How to know openssh-server is already installed?

Question

I use an installation script and here's two of my installation commands:

function InstallChrome()
{
    if ( which google-chrome 1>/dev/null ); then
        echo "Chrome is installed"
        return
    fi

    echo "Installing Google Chrome ..."

    wget https://dl.google.com/linux/direct/google-chrome-stable_current_amd64.deb -O chrome
    sudo dpkg -i chrome

    echo "Installed Google Chrome"
}

So basically I search for the program installed by apt and if it exists, I won't run the apt commands.

The reason is that it's way faster than letting the apt check.

However, this code does not work:

function InstallSshServer()
{
    if ( which openssh-server 1>/dev/null ); then
        echo "SSH Server is installed"
        return;
    fi

    echo "Installing SSH Server ..."

    sudo apt install openssh-server -y

    echo "Installed SSH Server"
}

What is the name of the program openssh-server installs on my machine? How can I check if it's already installed or not?

Why do you need to test whether it's already installed or not? The `apt-install` command would not fail if it was installed. — Kusalananda, Nov 15 '22 at 17:13
@Kusalananda, as I mentioned, it's faster. For an installation script that installs like 20 programs on a machine, the difference is clearly visibile. — Saeed Neamati, Nov 16 '22 at 05:14
Even if you call `apt install` once with all the packages in the same invocation? You would not need to call `apt install` 20 times. — Kusalananda, Nov 16 '22 at 09:21

Stephen Kitt · Answer 1 · 2022-11-15T14:39:09.007

openssh-server installs /usr/sbin/sshd, you should look for that. Packages don’t necessarily install a binary by the same name, and the binaries they install aren’t necessarily on all users’ paths. Thus, explicitly:

[ -x /usr/bin/sshd ] || sudo apt install -y openssh-server

dpkg -L will tell you what files are installed by a given package, if that package is installed. Binaries can be listed with

dpkg -L openssh-server | grep bin/

apt-file list will show you files installed by a package without installing it first.

As an aside, Why not use "which"? What to use then? would make useful reading for your script.

score 1 · Answer 2 · answered Nov 15 '22 at 14:25

1

What I would do using bash:

if ! type -p sshd &>/dev/null; then
    sudo apt-get install -y openssh-server
fi

answered Nov 15 '22 at 14:25

Gilles Quénot

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That will only work if `/usr/sbin` is on the user’s `PATH`. – Stephen Kitt Nov 15 '22 at 14:35

ramius · Answer 3 · 2022-11-15T14:54:02.590

Here is an adaptation of a little script I made for a similar case:

#!/bin/bash

prompt_confirm() {
    while true; do
            read -r -n 1 -p "${1:-} [y/n]: " REPLY
            case ${REPLY} in
                    [yY]) echo ; return 0 ;;
                    [nN]) echo ; return 1 ;;
                    *) printf " \033[31m %s \n\033[0m" "Incorrect input, please type y (yes) ou n (no)."
            esac
    done
}

# Check if openssh-server is installed
if ! command -v sshd &> /dev/null
then
    echo -e "\nThe openssh-server is not installed."
    if prompt_confirm "Would you like to install it now?";
    then
            apt install -y openssh-server
    else
            echo -e "\nOk, quitting.\n"
            exit
    fi
fi

Of course, you can use only the check part, the prompt y/n isn't required.

command -v is the recommended way to test if command is available on a system.

How to know openssh-server is already installed?

3 Answers3