pstree as a direct child of sshd, but it seems
my shell (zsh) uses exec() to run pstree, while sh and tcsh don't (and
so appear between sshd and pstree).
However I have no idea about the behavior of bash or ksh with regard to
banners or startup scripts.
Hoping this helps,
Natacha
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