Bash function doesn't work for remote ssh command execution although interactive shell function fine

Question

I define a function in .bash_aliases file and include it in my .bashrc file.

My .bash_aliases file:

function dmidecode() {
        if [[ $1 == -t && $2 == 1 ]]; then
                cat ~/some_file
        else
                command dmidecode "$@"
        fi
}

The function is: when someone executes the command: dmidecode -t 1, bash reads the content from ~/some_file and return.

My .bashrc file:

# ~/.bashrc: executed by bash(1) for non-login shells.
# see /usr/share/doc/bash/examples/startup-files (in the package bash-doc)
# for examples

# If not running interactively, don't do anything
case $- in
    *i*) ;;
      *) return;;
esac

# don't put duplicate lines or lines starting with space in the history.
# See bash(1) for more options
HISTCONTROL=ignoreboth

# append to the history file, don't overwrite it
shopt -s histappend

# for setting history length see HISTSIZE and HISTFILESIZE in bash(1)
HISTSIZE=1000
HISTFILESIZE=2000

# check the window size after each command and, if necessary,
# update the values of LINES and COLUMNS.
shopt -s checkwinsize

# If set, the pattern "**" used in a pathname expansion context will
# match all files and zero or more directories and subdirectories.
#shopt -s globstar

# make less more friendly for non-text input files, see lesspipe(1)
[ -x /usr/bin/lesspipe ] && eval "$(SHELL=/bin/sh lesspipe)"

# set variable identifying the chroot you work in (used in the prompt below)
if [ -z "${debian_chroot:-}" ] && [ -r /etc/debian_chroot ]; then
    debian_chroot=$(cat /etc/debian_chroot)
fi

# set a fancy prompt (non-color, unless we know we "want" color)
case "$TERM" in
    xterm-color|*-256color) color_prompt=yes;;
esac

# uncomment for a colored prompt, if the terminal has the capability; turned
# off by default to not distract the user: the focus in a terminal window
# should be on the output of commands, not on the prompt
#force_color_prompt=yes

if [ -n "$force_color_prompt" ]; then
    if [ -x /usr/bin/tput ] && tput setaf 1 >&/dev/null; then
        # We have color support; assume it's compliant with Ecma-48
        # (ISO/IEC-6429). (Lack of such support is extremely rare, and such
        # a case would tend to support setf rather than setaf.)
        color_prompt=yes
    else
        color_prompt=
    fi
fi

if [ "$color_prompt" = yes ]; then
    PS1='${debian_chroot:+($debian_chroot)}\[\033[01;32m\]\u@\h\[\033[00m\]:\[\033[01;34m\]\w\[\033[00m\]\$ '
else
    PS1='${debian_chroot:+($debian_chroot)}\u@\h:\w\$ '
fi
unset color_prompt force_color_prompt

# If this is an xterm set the title to user@host:dir
case "$TERM" in
xterm*|rxvt*)
    PS1="\[\e]0;${debian_chroot:+($debian_chroot)}\u@\h: \w\a\]$PS1"
    ;;
*)
    ;;
esac

# enable color support of ls and also add handy aliases
if [ -x /usr/bin/dircolors ]; then
    test -r ~/.dircolors && eval "$(dircolors -b ~/.dircolors)" || eval "$(dircolors -b)"
    alias ls='ls --color=auto'
    #alias dir='dir --color=auto'
    #alias vdir='vdir --color=auto'

    alias grep='grep --color=auto'
    alias fgrep='fgrep --color=auto'
    alias egrep='egrep --color=auto'
fi

# colored GCC warnings and errors
#export GCC_COLORS='error=01;31:warning=01;35:note=01;36:caret=01;32:locus=01:quote=01'

# some more ls aliases
alias ll='ls -alF'
alias la='ls -A'
alias l='ls -CF'

# Add an "alert" alias for long running commands.  Use like so:
#   sleep 10; alert
alias alert='notify-send --urgency=low -i "$([ $? = 0 ] && echo terminal || echo error)" "$(history|tail -n1|sed -e '\''s/^\s*[0-9]\+\s*//;s/[;&|]\s*alert$//'\'')"'

# Alias definitions.
# You may want to put all your additions into a separate file like
# ~/.bash_aliases, instead of adding them here directly.
# See /usr/share/doc/bash-doc/examples in the bash-doc package.

if [ -f ~/.bash_aliases ]; then
    . ~/.bash_aliases
fi

# enable programmable completion features (you don't need to enable
# this, if it's already enabled in /etc/bash.bashrc and /etc/profile
# sources /etc/bash.bashrc).
if ! shopt -oq posix; then
  if [ -f /usr/share/bash-completion/bash_completion ]; then
    . /usr/share/bash-completion/bash_completion
  elif [ -f /etc/bash_completion ]; then
    . /etc/bash_completion
  fi
fi

It works when I interactively execute the command by typing the command in the bash shell. However, it doesn't work when I tried to execute it remotely. It said dmidecode command not found (I didn't install dmidecode tool but I write a function to point it to somewhere.). The remote connection is good because I can remotely execute commands like "ls" or "pwd". It just doesn't work for the functions that I wrote.

And I tried to put shopt -s expand_aliases in the .bashrc file. It doesn't solve the problem also.

FYI, here is my test code for remote command execution:

from paramiko import client

class ssh:
    client = None

    def __init__(self, address, username, password, port=22):
        print("Connecting to server.")
        self.client = client.SSHClient()
        self.client.set_missing_host_key_policy(client.AutoAddPolicy())
        self.client.connect(address, port, username=username, password=password, look_for_keys=False)

    def sendCommand(self, command):
        if(self.client):
            stdin, stdout, stderr = self.client.exec_command(command)
            while not stdout.channel.exit_status_ready():
                # Print data when available
                if stdout.channel.recv_ready():
                    alldata = stdout.channel.recv(1024)
                    prevdata = b"1"
                    while prevdata:
                        prevdata = stdout.channel.recv(1024)
                        alldata += prevdata

                    print(str(alldata, "utf8"))
        else:
            print("Connection not opened.")

def main():
    connection = ssh("my_ip", "username", "password", 22)
    connection.sendCommand("dmidecode -t 1") # this doesn't work, "dmidecode command not found"
    connection.sendCommand("pwd") # this works


if __name__ == "__main__":
    main()

Any idea on this?

Answer 1

Your title says it all, actually. When you do ssh login@remote 'my command', your shell is NOT interactive, by definition, since you provide a command. However, ~/.bashrc is only sourced by bash when you shell is interactive.

When you execute ssh login@remote 'my command', here is what happens:

• your machine connects first to "remote" with user "login"
• then sshd, the ssh server running on "remote", executes your shell with the parameters -c 'my command' (i.e. bash -c 'my command' since you are using bash)
• since it is called with -c, bash executes directly your command without reading your startup files

The solution? Source your startup file before executing your command:

ssh login@remote 'source ~/.bash_aliases; my command'