Ssh – Why does bash invocation differ on AIX when using telnet vs ssh

aixbashsshtelnet

I am using an AIX 5.3 server with a .bashrc file set up to echo "Executing bashrc." When I log in to the server using ssh and run:

bash -c ls

I get:

Executing bashrc
.
..
etc....

However, when I log in with telnet as the same user and run the same command I get:

.
..
etc....

Clearly in the telnet case, the .bashrc was not invoked. As near as I can tell this is the correct behaviour given that the shell is non-interactive in both cases (it is invoked with -c). However, the ssh case seems to be invoking the shell as interactive. It does not appear to be invoking the .profile, so it is not creating a login shell. I cannot see anything obviously different between the environments in the two cases.

What could be causing the difference in bash behaviour?

Best Answer

Check to make sure that the login shell you're in doesn't have an alias or a different PATH depending on whether you're logged in via ssh or telnet. Compare this each way:

type -a bash

There could be some conditional code in one of:

/etc/profile
/.bash_profile
~/.bash_login
~/.profile
~/.bashrc

That sets the PATH differently or creates an alias depending on whether you're logged in via ssh or telnet. The PATH could point to different versions of Bash that are compiled with different options. An alias could be something like alias bash='bash -i'.

If you echo $SHELL as Nikolaidis suggests, that's only going to show what's set in /etc/passwd as your login shell. It might be more reliable to use ps. If for some reason you're getting a shell other than Bash, you'll need to check its startup files and environment to see if the PATH or aliases are different. Generally, though, your interactive shell shouldn't affect how explicitly calling bash -c works.

And you're correct about this:

As near as I can tell this is the correct behaviour given that the shell is non-interactive in both cases (it is invoked with -c).

Related Solutions

Linux – the difference between a ‘Login’ and an ‘Interactive’ bash shell

In your login shell's profile files you can set up some things that you will use during your session, and which only need to be done once. Some ideas:

create a temporary file containing the IP address you connected from, later on you can include it in some scripts setting firewall rules.
run ssh-agent, ask for your SSH keys, and store the SSH agent environment variables in a file.
if that is a limited machine, and your co-workers want to be aware of each others logins, write(1) messages informing them of your login.

In a non-login shell's files (.bashrc) you should configure your shell:

Fancy prompt
set aliases
set history options
define custom shell functions
export environment variables, (maybe PAGER, EDITOR if system-wide settings suck)
load ssh-agent variables saved in .bash_profile

Usually, you would include .bashrc from .bash_profile with the following. Then login shell gets all your customizations, and .bash_profile file does not have to duplicate things that are already in .bashrc.

[[ -f ~/.bashrc ]] && . ~/.bashrc

Bash – Both bashrc and bash_profile won’t seemingly source? VirtualMin Clean install

There are a whole lot of questions here that you have, and not much information provided for us to go on. But, here are some attempts:

The first thing I'd check is to see if your PATH is getting set at all when logging in. To check that, login to the terminal and type echo $PATH. If the things you added are there, then great, on to the next problem. If they aren't there, then I'd verify you are actually running bash with echo $SHELL. If you are, can you check if ANYTHING in ~/.bashrc or ~/.bash_profile is getting set? I'd find something innocuous and change it, then logout and back in to see if it took effect (or just add something like FOO="bar";export FOO, then test it after login with echo $FOO). If your .bashrc and .bash_profile aren't getting run, I'd check to see if .profile is getting run, and then also check if /etc/profile and /etc/rc/bash.bashrc are there and are calling the user's profiles correctly.

If you find that things are actually getting into .bash_profile, then I'd check to make sure your script and the directory it is placed in has the appropriate permissions, is executable, and that the directory is actually in your path (maybe something else is setting the path variable after you set it and overwriting your changes?).

If none of that works, then please post the following here and maybe we'll be able to see something more:

env
echo $SHELL
echo $PATH
cat ~/.bashrc
cat ~/.profile
cat ~/bash_profile
cat /etc/profile
cat /etc/bash.bashrc

Best Answer

Related Solutions

Linux – the difference between a ‘Login’ and an ‘Interactive’ bash shell

Bash – Both bashrc and bash_profile won’t seemingly source? VirtualMin Clean install

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