Notes

Remote Environment Variables for SSH Commands

Daniel Weibel
Created 16 Jul 2013

With SSH it is possible to execute “one-shot” commands on a remote host, in the following way:

ssh user@host some_command

This causes the SSH client to log in to the remote machine, execute the specified command, and log out again.

The problem is that when the SSH client logs in to the remote machine, it does not source the ~/.bash_profile and ~/.bashrc files of the remote machine. This means that any environment variables defined in these files, including customisations to the PATH variable, are not available to the command executed by the SSH client.

This might prevent the client from executing certain commands, if, for example, the PATH doesn’t contain the directory of the command, and the client doesn’t know where the command executable is saved on the server.

Which Environment Variables are Available to the Client?

With the following command you can see the evironment variables that are available to the command executed by the SSH client:

ssh user@host env

For the PATH variable, the value is most likely something like

PATH=/usr/bin:/bin:/usr/sbin:/sbin

which is the default value of PATH on UNIX systems.

Make Custom Variables Available to the Client

Perform the following actions on the remote machine:

  1. In the following file: 
     /etc/sshd_config

    change the line

     #PermitUserEnvironment no

    to

     PermitUserEnvironment yes
  2. Create the following file: 
     ~/.ssh/environment

    And add to this file variable definitions required by the client, for example:

     PATH=$PATH:/usr/local/bin

Now, all the variable defined in the ~/.ssh/environment file should be available to the SSH client when it logs in to the remote machine.

You can test this by executing the following command on the client machine again:

ssh user@host env

References