Environment variables are unavailable when running scripts over ssh

Question

Suppose I have two hosts: A and B with users a and b. B is Windows machine with Cygwin installed, if this matters.

B is configured to be accessed from A through SSH without password (it contains A's public RCA key), so I can run commands on it from A in the following way:

ssh b@B [command]

But when I try to run a command, that requires to access an environment variable, the command fails:

[15:54:08] - a@A - ~
$ ssh b@B 'echo $ANT_HOME'

returns empty string.

The same command, if connected directly (not through SSH) is executed correctly:

b@B ~
$ echo $ANT_HOME
/cygdrive/c/PROGRA~1/apache-ant-1.9.0

The latter is possible because the relevant variables were exported in "bash_profile":

export JAVA_HOME="/cygdrive/c/PROGRA~1/Java/jdk1.7.0_45"
export ANT_HOME="/cygdrive/c/PROGRA~1/apache-ant-1.9.0"

but for some reason this is not applied to the SSH case.

---

Some additional info that may be useful.

Host B has Windows XP + Cygwin. CYGWIN sshd is run under SYSTEM account. JAVA_HOME and ANT_HOME are defined in "system" environment variables part in Windows.

When I run "$ ssh b@B env" command, it does not print ANT_HOME or JAVA_HOME, but if I include them in sshd_config file, it does. But even then simple command ssh b@B 'echo $ANT_HOME' does not work as I would expect.

Please give me a hint what needs to be done to run the command through SSH.

Answer 1

From the man pages of my server:

1. Reads the file ~/.ssh/environment, if it exists, and users are allowed to change their environment. See the PermitUserEnvironment option in sshd_config(5).

You need to declare the environment variables and allow them in the remote server location /etc/ssh/sshd_config, by enabling the property PermitUserEnvironment as PermitUserEnvironment yes and set your environment variables in ~/.ssh/environment.

Answer 2

When you run a command as an argument to ssh, the command is run directly by sshd; the shell is not involved.

You can verify this using something like the following:

ssh b@B pstree

It is the shell (bash in this case) that pulls in your .bash_profile, and it only does so if the shell is invoked as a login shell, or if the shell was invoked with the --login option (see the bash man page; look for INVOCATION). The environment you get when running a command directly is set by things like sshd and PAM when you log in.

Thus, if you want your .bash_profile, you need to run it under the shell and you need to run the shell as an interactive or login shell, like this:

ssh b@B "bash -l -c 'env'"

That should get you output you desire. The only thing to watch out for is that quoting gets tricky pretty quickly. Note that on Linux, at least,

ssh b@B bash -l -c 'env'

will not get you a login shell (I'm not sure why).

Answer 3

If you do not want to mess with the SSH configuration and just start a program then create a script locally that defines the variables and runs the program. Now scp the script and run it over ssh.

 > cat <<EOF >run.sh
X=42 program
EOF
 > scp user@host run.sh user@host:path/to/target/ || exit
 > ssh user@host "cd path/to/target/; bash run.sh"

Now program is started under the environment variables X=42 on the other machine. Under Linux this works perfectly, however, for Cygwin the path to bash might be missing. But the point is that you can tunnel environment variables this way.